JP3781220B2 - Image signal encoding method, image signal encoding apparatus, and image signal transmission method - Google Patents

Description

による平均値演算を行い、図２（Ｂ）で示す第２階層の１画素（例えばＹ₁₁）を生成する。なお、画素Ｙ₁₃、Ｙ₃₁、……も第１階層の４画素平均により、同様に生成される。
【００１８】
同様に、平均化回路１４６は、図２（Ｂ）に示すような第２階層のブロツク内の４画素（例えばＹ₁₁、Ｙ₁₃、Ｙ₃₁、Ｙ₃₃）を用いて、次式、
【数２】

による平均値演算を行い、図２（Ｃ）で示す第３階層の１画素（例えばＺ₁₁）を生成する。なお、画素Ｚ₁₅、Ｚ₅₁、……も第２階層の４画素平均により、同様に生成される。
【００１９】
間引き回路１４２、１４５は、ブロツク化回路１４１からのブロツク化データＤ１３２及びブロツク化回路１４４からのブロツク化データＤ１３４をそれぞれ受信し、４画素で構成されるブロツク化データＤ１３２、Ｄ１３４のうち１画素を取り除き、各ブロツクにつき取り除かれた１画素を除く残り３画素で構成される間引きデータＤ１３６、Ｄ１３７を形成し、この間引きデータＤ１３６、Ｄ１３７を量子化回路１４７、１４８にそれぞれ送出する。すなわち、間引き回路１４２は、図２（Ｃ）の点線で示すような画素Ｘ₁₁、Ｘ₁₃、……を間引きにより削除し、間引き回路１４５は、図２（Ｂ）の点線で示すような画素Ｙ₁₁、Ｙ₁₅、……を間引きにより削除する。
【００２０】
従つて、第１階層の量子化回路１４７及び第２階層の量子化回路１４８の量子化対象となる画素は、図２（Ｃ）及び図２（Ｂ）の実線で示される画素Ｘ₁₂、Ｘ₂₁、Ｘ₂₂、……やＹ₁₃、Ｙ₃₁、Ｙ₃₃……であり、第１階層について見れば、第１階層の全ての画素を量子化して伝送する場合と比較して、伝送画素数を3/4 に低減できる。また、第２階層について見れば、平均演算により生成された第２階層の全ての画素を量子化して伝送する場合と比較して、伝送画素数を3/4 に低減する。
【００２１】
また、全体的に見れば、画像信号符号化装置１４０においては、第１階層画像データＤ１３１のみを圧縮して伝送する場合と比較して、等しい伝送画素数で、複数階層の画像データを伝送することができるようになされている。この結果、画像信号符号化装置１４０は、伝送情報量を増加させずに、複数階層の画像データを伝送することができる。なお、間引き回路１４２、１４５において間引かれた画素は、後述する復号側（受信側）で簡単な算術式を用いて復元することができる。
【００２２】
量子化回路１４７、１４８及び１４９は、それぞれ間引きデータＤ１３６、Ｄ１３７及び第３階層画像データＤ１３５の各画素（８ビツト）を、例えば２ビツトで再量子化して情報量を圧縮する。また、第３階層の量子化回路１４９は、量子化時の誤差の極性を表わす量子化誤差情報信号Ｓ１を量子化制御回路２００に送出する。
【００２３】
量子化制御回路２００は、量子化誤差情報信号Ｓ１に基づいて第２階層及び第１階層の量子化回路１４８及び１４７に量子化制御信号Ｓ２及びＳ３を送出し、量子化回路１４８及び１４７の量子化誤差の極性が量子化回路１４９の誤差の極性と同じになるように量子化特性を制御する。なお、この場合、量子化回路１４８及び１４７では、量子化回路１４９によつて量子化されている最上位階層画素に空間的に対応する下位階層画素が量子化されているものとする。
【００２４】
このことを図３を用いて具体的に説明する。図３は、入力されるデータが１画素当り８ビツトのデータであり、かつ０〜２５５までのレベルをとり得る場合に、０〜６３のレベルの画素には量子化値「０」を出力し、６４〜１２７のレベルの画素には量子化値「１」を出力し、１２８〜１９１のレベルの画素には量子化値「２」を出力し、１９２〜２５５のレベルの画素には量子化値「３」を出力するような２ビツト量子化を表現したものである。これは、歪み最小規範と呼ばれ、量子化誤差を最小とするために従来一般的に用いられている手法である。
【００２５】
第１実施例の画像信号符号化装置１４０では、量子化回路１４７及び１４８において、このような歪み最小規範を用いずに、最上位階層である量子化回路１４９の量子化誤差の極性に応じた量子化を行うようになされている。例えば、量子化回路１４９に入力された画素データが、図３に示されるようなＬ１のようなレベルにあつた場合、量子化回路１４９は歪み最小規範に従つて量子化値「３」を出力する。このとき、量子化回路１４９は、量子化誤差が＋δ1 、すなわち正極性であることを示す量子化誤差情報信号Ｓ１を量子化制御回路２００に送出する。
【００２６】
このとき、量子化回路１４７及び１４８は、歪み最小規範に従わずに、量子化制御信号Ｓ２及びＳ３に基づいて量子化誤差が正極性となるような量子化処理を行う。つまり、例えば、量子化回路１４７又は１４８に入力された画素データが図３に示されるようなＬ２のようなレベルにあつた場合、歪み最小規範に従えば量子化値「２」を出力するに対して、この第１実施例の量子化回路１４７、１４８は、量子化制御回路２００からの量子化誤差情報信号Ｓ１（この場合、Ｓ１は正極性を表している）に基づいて、量子化値「３」を出力するようになされている。また、例えば、入力された画素データがＬ３のようなレベルにあつた場合は、量子化制御回路２００からの量子化誤差情報信号Ｓ１に基づいて、量子化値「２」を出力するようになされている。これは、歪み最小規範に従つた場合と同様となる。
【００２７】
量子化回路１４７、１４８、１４９によつて得られた再量子化データＤ１３８、Ｄ１３９、Ｄ１４０は、それぞれ可変長符号化回路（ＶＬＣ）１５０、１５１、１５２に供給される。可変長符号化回路１５０〜１５２のそれぞれは、再量子化データＤ１３８〜Ｄ１４０に対して発生度数の大きい量子化コードほど短いハフマンコードを割り当て、各再量子化データＤ１３８〜Ｄ１４０を可能な限り少ない符号量で表現した第１階層符号化データＤ１４１、第２階層符号化データＤ１４２及び第３階層符号化データＤ１４３をそれぞれ形成し、この第１階層符号化データＤ１４１、第２階層符号化Ｄ１４２及び第３階層符号化Ｄ１４３を伝送フオーマツト変換回路１５３に送出する。
【００２８】
伝送フオーマツト変換回路１５３は、第１階層符号化データＤ１４１、第２階層符号化データＤ１４２及び第３階層符号化データＤ１４３を所定の順序で配列したり、各階層符号化データの階層を識別するための識別コードを付加することにより、伝送画像データＤ１４４を形成して、この伝送画像データＤ１４４を出力する。この出力された伝送画像データＤ１４４は、その後、通信路１５４を介して受信側に供給されるか、もしくは記録伝送路を介してデイスク、テープ又は半導体メモリなどの記録媒体１５５に記録される。
【００２９】
このようにして形成された伝送画像データＤ１４４を復号する画像信号復号化装置１６０は、例えば、図４に示すように構成することができる。この画像信号復号化装置１６０は、通信路１５４を介して供給されるか、もしくは再生伝送路を介して記録媒体１５５から再生される伝送画像データＤ１４４をデータ分流回路１６１に入力する。データ分流回路１６１は、図示しないスイツチング回路を有し、伝送画像データＤ１４４に含まれる各階層の識別コードを参照して伝送画像データＤ１４４を第１階層符号化データＤ１５０、第２階層符号化データＤ１５１及び第３階層符号化データＤ１５２に分流し、これら第１階層符号化データＤ１５０、第２階層符号化データＤ１５１及び第３階層符号化データＤ１５２をそれぞれ可変長復号化回路（ＩＶＬＣ）１６２、１６３、１６４に送出する。
【００３０】
可変長復号化回路１６２、１６３、１６４は、それぞれ上述した図１に示された可変長符号化回路１５０、１５１、１５２と逆の処理を行し、ハフマン符号によつて表現されている第１階層符号化データＤ１５０、第２階層符号化データＤ１５１及び第３階層符号化データＤ１５２を再量子化コードで表現された再量子化データＤ１５３、Ｄ１５４、Ｄ１５５にそれぞれ変換する。そして、これらの再量子化データＤ１５３、Ｄ１５４、Ｄ１５５をそれぞれ逆量子化回路１６５、１６６、１６７に送出する。
【００３１】
逆量子化回路１６５は、上述した図１に示された量子化回路１４７によつて１画素当り２ビツトとされた再量子化データＤ１５３を例えば８ビツトのデータに逆量子化し、第１階層間引き復号データＤ１５６を生成する。そして、この第１階層間引き復号データＤ１５６を合成回路１６８及び画素生成回路１６９に送出する。逆量子化回路１６６は、上述した図１に示された量子化回路１４８によつて１画素当り２ビツトとされた再量子化データＤ１５４を例えば８ビツトのデータに逆量子化し、第２階層間引き復号データＤ１５７を生成する。そして、この第２階層間引き復号データＤ１５７を合成回路１７０及び画素生成回路１７１に送出する。
【００３２】
逆量子化回路１６７は、上述した図１に示された量子化回路１４９によつて１画素当り２ビツトとされた再量子化データＤ１５５を例えば８ビツトのデータに逆量子化し、これを第３階層復号画像データＤ１５８として出力する。そして、この第３階層復号画像データＤ１５８を例えば出力端子を介して表示画素数の少ない低解像度のテレビジヨンモニタに送出すると共に画素生成回路１７１に送出する。
【００３３】
画素生成回路１７１は、第３階層復号画像データＤ１５８と第２階層間引き復号データＤ１５７を用いて、上述した図１に示された画像信号符号化装置１４０の間引き回路１４５で間引かれた第２階層画素（すなわち図２（Ｂ）の点線で示す画素）を復元する。例えば間引きにより削除された第２階層の画素Ｙ₁₁は、次式、
【数３】

のような演算を行うことにより復元する。同様に、平均化によつて生成した上位階層画素と、上位階層画素の生成のために用いられ、かつ間引かれなかつた画素とを用いて全ての間引かれた画素を復元する。
【００３４】
合成回路１７０は、このようにして生成された第２階層の復元画素データＤ１５９を第２階層間引き復号データＤ１５７中の所定の位置に挿入して合成することにより、第２階層復号画像データＤ１６０を形成する。そして、この第２階層復号画像データＤ１６０を例えば出力端子を介して表示画素数が中程度のテレビジヨンモニタに送出すると共に画素生成回路１６９に送出する。
【００３５】
画素生成回路１６９は、第２階層復号画像データＤ１６０と第１階層間引き復号データＤ１５６を用いて、上述した図１に示された画像信号符号化装置１４０の間引き回路１４２で間引かれた第１階層画素（すなわち図２（Ｃ）の点線で示す画素）を復元する。例えば間引きにより削除された第１階層画素Ｘ₁₁は、次式、
【数４】

のような演算を行うことにより復元する。同様に、平均化によつて生成した上位階層画素と、上位階層画素の生成のために用いられ、かつ間引かれなかつた画素とを用いて全ての間引かれた画素を復元する。
【００３６】
合成回路１６８は、このようにして生成された第１階層の復元画素データＤ１６１を第１階層間引き復号データＤ１５６中の所定の位置に挿入して合成することにより、第１階層復号画像データＤ１６２を形成する。そして、この第１階層復号画像データＤ１６２を出力端子を介して例えば表示画素数が多いハイビジヨンテレビモニタに送出する。
【００３７】
以上の構成において画像信号符号化装置１４０は、下位階層の複数画素の平均値によつて上位階層画素を生成することにより、複数階層の画像データＤ１３１、Ｄ１３３、Ｄ１３５を生成する。
【００３８】
これに加えて、画像信号符号化装置１４０は、最上位階層すなわち第３階層を除いた階層画像データについて、同じ平均演算に用いた画素のうちの１画素は復号側で簡単な算術演算によつて復元できるので伝送画素から除外する。この結果、画像信号符号化装置１４０においては、階層構造に起因する伝送画素数の増加を伴わない階層符号化処理を実現することができる。
【００３９】
ところで、画像信号符号化装置１４０では、再量子化回路１４７〜１４９によつて各階層画像データを再量子化することで各階層におけるデータ量を圧縮する。この結果、各再量子化データＤ１３８、Ｄ１３９、Ｄ１４０は、必然的に再量子化時の量子化誤差を含む値となる。そして、この量子化誤差が大きくなるほど復号画像データＤ１５８、Ｄ１６０、Ｄ１６２は、真値と比較して誤差が大きくなり、画質が劣化することになる。
【００４０】
そこで、画像信号符号化装置１４０及び画像信号復号化装置１６０における各階層での量子化誤差の影響について考える。ここで、各画素Ｚ₁₁、Ｙ₁₁、……の復号値をＺ₁₁′、Ｙ₁₁′、……とし、真値をＺ₁₁、Ｙ₁₁、……とし、量子化誤差をＥ（Ｚ₁₁）、Ｅ（Ｙ₁₁）……とすると、例えば逆量子化回路１６７によつて得られる第３階層の画素Ｚ₁₁の復号値Ｚ₁₁′は、次式、
【数５】

となる。また、逆量子化回路１６６によつて得られる第２階層の画素Ｙ₁₃、Ｙ₃₁、Ｙ₃₃の復号値Ｙ₁₃′、Ｙ₃₁′、Ｙ₃₃′は、次式、
【数６】

となる。
【００４１】
ところが、画素生成回路１７１によつて復元される第２階層画素Ｙ₁₁は、（３）式に基づいて生成されるので、その復号値Ｙ₁₁′は、次式、
【数７】

となり、Ｚ₁₁についての量子化誤差が４倍となつて影響する。
【００４２】
また、逆量子化回路１６５によつて得られる第１階層画素Ｘ₁₂、Ｘ₂₁、Ｘ₂₂、Ｘ₁₄、Ｘ₂₃、Ｘ₂₄の復号値Ｘ₁₂′、Ｘ₂₁′、Ｘ₂₂′、Ｘ₁₄′、Ｘ₂₃′、Ｘ₂₄′は、次式、
【数８】

となるが、画素生成回路１６９によつて復元される第１階層画素Ｘ₁₃、Ｘ₃₁、Ｘ₃₃は、（４）式に基づいて生成されるので、その復号値Ｘ₁₃′、Ｘ₃₁′、Ｘ₃₃′は、次式、
【数９】

となり、それぞれの復号値Ｘ₁₃′、Ｘ₃₁′、Ｘ₃₃′に、空間的に対応する第２階層画素Ｙ₁₃、Ｙ₃₁、Ｙ₃₃、すなわち対応する上位階層画素についての量子化誤差が４倍となつて影響する。
【００４３】
さらに、画素生成回路１７１を経て画素生成回路１６９によつて復元される第１階層画素Ｘ₁₁においては、その復号値Ｘ₁₁′は、次式、
【数１０】

で示すように、復号値Ｘ₁₁′に、第２階層画素Ｙ₁₃、Ｙ₃₁、Ｙ₃₃についての量子化誤差が４倍となつて影響するのに加えて、第３階層画素Ｚ₁₁についての量子化誤差が１６倍となつて影響する。
【００４４】
図５は、この各復号画素値Ｚ₁₁′、Ｙ₁₁′、Ｙ₁₃′、……に対する各量子化誤差Ｅ（Ｚ₁₁）、Ｅ（Ｙ₁₃）、Ｅ（Ｙ₃₁）、……の影響の大きさの様子を示している。図５を見れば明らかなように、上位階層での量子化誤差は下位階層での復号値に大きな影響を及ぼす。
【００４５】
これを考慮して、本発明の第１実施例においては、最上位階層の画素Ｚ₁₁を量子化したときの量子化誤差の極性に基づいて、この最上位階層画素Ｚ₁₁に空間的に対応する下位階層画素Ｙ₁₃、Ｙ₃₁、Ｙ₃₃、Ｘ₁₂、Ｘ₂₁、Ｘ₂₂の量子化を、その量子化誤差の極性が最上位階層の画素Ｚ₁₁を量子化したときの量子化誤差の極性と同じになるように制御する。つまり、例えば、（７）式から明らかなように、平均演算の逆処理により第２階層画素Ｙ₁₁を復号した際に、上位階層画素であるＺ₁₁の量子化誤差Ｅ（Ｚ₁₁）及び同階層（第２階層）画素（同一ブロツク内に存在する画素）であるＹ₁₃、Ｙ₃₁、Ｙ₃₃の量子化誤差Ｅ（Ｙ₁₃）、Ｅ（Ｙ₃₁）、Ｅ（Ｙ₃₃）が含まれることになる。しかしながら、上位階層画素であるＺ₁₁の量子化誤差Ｅ（Ｚ₁₁）と同階層画素であるＹ₁₃、Ｙ₃₁、Ｙ₃₃の量子化誤差Ｅ（Ｙ₁₃）、Ｅ（Ｙ₃₁）、Ｅ（Ｙ₃₃）との関係は、（７）式から明らかなように、相殺する関係にある。
【００４６】
よつて、上位階層画素であるＺ₁₁の量子化誤差Ｅ（Ｚ₁₁）と同階層画素であるＹ₁₃、Ｙ₃₁、Ｙ₃₃の量子化誤差Ｅ（Ｙ₁₃）、Ｅ（Ｙ₃₁）、Ｅ（Ｙ₃₃）が共に同一の極性を持つように符号化すれば、復号時に量子化誤差を低減することができる。したがつて、本発明の第１実施例によれば、（７）式から明らかなように、符号化時に最上位階層と同一の極性となるように、下位階層を量子化することにより、復号時に量子化誤差が互いに相殺されることになり、下位階層での画質劣化を低減することができる。
【００４７】
また、同様に、（１０）式から明らかなように、平均演算の逆処理により第１階層画素Ｘ₁₁を復号した際に、最上位階層（第３階層）画素であるＺ₁₁の量子化誤差Ｅ（Ｚ₁₁）及び上位階層（第２階層）であるＹ₁₃、Ｙ₃₁、Ｙ₃₃の量子化誤差Ｅ（Ｙ₁₃）、Ｅ（Ｙ₁₃）、Ｅ（Ｙ₃₃）及び同階層（第１階層）画素（同一ブロツク内に存在する画素）であるＸ₁₂、Ｘ₂₁、Ｘ₂₂の量子化誤差Ｅ（Ｘ₁₂）、Ｅ（Ｘ₂₁）、Ｅ（Ｘ₂₂）が含まれることになる。しかしながら、最上位階層画素であるＺ₁₁の量子化誤差Ｅ（Ｚ₁₁）と、上位階層であるＹ₁₃、Ｙ₃₁、Ｙ₃₃の量子化誤差Ｅ（Ｙ₁₃）、Ｅ（Ｙ₁₃）、Ｅ（Ｙ₃₃）及び同階層画素であるＸ₁₂、Ｘ₂₁、Ｘ₂₂の量子化誤差Ｅ（Ｘ₁₂）、Ｅ（Ｘ₂₁）、Ｅ（Ｘ₂₂）との関係は、（１０）式から明らかなように、相殺する関係にある。
【００４８】
よつて、最上位階層画素であるＺ₁₁の量子化誤差Ｅ（Ｚ₁₁）と、上位階層であるＹ₁₃、Ｙ₃₁、Ｙ₃₃の量子化誤差Ｅ（Ｙ₁₃）、Ｅ（Ｙ₁₃）、Ｅ（Ｙ₃₃）及び同階層画素であるＸ₁₂、Ｘ₂₁、Ｘ₂₂の量子化誤差Ｅ（Ｘ₁₂）、Ｅ（Ｘ₂₁）、Ｅ（Ｘ₂₂）が共に同一の極性を持つように符号化すれば、復号時に量子化誤差を低減することができる。したがつて、本発明の第１実施例によれば、（１０）式から明らかなように、符号化時に最上位階層と同一の極性となるように、下位階層を量子化することにより、復号時に量子化誤差が互いに相殺されることになり、下位階層での画質劣化を低減することができる。
【００４９】
このように、画像信号符号化装置１４０においては、復号側で上位階層から下位階層へと伝播する量子化誤差を考慮した量子化処理を行うことができ、量子化誤差に基づく画質劣化を低減することができるようになされている。
【００５０】
以上の第１実施例の構成によれば、上位階層の１画素を生成するために同じ平均値演算に用いた複数の下位階層画素のうちの１画素分の画素データＹ₁₁、Ｙ₁₅、……、Ｘ₁₁、Ｘ₁₃、……を伝送しないようにすると共に、最上位階層画素を量子化したときの量子化誤差の極性に応じて、当該最上位階層画素に対応する下位階層画素を量子化する際の量子化特性を、量子化誤差が最上位階層画素を量子化したときの量子化誤差の極性と同じになるように制御するようにしたことにより、圧縮効率を向上し得ると共に画質劣化を低減し得る。
【００５１】
（２）第２実施例
図６は、全体として第２実施例の画像信号符号化装置１８０を示している。第１の実施例と比較して、最上位階層を除いて階層間データの残差（差分）圧縮符号化する点を除いて、図１の画像信号符号化装置１４０と同一の構成を有する。したがつて、図１と対応する部分については同一符号を付す。
【００５２】
すなわち、第１実施例の画像信号符号化装置１４０が各画素をＰＣＭ（Pulse Code Modulation ）の形式で伝送するようになされているのに対して、この第２実施例の画像信号符号化装置１８０は、各画素をＤＰＣＭ（Differential Pulse Code Modulation ）の形式で伝送するようになされている。したがつて、画像信号符号化装置１８０は、一段と伝送情報量を低減させることができる。
【００５３】
具体的に説明すると、画像信号符号化装置１８０は、第３階層画像データＤ１３５及び第２階層ブロツク化データＤ１３４を差分回路１８１に供給する。そして、差分回路１８１によつて第３階層画像データＤ１３５と第２階層ブロツク化データＤ１３４との間で空間的に対応する画素同士の差分を演算して第２階層差分データＤ１７０を形成し、この第２階層差分データＤ１７０を間引き回路１８２に送出する。このとき、差分回路１８１は、第２階層画素Ｙ₁₃、Ｙ₃₁、Ｙ₃₃の差分値ΔＹ₁₃、ΔＹ₃₁、ΔＹ₃₃を、これらの画素に対応する上位階層画素Ｚ₁₁を用いて、次式、
【数１１】

のようにして求める。
【００５４】
画像信号符号化装置１８０は、同様にして、第２階層ブロツク化データＤ１３４及び第１階層ブロツク化データＤ１３２を差分回路１８３に供給する。差分回路１８３によつて第２階層ブロツク化データＤ１３４と第１階層ブロツク化データＤ１３２との間で空間的に対応する画素同士の差分を演算して第１階層差分データＤ１７１を形成し、この第１階層差分データＤ１７１を間引き回路１８４に送出する。このとき、差分回路１８３は、第１階層画素Ｘ₁₂、Ｘ₂₁、Ｘ₂₂の差分値ΔＸ₁₂、ΔＸ₂₁、ΔＸ₂₂を、これらの画素に対応する上位階層画素Ｙ₁₁を用いて、次式、
【数１２】

のようにして求める。
【００５５】
間引き回路１８４、１８２は、上述した図１に示される間引き回路１４２、１４５と同様に、ブロツク化回路１４１からのブロツク化データＤ１３２及びブロツク化回路１４４からのブロツク化データＤ１３４をそれぞれ受信する。そして、４画素で構成されるブロツク化データＤ１３２、Ｄ１３４に対応して各ブロツクにつき４画素で構成されている第１階層及び第２階層差分データＤ１７１、Ｄ１７０の中からそれぞれ１画素を間引き、各ブロツクにつき取り除かれた１画素を除く残り３画素によつて構成される階層差分間引きデータＤ１７２、Ｄ１７３を形成し、この階層差分間引きデータＤ１７２、Ｄ１７３を量子化回路１８５、１８６に送出する。
【００５６】
第３階層の量子化回路１８７は、平均化回路１４６からの第３階層画像データを受信し、第１実施例と同様に、各画素を歪み最小規範に従つて、例えば２ビツトに量子化する。そして、量子化回路１８７は、量子化誤差が正極性であるか負極性であるかどうかを示す量子化誤差情報信号Ｓ１１を量子化制御回路２１０に送出する。
【００５７】
ここで、第１階層の量子化回路１８５及び第２階層の量子化回路１８６は、第１実施例と同様に、第３階層（最上位階層）の量子化回路１８７の量子化誤差の極性に応じて量子化制御回路２１０から出力される量子化制御信号Ｓ１２及びＳ１３に基づいて、量子化特性が制御される。すなわち、上位階層画素の量子化回路１８７による量子化誤差の極性が正極性であつた場合には、この上位階層画素に空間的に対応する下位階層画素を量子化するときの量子化回路１８５及び１８６の量子化特性が、量子化誤差の極性が正極性となるように制御される。また、上位階層画素の量子化回路１８７による量子化誤差の極性が負極性であつた場合には、この上位階層画素に空間的に対応する下位階層画素を量子化するときの量子化回路１８５及び１８６の量子化特性が、量子化誤差の極性が負極性となるように制御される。
【００５８】
量子化回路１８５、１８６、１８７により得られた再量子化データＤ１７４、Ｄ１７５、Ｄ１７６は、可変長符号化回路（ＶＬＣ）１５０、１５１、１５２によつて可変長符号化され、 第１階層、第２階層及び第３階層符号化データＤ１７７、Ｄ１７８、Ｄ１７９として出力される。そして、これらの第１階層、第２階層及び第３階層符号化データＤ１７７、Ｄ１７８、Ｄ１７９が続く伝送フオーマツト変換回路１５３に入力され、伝送フオーマツト変換回路１５３は、伝送画像データＤ１８０を形成して、それを出力する。この出力された伝送画像データＤ１８０は、その後、通信路１８８を介して受信側に供給されるか、もしくは記録伝送路を介してデイスク、テープや半導体メモリなどの記録媒体１８９に記録される。
【００５９】
このようにして形成された伝送画像データＤ１４４を復号する画像信号復号化装置１９０は、例えば、図７に示すように構成することができる。画像信号復号化装置１９０において、図４に示された画像信号復号化装置１６０との対応部分に同一符号を付している。画像信号復号化装置１９０は、通信路１８８を介して供給されるか、もしくは再生伝送路を介して記録媒体１８９から再生される伝送画像データＤ１８０をデータ分流回路１６１に入力する。データ分流回路１６１は、伝送画像データＤ１８０を第１階層、第２階層及び第３階層符号化データＤ１８１、Ｄ１８２及びＤ１８３に分流し、これらの第１階層、第２階層及び第３階層符号化データＤ１８１、Ｄ１８２及びＤ１８３は、可変長復号化回路（ＩＶＬＣ）１６２、１６３及び１６４にそれぞれ供給される。
【００６０】
可変長復号化回路（ＩＶＬＣ）１６２、１６２及び１６４のそれぞれは、第１階層、第２階層及び第３階層符号化データＤ１８１、Ｄ１８２及びＤ１８３をそれぞれ可変長復号し、再量子化データＤ１８４、Ｄ１８５、Ｄ１８６を形成し、これらの再量子化データＤ１８４、Ｄ１８５、Ｄ１８６を逆量子化回路１９１、１９２及び１９３にそれぞれ送出する。なお、可変長復号化回路（ＩＶＬＣ）１６２、１６３及び１６４は、図６で示された可変長符号化回路（ＶＬＣ）１５０、１５１及び１５２にそれぞれ対応する逆処理を実行する。
【００６１】
逆量子化回路１９１、１９２及び１９３は、１画素当り２ビツトに再量子化されてなる再量子化データＤ１８４、Ｄ１８５及びＤ１８６を１画素当り８ビツトでなるデータにそれぞれ逆量子化し、第１階層及び第２階層の階層差分間引きデータＤ１８７及びＤ１８８並びに第３階層復号画像データＤ１８９をそれぞれ生成する。なお、逆量子化回路１９１、１９２及び１９３は、図６で示された量子化回路１８５、１８６及び１８７にそれぞれ対応する逆処理を実行する。
【００６２】
第３階層復号画像データＤ１８９は、そのまま低解像度のテレビジヨンモニタ等に出力されると共に、加算回路１９４及び画素生成回路１９５に送出される。加算回路１９４は、次式、
【数１３】

のような加算演算を行い、第２階層間引き復号データＤ１９０を算出する。
【００６３】
画素生成回路１９５は、第２階層差分間引きデータＤ１８８と第３階層復号画像データＤ１８９とを用いて、図６で示された間引き回路１８２で間引かれた第２階層画素Ｙ₁₁を、次式、
【数１４】

により求める。この（１４）式は、上述した（３）式と比較すると、第３階層画素Ｚ₁₁の乗算係数が（３）式では「４」であつたのに対して、この式では「１」となつていることが分かる。このことは（１４）式において、第２階層の画素値に対する第３階層の画素値の影響が（３）式と比べて小さいことを意味する。
【００６４】
合成回路１９６は、第２階層間引き復号データＤ１９０と第２階層復元画素データＤ１９１とを合成して第２階層復号画像データＤ１９２を形成し、この第２階層復号画像データＤ１９２を出力端子を介してテレビジヨンモニタ等に出力すると共に、加算回路１９７及び画素生成回路１９８に送出する。加算回路１９７は、次式、
【数１５】

のような加算演算を行い、第１階層間引き復号データＤ１９３を算出する。
【００６５】
画素生成回路１９８は、第１階層差分間引きデータＤ１８７と第２階層復号画像データＤ１９２とを用いて、図６に示された間引き回路１８４で間引かれた第１階層画素Ｘ_１３、Ｘ_３１、Ｘ_３３を、次式、
【数１６】

により求める。また、画素生成回路１９８は、間引かれた第１階層画素Ｘ_１１を、次式、
【数１７】

により求める。
【００６６】
合成回路１９９は、第１階層間引き復号データＤ１９３と第１階層復元画素データＤ１９４とを合成して、第１階層復号画像データＤ１９５を形成する。そして、この第１階層復号画像データＤ１９５を出力端子を介して、例えば高解像度のテレビジヨンモニタ等に出力する。
【００６７】
次に、第１実施例と同様に、この第２実施例の画像信号符号化装置１８０及び画像信号復号化装置１９０における各階層での量子化誤差の影響について考える。
逆量子化回路１９３によつて得られる第３階層の画素Ｚ₁₁の復号値Ｚ₁₁′は、（５）式と同じとなる。また加算回路１９４によつて得られる第２階層の画素Ｙ₁₃、Ｙ₃₁、Ｙ₃₃の復号値Ｙ₁₃′、Ｙ₃₁′、Ｙ₃₃′は、次式、
【数１８】

で示す値となる。
【００６８】
また、画素生成回路１９５によつて復元される第２階層画素Ｙ_１１は、（１４）式に基づいて生成されるので、その復号値Ｙ_１１′は、次式、
【数１９】

で示す値となる。このように、第２実施例の画像信号符号化装置１８０は、最上位階層データを除いて、各階層間の差分データを伝送データとして伝送しており、（１９）式を上述した（７）式と比較すると、第３階層画素Ｚ_１１の量子化誤差Ｅ（Ｚ_１１）の乗算係数が（７）式では「４」であつたのに対して、「１」となつていることが分かる。
【００６９】
このことは、この第２実施例の符号化復号化によれば、第３階層画素の量子化誤差が第２階層画素の復号に与える影響を１／４程度に低減させることができることを意味する。つまり、第１の実施例では、（１９）式から明らかなように、階層間の差分を演算しているために、第３階層の画素Ｚ_１１の量子化誤差は、第２階層の復号画素値Ｙ_１１′、Ｙ_１３′、Ｙ_３１′、Ｙ_３３′のすべてに反映されることになる。したがつて、第３階層画素の量子化誤差が第２階層画素の復号に与える影響を低減させることができる。
【００７０】
また加算回路１９７によつて得られる第１階層画素Ｘ_１２、Ｘ_２１、Ｘ_２２、Ｘ_３２、Ｘ_４１、Ｘ_４２の復号値Ｘ_１２′、Ｘ_２１′、Ｘ_２２′、Ｘ_３２′、Ｘ_４１′、Ｘ_４２′は、次式、
【数２０】

で示される値となり、画素生成回路１９８によつて復元される第１階層画素Ｘ_３１の復号値Ｘ_３１′は、次式、
【数２１】

で示される値となる。
【００７１】
さらに画素生成回路１９５を経て画素生成回路１９８によつて復元される第１階層画素Ｘ_１１の復号値Ｘ_１１′は、次式、
【数２２】

で示される値となり、Ｚ_１１についての量子化誤差が等倍となつて影響し、Ｙ_１３、Ｙ_３１、Ｙ_３３についての量子化誤差も等倍となつて影響する。しかしながらこの（２２）式と（１０）式を比較すれば明らかなように、Ｚ_１１、Ｙ_１３、Ｙ_３１、Ｙ_３３の量子化誤差が復号値Ｘ_１１′に与える影響は第１実施例の場合よりも格段に低減されている。つまり、第１の実施例では、例えば、（１０）式から明らかなように、第３階層の画素Ｚ_１１の量子化誤差及び第２階層の画素Ｙ_１３、Ｙ_３１、Ｙ_３３の量子化誤差は、第１階層の復号画素値Ｘ_１１′のみに反映されており、第１階層の復号画素Ｘ_１２′、Ｘ_２１′、Ｘ_２２′には反映されていない。
【００７２】
しかしながら、第２の実施例では、（２２）式から明らかなように、階層間の差分を演算しているために、第３階層の画素Ｚ₁₁の量子化誤差及び第２階層の画素Ｙ₁₃、Ｙ₃₁、Ｙ₃₃の量子化誤差は、第１階層の復号画素Ｘ₁₁′、Ｘ₁₂′、Ｘ₂₁′に反映されることになる。したがつて、第３階層画素の量子化誤差及び第２階層画素の量子化誤差が第１階層画素の復号に与える影響を低減させることができる。
【００７３】
したがつて、以上の第２実施例の画像信号符号化装置の構成によれば、入力画像データＤ１３１から平均値演算により得された複数の階層画像データの各階層データと隣接上位階層データとの階層差分データを生成し、最上位階層データＤ１３５と複数の階層差分データＤ１７２、Ｄ１７３をそれぞれ量子化して複数の階層符号化データを生成する画像信号符号化装置１８０において、最上位階層を除く各階層の画素のうち隣接下位階層の画素及び自分の階層の画素を用いた算術演算によつて復元できる差分画素データΔＹ₁₁、ΔＹ₁₅、……、ΔＸ₁₁、ΔＸ₁₃、……を伝送しないようにすると共に、最上位階層画素を量子化したときの量子化誤差の極性に応じて、その最上位階層画素に対応する下位階層画素を量子化する際の量子化特性を、量子化誤差が最上位階層画素を量子化したときの量子化誤差の極性と同じになるように制御するようにしたことにより、画質劣化を抑制した状態で圧縮効率を一段と向上し得る。
【００７４】
（３）第３実施例
図８は、全体として第３実施例の画像信号符号化装置４００を示している。この画像信号符号化装置４００は、第２実施例と比較して、適応予測回路４０１及び４０２を設けたことを除いて第２実施例の画像信号符号化装置１８０と同様の構成を有する。したがつて、図６と対応部分に同一符号を付して示している。
【００７５】
適応予測回路４０１は、第３階層画像データＤ１３５に基づいて所定の予測処理を行い、第２階層画像データＤ１３４に対応する第２階層予測データＤ４００を生成する。そして、この第２階層予測データを差分回路１８１に送出する。同様に、適応予測回路４０２は、第２階層画像データＤ１３４に基づいて所定の予測処理を行い、第１階層画像データＤ１３２に対応する第１階層予測データＤ４０１を生成する。そして、この第１階層予測データを差分回路１８３に送出する。
【００７６】
実際上、適応予測回路４０１及び４０２は、クラス分類適応処理を適用して、複数の上位階層画素から下位階層の１画素を予測する。具体的には、予測しようとする下位階層の画素をその空間的に近傍の複数の上位階層画素のレベル分布に基づいてクラス分類する。また、適応予測回路４０１及び４０２は、予め学習によつて獲得された、クラス毎に複数の予測係数あるいは１個の予測値を格納したメモリ（図示せず）を有し、上記クラス分類で決定されたクラスに対応した複数の予測係数あるいは１個の予測値をメモリから読み出す。予測値の場合は、その予測値がそのまま予測画素として使用され、予測係数の場合は、複数の予測係数と複数の画素との線形一次結合により予測値を生成する。
【００７７】
また、予測値は正規化されている場合は、この予測値に所定の処理を施して予測画素を生成する。このようなクラス分類適応処理の詳細は、例えば特願平4-155719号に開示されている。また、このようなクラス分類適応処理のアルゴリズムは、すでに知られている。また、第３の実施例の適応予測回路において、クラス分類適応処理のアルゴリズムが使用されているが、本発明はこれに限らず、現在使用されている他の予測方法を使用してもよい。
【００７８】
画像信号符号化装置４００により圧縮符号化された伝送画像データＤ１８０′を復号する画像信号復号化装置１９０′の構成を図９に示す。この画像信号復号化装置１９０′は、第２実施例の画像信号復号化装置１９０と比較して、適応予測回路４０１′及び４０２′を設けたことを除いて第２実施例の画像信号復号化装置１９０と同様の構成を有する。したがつて図７との対応部分に同一符号を付して示している。
【００７９】
この第３実施例による画像信号復号化装置１９０′において、第３階層復号データＤ１８９′を入力する第１の適応予測回路４０１′は、図８に示した適応予測回路４０１に対応するクラス分類適応処理を第３階層復号データＤ１８９′に基づいて実行し、この結果得られる第２階層予測データＤ４００′を画素生成回路１９５に送出する。画素生成回路１９５は、第２階層の逆量子化回路１９２から出力される第２階層差分間引きデータＤ１８８′と第２階層予測データＤ４００′とを用いて、図８で示された間引き回路１８２で間引かれた第２階層画素を生成する。また、第３階層復号データＤ１８９′に基づいて第１の適応予測回路４０１′によつて得られた第２階層予測データＤ４００′は、第２階層の逆量子化回路１９２から出力される第２階層差分間引きデータＤ１８８′に加算される。この加算により得られる第２階層間引き復号データＤ１９０′は、画素生成回路９５によつて生成された第２階層画素Ｄ１９１′と合成され、第２階層復号画像データＤ１９２′となる。
【００８０】
また、第２階層復号データＤ１９２′を入力する第２の適応予測回路４０２′は、図８に示した適用予測回路４０２に対応するクラス分類適応処理を第２階層復号データＤ１９２′に基づいて実行し、この結果得られる第１階層予測データＤ４０１′を画素生成回路１９８に送出する。画素生成回路１９８は、第１階層の逆量子化回路１９１から出力される第１階層差分間引きデータＤ１８７′と第１階層予測データＤ４０１′とを用いて、図８で示された間引き回路１８４で間引かれた第１階層画素を生成する。
【００８１】
また、第２階層復号データＤ１９２′に基づいて第２の適応予測回路４０２′によつて得られた第１階層予測データＤ４０１′は、第１階層の逆量子化回路１９１から出力される第１階層差分間引きデータＤ１８７′に加算される。この加算により得られる第１階層間引き復号データＤ１９３′は、画素生成回路１９８によつて生成された第１階層画素Ｄ１９４′と合成され、第１階層復号画像データＤ１９５′となる。
【００８２】
以上の第３実施例の構成によれば、最上位階層画素を量子化したときの量子化誤差の極性に応じて、当該最上位階層画素に対応する下位階層画素を量子化する際の量子化特性を、量子化誤差が最上位階層を量子化したときの量子化誤差の極性と同じになるように制御することにより、圧縮効率を向上し得ると共に画質劣化を低減し得る。また、適応予測回路４０１及び４０２を用いることによつて差分回路１８１及び１８３からそれぞれ得られる第２階層差分データＤ１７０′及び第１階層差分データＤ１７１′の残差を一段と少なくすることができるので、伝送情報量を一段と低減し得る画像信号符号化装置４００を実現できる。
【００８３】
（４）第４実施例
この第４実施例では、第１〜第３実施例において上述したように、最上位階層画素を量子化したときの量子化誤差の特性に応じて、その最上位階層画素に空間的に対応する下位階層画素を量子化する際の量子化特性を、量子化誤差が最上位階層画素を量子化したときの量子化誤差の極性と同じになるように制御することに加えて、上位階層の量子化回路ほど量子化ビツト数を大きく（量子化幅を小さくして）細かい量子化を行うようにする。このようにすれば、第１〜第３の実施例の効果に加えてさらに一段と復号時の画質劣化を低減し得るようになされている。
【００８４】
この第４実施例の場合、第１実施例について上述した画像信号符号化装置１４０において、量子化回路１４７で１ビツトの量子化を行い、量子化回路１４８で４ビツトの量子化を行い、量子化回路１４９で１６ビツトの量子化を行うように各量子化回路１４７〜１４９の量子化特性を制御する。この場合の量子化ビツト数は、下位階層データを復元する際の復元画素値に与える上位階層における量子化誤差の影響の程度を考慮して量子化ビツト数を選定する。
【００８５】
この結果、例えば上述した（１０）式について考えると、量子化誤差Ｅ（Ｚ₁₁）の誤差の程度は、量子化誤差Ｅ（Ｘ₁₂）、Ｅ（Ｘ₂₁）、Ｅ（Ｘ₂₂）と比べて１／１６倍となり、また量子化誤差Ｅ（Ｙ₁₃）、Ｅ（Ｙ₃₁）、Ｅ（Ｙ₃₃）の程度は量子化誤差Ｅ（Ｘ₁₂）、Ｅ（Ｘ₂₁）、Ｅ（Ｘ₂₂）と比べて１／４倍となることにより、復号時に間引かれた画素を求めるために量子化誤差Ｅ（Ｚ₁₁）の誤差を１６倍したり、量子化誤差Ｅ（Ｙ₁₃）、Ｅ（Ｙ₃₁）、Ｅ（Ｙ₃₃）を４倍しても、これから得られる誤差は逆量子化回路１６５から直接得られる量子化誤差Ｅ（Ｘ₁₂）、Ｅ（Ｘ₂₁）、Ｅ（Ｘ₂₂）と同程度となる。従つて、上位階層での量子化歪みに基づく下位階層画像の画質劣化を格段に低減し得る。
【００８６】
また、上位階層データの量子化誤差の下位階層データに対する影響度は、最下位階層からの階層の段数及び上位階層データを生成するときに使用する画素数に関係してくる。したがつて、上位階層の量子化ビツト数を決定する際に、最下位階層からの階層の段数及び上位階層データを生成するときに使用する画素数に応じて、最下位階層に影響する量子化誤差を最小限にするような量子化ビツト数もしくはそれ以上の量子化ビツト数に設定すれば、画質劣化を低減した画像符号化装置を提供することができる。なお、このように上位階層の量子化ビツト数を多くするとその分伝送情報量も増えるように見えるが、上位階層ほど伝送画素数が少ないので量子化ビツト数を多くすることによる情報量の増加は実際上問題とならない程度に抑えられている。
【００８７】
また、第２及び第３実施例について上述した画像信号符号化装置１８０及び４００において、量子化回路１８５で１ビツトの量子化を行い、量子化回路１８６で２ビツトの量子化を行い、量子化回路１８７で４ビツトの量子化を行うように各量子化回路１８５〜１８７の量子化特性を制御する。
【００８８】
このように第１実施例の各量子化回路について割り当てた量子化ビツト数に対して、第２及び第３実施例の各量子化回路について割り当てた量子化ビツト数を少なくしたのは、第２及び第３実施例においては、最上位階層データを除いて階層間の差分データを伝送している。したがつて、上述した（３）式と（１４）式、（７）式と（１９）式、（１０）式と（２２）式を比較すれば明らかなように、間引かれた画素を復元する際に量子化誤差にかかる乗算係数が第１実施例の場合よりも第２及び第３実施例の方が小さく抑えられているためである。つまり、量子化ビツト数は、下位階層に与える量子化誤差の影響度によつて決定される。
【００８９】
（５）他の実施例
なお、上述の実施例においては、３階層分の階層画像データＤ１３１、Ｄ１３４、Ｄ１３５を生成し、これを圧縮符号化して伝送する場合について述べたが、本発明はこれに限らず、順次平均値演算を繰り返すことにより４階層や５階層分の階層画像データを生成し、これを量子化によつて圧縮符号化して伝送する場合にも適用し得る。
【００９０】
また、上述の実施例においては、下位階層の４画素を用いた平均値演算によつて上位階層の１画素を生成する場合について述べたが、本発明はこれに限らず、例えば下位階層の６画素もしくはそれ以上の画素を用いた平均値演算によつて上位階層の１画素を生成するようにして階層画像データを生成するようにしても良い。
【００９１】
また上述の第４実施例においては、量子化回路４７、４８、４９の量子化ビツト数をそれぞれ１ビツト、４ビツト、１６ビツトとし、量子化回路８５、８６、８７の量子化ビツトをそれぞれ１ビツト、２ビツト、４ビツトとする場合について述べたが、本発明はこれに限らず、要は上位階層の量子化回路ほど細かい量子化幅に制御するようにすれば良い。
【００９２】
また、上述した実施例においては、量子化器をすべて線形量子化器として記載したが、本発明はこれに限らず、非線型量子化や適応量子化、さらには、ダイナミツクレンジに応じた適用量子化などを適用してもよい。
さらに、本発明の実施例は、ブロツク図を用いて示したハードウエアによつて実現しているが、本発明はこれに限らず、ＣＰＵやメモリなどを用いてソフトウエアで実現することも可能である。
【００９３】
なお、本発明の主旨を逸脱しない範囲において、さまざまな変形や応用例が考え得る。従つて、本発明の要旨は、実施例に限定されるものではない。
【００９４】
【発明の効果】
上述のように本発明によれば、平均値演算により生成した複数の階層画像データについて、上位階層の１画素を生成するために同じ平均値演算に用いた複数の下位階層画素のうちの１画素分の画素データを伝送対象から除外すると共に、最上位階層の画素データを量子化したときの量子化誤差が正値又は負値のいずれであるかを表す極性に応じて、当該最上位階層画素に空間的に対応する下位階層の画素データを量子化する際の量子化誤差の極性を、最上位階層画素データを量子化したときの量子化誤差の極性と同じになるように制御したことにより、圧縮効率が向上しかつ画質劣化が低減した階層符号化を実現することができる。
【図面の簡単な説明】
【図１】第１実施例による画像信号符号化装置の構成を示すブロツク図である。
【図２】階層化及び伝送画素の説明に供する略線図である。
【図３】量子化特性の制御の説明に供する略線図である。
【図４】第１実施例による画像信号復号化装置の構成を示すブロツク図である。
【図５】各階層における量子化誤差が各階層の復元画素に与える影響を表わす図表である。
【図６】第２実施例による画像信号符号化装置の構成を示すブロツク図である。
【図７】第２実施例による画像信号復号化装置の構成を示すブロツク図である。
【図８】第３実施例による画像信号符号化装置の構成を示すブロツク図である。
【図９】第３実施例による画像信号復号化装置の構成を示すブロツク図である。
【図１０】従来の階層符号化を実現する画像信号符号化装置の構成を示すブロツク図である。
【図１１】従来の階層符号化データを復号する画像信号復号化装置の構成を示すブロツク図である。
【符号の説明】
１４０、１８０、４００……画像信号符号化装置、１４３、１４６……平均化回路、１４２、１４５、１８２、１８４……間引き回路、１４７〜１４９、１８５〜１８７……量子化回路、１６０、１９０……画像信号復号化装置、４０１、４０２、４０１′、４０２′……適応予測回路、２００……量子化制御回路、Ｄ１３１……入力画像データ、Ｄ１３３……第２階層画像データ、Ｄ１３５……第３階層画像データ、Ｄ１４１、Ｄ１７７、Ｄ１７７′……第１階層符号化データ、Ｄ１４２、Ｄ１７８、Ｄ１７８′……第２階層符号化データ、Ｄ１４３、Ｄ１７９、Ｄ１７９′……第３階層符号化データ、Ｄ１４４、Ｄ１８０、Ｄ１８０′……伝送画像データ、Ｄ１５８、Ｄ１８９……第３階層復号画像データ、Ｄ１６０、Ｄ１９２……第２階層復号画像データ、Ｄ１６２、Ｄ１９５……第１階層復号画像データ、Ｄ１７０、Ｄ１７０′……第２階層差分データ、Ｄ１７１、Ｄ１７１′……第１階層差分データ、Ｄ４００……第２階層予測データ、Ｄ４０１……第１階層予測データ、Ｓ１……量子化誤差情報信号、Ｓ２、Ｓ３……量子化制御信号、Ｚ……第３階層画素、Ｙ……第２階層画素、Ｘ……第１階層画素。[0001]
【table of contents】
The present invention will be described in the following order.
TECHNICAL FIELD OF THE INVENTION
Conventional technology (FIGS. 10 and 11)
Problems to be solved by the invention
Means for solving the problem
BEST MODE FOR CARRYING OUT THE INVENTION
(1) 1st Example (FIGS. 1-5)
(2) Second embodiment (FIGS. 6 and 7)
(3) Third embodiment (FIGS. 8 and 9)
(4) Fourth embodiment
(5) Other embodiments
The invention's effect
[0002]
BACKGROUND OF THE INVENTION
The present invention records an image signal encoding method, an image signal encoding device, an image signal transmission method, and encoded data generated by an image signal encoding method or device that can be decoded by the image signal decoding device. In particular, predetermined image data is divided into multiple layers of image data having different resolutions, and the image data of each layer is encoded to generate encoded data (that is, the image data is hierarchically encoded). It is suitable to be applied to the case.
[0003]
[Prior art]
Conventionally, in this type of image signal encoding apparatus, high resolution input image data is used as first layer image data, second layer data having a resolution lower than that of the first layer data, and second layer data. Third layer data having a resolution lower than that of data is sequentially formed, and the plurality of layer data is compressed and encoded. Thereby, hierarchically encoded data for a plurality of hierarchies in which the amount of information is sequentially reduced is formed, and the plurality of hierarchically encoded data can be transmitted via a communication path or a recording / reproducing path.
[0004]
The image signal decoding apparatus that decodes the plurality of hierarchically encoded data can also decode all of the plurality of hierarchically encoded data, and any one of the hierarchical codes depending on the resolution of the television monitor corresponding to each It is also possible to select and decode a desired one of the digitized data. Thus, if only desired layer data is decoded from a plurality of layered layer data, desired image data can be obtained with a minimum necessary amount of transmission data.
[0005]
Here, as shown in FIG. 10, as this hierarchical encoding, for example, the image signal encoding device 1 that realizes encoding of four layers includes thinning filters 2, 3, and 4 and an interpolation filter 5, respectively. The reduced image data D2, D3, and D4 having low resolution are sequentially formed for the input image data D1 by the thinning filters 2, 3, and 4 for the input image data D1, and the interpolation filters 5, 6, and 7 are formed. Thus, the reduced image data D2, D3, and D4 are returned to the resolution data D5, D6, and D7 before reduction, respectively.
[0006]
Outputs D2 to D4 of the thinning filters 2 to 4 and outputs D5 to D7 of the interpolation filters 5 to 7 are input to the difference circuits 8, 9, and 10, respectively, and difference data D8, D9, and D10 are generated by the difference circuits. Is done. Since the frequency distribution of the difference data D8 to D10 is concentrated in the vicinity of 0, the image encoding device 1 can reduce the data amount of the hierarchical data and reduce the signal power. In addition, the amount of data can be further reduced by using run-length encoding, Huffman encoding, or the like in a variable-length encoding circuit arranged in the subsequent stage. Here, each of the difference data D8 to D10 and the reduced image data D4 has a size of 1, 1/4, 1/16, 1/64 with respect to the input image data D1.
[0007]
The difference data D8 to D10 obtained from the respective difference circuits 8 to 10 and the reduced image data D4 obtained from the thinning filter are encoded by the encoders 11, 12, 13, and 14, respectively, and subjected to compression processing. The As a result, the first, second, third and fourth hierarchical data D11, D12, D13 and D14 having different resolutions are sent from the encoders 11, 12, 13, and 14 to the communication path in a predetermined order. It is recorded on the recording medium via the transmission path.
[0008]
The first to fourth hierarchical data D11 to D14 transmitted in this way are decoded by the image signal decoding apparatus 20 shown in FIG. That is, the first to fourth hierarchical data D11 to D14 supplied from the communication path or the recording medium via the input terminals are respectively decoded by the decoders 21, 22, 23, and 24. As a result, The decoded fourth layer data D24 is output from the decoder 24.
[0009]
The output of the decoder 23 is added to the interpolation data of the fourth hierarchical data D24 obtained from the interpolation filter 26 in the adding circuit 29, whereby the third hierarchical data D23 is restored. Similarly, the output of the decoder 22 is added to the interpolation data of the third hierarchy data D23 obtained from the interpolation filter 27 in the adder circuit 30, whereby the second hierarchy data D22 is restored. Further, the output of the decoder 21 is added to the interpolation data of the second hierarchical data D22 obtained from the interpolation filter 28 in the adding circuit 31, whereby the first hierarchical data D21 is restored.
[0010]
[Problems to be solved by the invention]
However, in the image signal encoding apparatus 1 that realizes such hierarchical encoding, the input image data D1 is divided into a plurality of hierarchical data, and each hierarchical data is encoded. The amount increases. Therefore, there is a problem that the compression efficiency is reduced as compared with a high efficiency coding method that does not use hierarchical coding.
[0011]
Further, in the image signal decoding apparatus 20, the hierarchical data D24 and D23 are sequentially moved from the upper hierarchical data to the lower hierarchical data so that the lower hierarchical data is restored based on the hierarchical data restored in the upper hierarchy. , D22, D21 are restored. Accordingly, when the encoded upper layer data D14 and D13 are decoded and an error due to compression encoding is included in the decoded data, the lower layer restored layer data D21 or the lower layer where high resolution is originally desired. A compression coding error is propagated to D22, and there is a problem that image quality deterioration based on the error appears very conspicuously in the decompression layer data of the lower layer.
[0012]
The present invention has been made in consideration of the above points. An image signal encoding method and an image signal encoding apparatus that can improve compression efficiency and reduce image quality degradation when hierarchically encoding image data. An image signal transmission method and a recording medium on which encoded data encoded by an image signal encoding method or apparatus decodable by an image signal decoding apparatus is recorded are proposed.
[0013]
[Means for Solving the Problems]
In order to solve such a problem, in the present invention, after each layer data is generated by an average value calculation, one pixel among a plurality of lower layer pixels used for the same average value calculation to generate one pixel of the upper layer Quantization error when the pixel data of the highest layer is quantized The polarity of whether the value is positive or negative Quantization when quantizing lower layer pixel data spatially corresponding to the highest layer pixel Error polarity Is controlled to be the same as the polarity of the quantization error when quantizing the highest layer pixel data, it is possible to realize hierarchical encoding with improved compression efficiency and reduced image quality degradation.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[0015]
(1) First embodiment
FIG. 1 shows an image signal encoding apparatus 140 according to the first embodiment as a whole. In the first embodiment, a case is shown in which layer data for three layers is formed, and the data for these three layers are respectively compressed and encoded. The image signal encoding device 140 divides the high-resolution input image data D131 (hereinafter referred to as first layer image data) into small blocks of 2 lines × 2 pixels in the block circuit 141 to obtain the first Hierarchical blocking data D132 is formed, and the first hierarchical blocking data D132 is sent to the thinning circuit 142 and the averaging circuit 143.
[0016]
The averaging circuit 143 averages the pixel values in each block of the block data D132 to obtain input image data D13. 1 The second layer image data D133 reduced to 1/4 is generated, and the second layer image data D133 is sent to the block circuit 144. Similar to the blocking circuit 141, the blocking circuit 144 divides the second layer image data D133 into small blocks of 2 lines × 2 pixels to form second layer blocking data D134. Blocking data D134 of the above hierarchy is sent to the thinning circuit 145 and the averaging circuit 146.
[0017]
Similar to the averaging circuit 143, the averaging circuit 146 averages the pixel values in each block of the blocked data D134 and reduces it to 1/4 of the second hierarchy image data D133, that is, the first hierarchy. Third layer image data D135 reduced to 1/16 of the image data D131 is generated. That is, as shown by the dotted line in FIG. 2C, the averaging circuit 143 has four pixels (eg, X ₁₁ , X ₁₂ , X _{twenty one} , X _{twenty two} )
[Expression 1]

Is used to calculate the average value, and one pixel in the second hierarchy shown in FIG. ₁₁ ) Is generated. Pixel Y ₁₃ , Y ₃₁ ,... Are also generated in the same manner by averaging four pixels in the first layer.
[0018]
Similarly, the averaging circuit 146 has four pixels (for example, Y) in the block of the second hierarchy as shown in FIG. ₁₁ , Y ₁₃ , Y ₃₁ , Y ₃₃ )
[Expression 2]

Is used to calculate the average value, and one pixel (for example, Z) in the third hierarchy shown in FIG. ₁₁ ) Is generated. Pixel Z ₁₅ , Z ₅₁ ,... Are also generated in the same manner by averaging the four pixels in the second layer.
[0019]
The decimation circuits 142 and 145 receive the block data D132 from the block circuit 141 and the block data D134 from the block circuit 144, respectively. One of the block data D132 and D134 composed of four pixels is received. Then, thinned data D136 and D137 composed of the remaining three pixels excluding the removed one pixel are formed for each block, and the thinned data D136 and D137 are sent to the quantization circuits 147 and 148, respectively. In other words, the thinning-out circuit 142 has a pixel X as shown by the dotted line in FIG. ₁₁ , X ₁₃ ,... Are deleted by thinning, and the thinning circuit 145 displays the pixel Y as shown by the dotted line in FIG. ₁₁ , Y ₁₅ , ... are deleted by thinning out.
[0020]
Accordingly, the pixel to be quantized by the first-level quantization circuit 147 and the second-level quantization circuit 148 is the pixel X indicated by the solid line in FIGS. 2C and 2B. ₁₂ , X _{twenty one} , X _{twenty two} ............ Y ₁₃ , Y ₃₁ , Y ₃₃ In the first layer, the number of transmission pixels can be reduced to 3/4 compared to the case where all the pixels in the first layer are quantized and transmitted. Further, regarding the second layer, the number of transmission pixels is reduced to 3/4 compared to the case where all the pixels of the second layer generated by the average calculation are quantized and transmitted.
[0021]
Overall, the image signal encoding device 140 transmits image data of a plurality of layers with the same number of transmission pixels as compared with the case where only the first layer image data D131 is compressed and transmitted. It has been made so that it can. As a result, the image signal encoding device 140 can transmit multiple layers of image data without increasing the amount of transmission information. Note that the pixels thinned out by the thinning circuits 142 and 145 can be restored using a simple arithmetic expression on the decoding side (receiving side) described later.
[0022]
The quantization circuits 147, 148, and 149 requantize each pixel (8 bits) of the thinned data D136, D137, and the third layer image data D135, for example, by 2 bits, and compress the information amount. Further, the quantization circuit 149 in the third hierarchy sends a quantization error information signal S1 indicating the polarity of the error at the time of quantization to the quantization control circuit 200.
[0023]
The quantization control circuit 200 sends the quantization control signals S2 and S3 to the quantization circuits 148 and 147 of the second hierarchy and the first hierarchy based on the quantization error information signal S1, and the quantization of the quantization circuits 148 and 147 The quantization characteristic is controlled so that the polarity of the quantization error becomes the same as the polarity of the error of the quantization circuit 149. In this case, in the quantization circuits 148 and 147, it is assumed that the lower layer pixels spatially corresponding to the highest layer pixels quantized by the quantization circuit 149 are quantized.
[0024]
This will be specifically described with reference to FIG. FIG. 3 shows that when the input data is 8-bit data per pixel and can take a level from 0 to 255, a quantized value “0” is output to the pixels from 0 to 63. , The quantized value “1” is output to the pixels of 64 to 127, the quantized value “2” is output to the pixels of 128 to 191 level, and the quantized value is output to the pixels of level 192 to 255. This is a representation of 2-bit quantization that outputs the value “3”. This is called a distortion minimum criterion, and is a method generally used in the past to minimize the quantization error.
[0025]
In the image signal encoding device 140 of the first embodiment, the quantization circuits 147 and 148 do not use such a distortion minimum norm, and according to the quantization error polarity of the quantization circuit 149 which is the highest layer. Quantization is performed. For example, when the pixel data input to the quantization circuit 149 is at a level such as L1 as shown in FIG. 3, the quantization circuit 149 outputs a quantization value “3” according to the minimum distortion criterion. To do. At this time, the quantization circuit 149 sends a quantization error information signal S1 indicating that the quantization error is + δ1, that is, positive polarity, to the quantization control circuit 200.
[0026]
At this time, the quantization circuits 147 and 148 perform a quantization process such that the quantization error becomes positive based on the quantization control signals S2 and S3 without following the minimum distortion norm. That is, for example, when the pixel data input to the quantization circuit 147 or 148 is at a level such as L2 as shown in FIG. 3, the quantized value “2” is output according to the minimum distortion criterion. On the other hand, the quantization circuits 147 and 148 of the first embodiment are based on the quantization error information signal S1 from the quantization control circuit 200 (in this case, S1 represents positive polarity). “3” is output. For example, when the input pixel data is at a level such as L3, the quantization value “2” is output based on the quantization error information signal S1 from the quantization control circuit 200. ing. This is the same as when the minimum distortion criterion is followed.
[0027]
Re-quantized data D138, D139, and D140 obtained by the quantizing circuits 147, 148, and 149 are supplied to variable length coding circuits (VLC) 150, 151, and 152, respectively. Each of the variable length coding circuits 150 to 152 assigns a shorter Huffman code to the requantized data D138 to D140 as the generated code has a higher frequency, and assigns each requantized data D138 to D140 as few codes as possible. The first layer encoded data D141, the second layer encoded data D142, and the third layer encoded data D143 expressed in terms of quantities are formed, respectively, and the first layer encoded data D141, the second layer encoded D142, and the third layer encoded data are formed. The hierarchical encoding D143 is sent to the transmission format conversion circuit 153.
[0028]
The transmission format conversion circuit 153 arranges the first layer encoded data D141, the second layer encoded data D142, and the third layer encoded data D143 in a predetermined order, and identifies the layer of each layer encoded data. Is added to form transmission image data D144 and output this transmission image data D144. The output transmission image data D144 is then supplied to the receiving side via the communication path 154 or recorded on a recording medium 155 such as a disk, tape, or semiconductor memory via the recording transmission path.
[0029]
The image signal decoding device 160 that decodes the transmission image data D144 formed in this way can be configured as shown in FIG. 4, for example. The image signal decoding device 160 inputs transmission image data D144 supplied from the recording medium 155 via the communication path 154 or reproduced from the recording medium 155 to the data diversion circuit 161. The data diversion circuit 161 has a switching circuit (not shown), and refers to the identification code of each layer included in the transmission image data D144, the transmission image data D144 as the first layer encoded data D150, the second layer encoded data D151. And the third layer encoded data D152, and the first layer encoded data D150, the second layer encoded data D151 and the third layer encoded data D152 are respectively converted into variable length decoding circuits (IVLC) 162, 163, To 164.
[0030]
The variable-length decoding circuits 162, 163, and 164 perform processing reverse to that of the variable-length coding circuits 150, 151, and 152 shown in FIG. 1 described above, and are represented by Huffman codes. The layer encoded data D150, the second layer encoded data D151, and the third layer encoded data D152 are converted into requantized data D153, D154, and D155, respectively, expressed by a requantization code. These requantized data D153, D154, and D155 are sent to the inverse quantization circuits 165, 166, and 167, respectively.
[0031]
The inverse quantization circuit 165 dequantizes the requantized data D153, which has been converted to 2 bits per pixel by the quantization circuit 147 shown in FIG. Decoded data D156 is generated. Then, the first hierarchical decimation data D156 is sent to the synthesis circuit 168 and the pixel generation circuit 169. The inverse quantization circuit 166 dequantizes the requantized data D154, which has been converted to 2 bits per pixel by the quantization circuit 148 shown in FIG. Decoded data D157 is generated. Then, the second-layer thinned-out decoded data D157 is sent to the synthesis circuit 170 and the pixel generation circuit 171.
[0032]
The inverse quantization circuit 167 inversely quantizes the requantized data D155, which has been converted to 2 bits per pixel by the quantization circuit 149 shown in FIG. Output as hierarchical decoded image data D158. Then, the third-layer decoded image data D158 is sent to a low-resolution television monitor with a small number of display pixels via an output terminal, for example, and sent to the pixel generation circuit 171.
[0033]
The pixel generation circuit 171 uses the third-layer decoded image data D158 and the second-layer thinned-out decoded data D157, and the second thinned out by the thinning circuit 145 in the image signal encoding device 140 shown in FIG. 1 described above. A hierarchical pixel (that is, a pixel indicated by a dotted line in FIG. 2B) is restored. For example, the pixel Y of the second hierarchy deleted by thinning ₁₁ Is:
[Equation 3]

It is restored by performing an operation such as Similarly, all the thinned out pixels are restored using the upper layer pixels generated by the averaging and the pixels used for the generation of the upper layer pixels and not thinned out.
[0034]
The synthesizing circuit 170 inserts the second-layer restored pixel data D159 generated in this way into a predetermined position in the second-layer thinned-out decoded data D157 to synthesize the second-layer decoded image data D160. Form. Then, the second layer decoded image data D160 is sent to a television monitor having a medium number of display pixels via an output terminal, for example, and also sent to the pixel generation circuit 169.
[0035]
The pixel generation circuit 169 uses the second-layer decoded image data D160 and the first-layer thinned-out decoded data D156 to perform the first thinning performed by the thinning circuit 142 illustrated in FIG. 1 described above. A hierarchical pixel (that is, a pixel indicated by a dotted line in FIG. 2C) is restored. For example, the first layer pixel X deleted by thinning ₁₁ Is:
[Expression 4]

It is restored by performing an operation such as Similarly, all the thinned out pixels are restored using the upper layer pixels generated by the averaging and the pixels used for the generation of the upper layer pixels and not thinned out.
[0036]
The synthesizing circuit 168 inserts the first-layer restored pixel data D161 generated in this way into a predetermined position in the first-layer thinned-out decoded data D156, and synthesizes the first-layer decoded image data D162. Form. Then, the first layer decoded image data D162 is sent to the high-vision television monitor having a large number of display pixels, for example, via the output terminal.
[0037]
In the above configuration, the image signal encoding device 140 generates upper layer pixels based on an average value of a plurality of lower layer pixels, thereby generating multiple layers of image data D131, D133, and D135.
[0038]
In addition to this, issue The encoding device 140 can restore one pixel out of the pixels used for the same average calculation for the hierarchical image data excluding the highest layer, that is, the third layer, by a simple arithmetic operation on the decoding side. exclude. As a result, the image signal encoding device 140 can realize a hierarchical encoding process that does not involve an increase in the number of transmission pixels due to the hierarchical structure.
[0039]
By the way, in the image signal encoding device 140, each hierarchical image data is converted by the requantization circuits 147 to 149. Re The amount of data in each layer is compressed by quantization. As a result, each Re The quantized data D138, D139, and D140 inevitably have values including a quantization error at the time of requantization. As the quantization error increases, the decoded image data D158, D160, and D162 have an error larger than the true value, and the image quality deteriorates.
[0040]
Therefore, the influence of quantization errors in each layer in the image signal encoding device 140 and the image signal decoding device 160 will be considered. Where each pixel Z ₁₁ , Y ₁₁ , ... ₁₁ ', Y ₁₁ ′,… And set the true value to Z ₁₁ , Y ₁₁ , ..., and the quantization error is E (Z ₁₁ ), E (Y ₁₁ )..., For example, the third-layer pixel Z obtained by the inverse quantization circuit 167 ₁₁ Decryption value Z of ₁₁ ′ Is the following formula:
[Equation 5]

It becomes. Further, the second-layer pixel Y obtained by the inverse quantization circuit 166 ₁₃ , Y ₃₁ , Y ₃₃ Decrypted value Y of ₁₃ ', Y ₃₁ ', Y ₃₃ ′ Is the following formula:
[Formula 6]

It becomes.
[0041]
However, the second layer pixel Y restored by the pixel generation circuit 171. ₁₁ Is generated based on the equation (3), so the decoded value Y ₁₁ ′ Is the following formula:
[Expression 7]

Z ₁₁ The quantization error with respect to increases by a factor of four.
[0042]
Further, the first layer pixel X obtained by the inverse quantization circuit 165 is used. ₁₂ , X _{twenty one} , X _{twenty two} , X ₁₄ , X _{twenty three} , X _{twenty four} Decrypted value X of ₁₂ ', X _{twenty one} ', X _{twenty two} ', X ₁₄ ', X _{twenty three} ', X _{twenty four} ′ Is the following formula:
[Equation 8]

The first layer pixel X restored by the pixel generation circuit 169 ₁₃ , X ₃₁ , X ₃₃ Is generated based on the equation (4), the decoded value X ₁₃ ', X ₃₁ ', X ₃₃ ′ Is the following formula:
[Equation 9]

And each decoded value X ₁₃ ', X ₃₁ ', X ₃₃ ′, Spatially corresponding second layer pixel Y ₁₃ , Y ₃₁ , Y ₃₃ That is, the quantization error for the corresponding upper layer pixel is affected by a factor of four.
[0043]
Further, the first layer pixel X restored by the pixel generation circuit 169 via the pixel generation circuit 171. ₁₁ The decoded value X ₁₁ ′ Is the following formula:
[Expression 10]

As shown in FIG. ₁₁ ′, The second layer pixel Y ₁₃ , Y ₃₁ , Y ₃₃ In addition to the fact that the quantization error with respect to increases by a factor of 4, the third layer pixel Z ₁₁ As a result, the quantization error with respect to increases by 16 times.
[0044]
FIG. 5 shows each decoded pixel value Z ₁₁ ', Y ₁₁ ', Y ₁₃ Each quantization error E (Z ₁₁ ), E (Y ₁₃ ), E (Y ₃₁ ), ... shows the magnitude of the influence. As is apparent from FIG. 5, the quantization error in the upper layer greatly affects the decoded value in the lower layer.
[0045]
Considering this, in the first embodiment of the present invention, the pixel Z of the highest hierarchy ₁₁ Based on the polarity of the quantization error when quantizing ₁₁ Lower hierarchical pixel Y spatially corresponding to ₁₃ , Y ₃₁ , Y ₃₃ , X ₁₂ , X _{twenty one} , X _{twenty two} Quantization of the pixel Z of the highest hierarchy whose quantization error polarity is ₁₁ Is controlled to be the same as the polarity of the quantization error when quantizing. That is, for example, as is apparent from the equation (7), the second layer pixel Y is obtained by the inverse process of the average calculation. ₁₁ Z, which is an upper layer pixel when decoding ₁₁ Quantization error E (Z ₁₁ ) And Y in the same hierarchy (second hierarchy) (pixels existing in the same block) ₁₃ , Y ₃₁ , Y ₃₃ Quantization error E (Y ₁₃ ), E (Y ₃₁ ), E (Y ₃₃ ) Will be included. However, Z, which is a higher layer pixel ₁₁ Quantization error E (Z ₁₁ Y which is the same layer pixel as) ₁₃ , Y ₃₁ , Y ₃₃ Quantization error E (Y ₁₃ ), E (Y ₃₁ ), E (Y ₃₃ ) Is a relationship that cancels out, as is clear from the equation (7).
[0046]
Therefore, Z that is the upper layer pixel ₁₁ Quantization error E (Z ₁₁ Y which is the same layer pixel as) ₁₃ , Y ₃₁ , Y ₃₃ Quantization error E (Y ₁₃ ), E (Y ₃₁ ), E (Y ₃₃ ) Have the same polarity, the quantization error can be reduced during decoding. Therefore, according to the first embodiment of the present invention, as is apparent from the equation (7), decoding is performed by quantizing the lower layer so that it has the same polarity as the highest layer during encoding. In some cases, quantization errors cancel each other, and image quality degradation in lower layers can be reduced.
[0047]
Similarly, as apparent from the equation (10), the first layer pixel X is obtained by the inverse process of the average calculation. ₁₁ Z, which is a pixel in the highest hierarchy (third hierarchy) ₁₁ Quantization error E (Z ₁₁ ) And the upper layer (second layer) Y ₁₃ , Y ₃₁ , Y ₃₃ Quantization error E (Y ₁₃ ), E (Y ₁₃ ), E (Y ₃₃ ) And the same level (first level) pixels (pixels existing in the same block) ₁₂ , X _{twenty one} , X _{twenty two} Quantization error E (X ₁₂ ), E (X _{twenty one} ), E (X _{twenty two} ) Will be included. However, the highest hierarchical pixel Z ₁₁ Quantization error E (Z ₁₁ ) And Y which is the upper hierarchy ₁₃ , Y ₃₁ , Y ₃₃ Quantization error E (Y ₁₃ ), E (Y ₁₃ ), E (Y ₃₃ ) And X which is a pixel in the same hierarchy ₁₂ , X _{twenty one} , X _{twenty two} Quantization error E (X ₁₂ ), E (X _{twenty one} ), E (X _{twenty two} ) Is a canceling relationship, as is clear from the equation (10).
[0048]
Therefore, Z is the highest hierarchical pixel. ₁₁ Quantization error E (Z ₁₁ ) And Y which is the upper hierarchy ₁₃ , Y ₃₁ , Y ₃₃ Quantization error E (Y ₁₃ ), E (Y ₁₃ ), E (Y ₃₃ ) And X which is a pixel in the same hierarchy ₁₂ , X _{twenty one} , X _{twenty two} Quantization error E (X ₁₂ ), E (X _{twenty one} ), E (X _{twenty two} ) Have the same polarity, the quantization error can be reduced during decoding. Therefore, according to the first embodiment of the present invention, as is clear from the equation (10), decoding is performed by quantizing the lower layer so that it has the same polarity as the highest layer during encoding. In some cases, quantization errors cancel each other, and image quality degradation in lower layers can be reduced.
[0049]
As described above, the image signal encoding device 140 can perform quantization processing in consideration of the quantization error propagating from the upper layer to the lower layer on the decoding side, thereby reducing image quality degradation based on the quantization error. It has been made so that it can.
[0050]
According to the configuration of the first embodiment described above, pixel data Y for one pixel among a plurality of lower layer pixels used for the same average value calculation to generate one pixel of the upper layer. ₁₁ , Y ₁₅ , ..., X ₁₁ , X ₁₃ ,... Are not transmitted, and quantization characteristics when quantizing a lower layer pixel corresponding to the highest layer pixel according to the polarity of the quantization error when the highest layer pixel is quantized Is controlled so that the quantization error is the same as the polarity of the quantization error when the highest layer pixel is quantized, so that compression efficiency can be improved and image quality degradation can be reduced.
[0051]
(2) Second embodiment
FIG. 6 shows an image signal encoding device 180 according to the second embodiment as a whole. Compared with the first embodiment, it has the same configuration as the image signal encoding device 140 of FIG. 1 except that the residual (difference) compression encoding of inter-layer data is performed except for the highest layer. Accordingly, parts corresponding to those in FIG.
[0052]
That is, the image signal encoding device 140 of the first embodiment transmits each pixel in the form of PCM (Pulse Code Modulation), whereas the image signal encoding device 180 of the second embodiment. Each pixel is transmitted in the form of DPCM (Differential Pulse Code Modulation). Therefore, the image signal encoding device 180 can further reduce the amount of transmission information.
[0053]
More specifically, the image signal encoding device 180 supplies the third hierarchy image data D135 and the second hierarchy block data D134 to the difference circuit 181. Then, the difference circuit 181 calculates the difference between the spatially corresponding pixels between the third layer image data D135 and the second layer blocking data D134 to form second layer difference data D170. The second hierarchy difference data D170 is sent to the thinning circuit 182. At this time, the difference circuit 181 determines that the second layer pixel Y ₁₃ , Y ₃₁ , Y ₃₃ Difference value ΔY ₁₃ , ΔY ₃₁ , ΔY ₃₃ , The upper layer pixel Z corresponding to these pixels ₁₁ Using the following formula,
## EQU11 ##

It asks like this.
[0054]
Similarly, the image signal encoding device 180 supplies the second hierarchy block data D134 and the first hierarchy block data D132 to the difference circuit 183. The difference circuit 183 calculates the difference between the spatially corresponding pixels between the second hierarchy block data D134 and the first hierarchy block data D132 to form the first hierarchy difference data D171. The one-layer difference data D171 is sent to the thinning circuit 184. At this time, the difference circuit 183 generates the first layer pixel X ₁₂ , X _{twenty one} , X _{twenty two} Difference value ΔX ₁₂ , ΔX _{twenty one} , ΔX _{twenty two} , The upper layer pixel Y corresponding to these pixels ₁₁ Using the following formula,
[Expression 12]

It asks like this.
[0055]
Similarly to the thinning circuits 142 and 145 shown in FIG. 1 described above, the thinning circuits 184 and 182 receive the blocked data D132 from the blocking circuit 141 and the blocked data D134 from the blocking circuit 144, respectively. Then, corresponding to the block data D132 and D134 composed of 4 pixels, one pixel is thinned out from the first layer and second layer difference data D171 and D170 composed of 4 pixels for each block, Hierarchical difference subtraction data D172 and D173 constituted by the remaining three pixels excluding one pixel removed per block are formed, and the hierarchical difference subtraction data D172 and D173 are sent to the quantization circuits 185 and 186.
[0056]
The third-layer quantization circuit 187 receives the third-layer image data from the averaging circuit 146 and quantizes each pixel to, for example, 2 bits in accordance with the minimum distortion criterion as in the first embodiment. . Then, the quantization circuit 187 sends a quantization error information signal S11 indicating whether the quantization error is positive or negative to the quantization control circuit 210.
[0057]
Here, the first-level quantization circuit 185 and the second-level quantization circuit 186 have the same quantization error polarity as that of the third-level (highest-level) quantization circuit 187, as in the first embodiment. Accordingly, the quantization characteristics are controlled based on the quantization control signals S12 and S13 output from the quantization control circuit 210. That is, when the polarity of the quantization error by the quantization circuit 187 of the upper layer pixel is positive, the quantization circuit 185 for quantizing the lower layer pixel spatially corresponding to the upper layer pixel and The quantization characteristic of 186 is controlled so that the polarity of the quantization error is positive. When the polarity of the quantization error by the quantization circuit 187 for the upper layer pixel is negative, the quantization circuit 185 for quantizing the lower layer pixel spatially corresponding to the upper layer pixel and The quantization characteristic of 186 is controlled so that the polarity of the quantization error is negative.
[0058]
The requantized data D174, D175, and D176 obtained by the quantization circuits 185, 186, and 187 are variable length encoded by variable length encoding circuits (VLC) 150, 151, and 152, and the first layer, The data is output as the second and third layer encoded data D177, D178, and D179. Then, these first layer, second layer and third layer encoded data D177, D178, D179 are input to the transmission format conversion circuit 153, and the transmission format conversion circuit 153 forms the transmission image data D180, Output it. The output transmission image data D180 is then supplied to the receiving side via the communication path 188 or recorded on a recording medium 189 such as a disk, tape, or semiconductor memory via the recording transmission path.
[0059]
The image signal decoding apparatus 190 that decodes the transmission image data D144 formed in this way can be configured as shown in FIG. 7, for example. In the image signal decoding device 190, the same reference numerals are given to the corresponding parts to the image signal decoding device 160 shown in FIG. The image signal decoding device 190 inputs the transmission image data D180 supplied from the communication path 188 or reproduced from the recording medium 189 via the reproduction transmission path to the data diversion circuit 161. The data diversion circuit 161 divides the transmission image data D180 into first layer, second layer, and third layer encoded data D181, D182, and D183, and these first layer, second layer, and third layer encoded data. D181, D182 and D183 are supplied to variable length decoding circuits (IVLC) 162, 163 and 164, respectively.
[0060]
Each of the variable length decoding circuits (IVLC) 162, 162, and 164 performs variable length decoding on the first layer, second layer, and third layer encoded data D181, D182, and D183, respectively, and re-quantized data D184, D185. , D186, and the re-quantized data D184, D185, D186 are sent to the inverse quantization circuits 191, 192, and 193, respectively. Note that the variable-length decoding circuits (IVLC) 162, 163, and 164 perform inverse processing corresponding to the variable-length coding circuits (VLC) 150, 151, and 152 shown in FIG.
[0061]
The inverse quantization circuits 191, 192 and 193 dequantize the requantized data D184, D185 and D186, which are requantized to 2 bits per pixel, into data consisting of 8 bits per pixel, respectively. And second layer difference subtraction data D187 and D188 and third layer decoded image data D189 are generated. Note that the inverse quantization circuits 191, 192, and 193 execute inverse processing corresponding to the quantization circuits 185, 186, and 187 shown in FIG. 6, respectively.
[0062]
Third-layer decoded image data D189 is output as it is to a low-resolution television monitor or the like, and is also transmitted to addition circuit 194 and pixel generation circuit 195. The adder circuit 194 has the following formula:
[Formula 13]

The second layer decimation data D190 is calculated by performing the addition operation as described above.
[0063]
The pixel generation circuit 195 uses the second hierarchical difference thinning data D188 and the third hierarchical decoded image data D189 to perform the second hierarchical pixel Y thinned out by the thinning circuit 182 shown in FIG. ₁₁ With the following formula:
[Expression 14]

Ask for. Compared with the above-described equation (3), this equation (14) is the third layer pixel Z ₁₁ It can be seen that the multiplication coefficient of (4) is “4” in the equation (3), whereas it is “1” in this equation. This means that the influence of the pixel value of the third layer on the pixel value of the second layer is smaller in the equation (14) than the equation (3).
[0064]
The synthesizing circuit 196 synthesizes the second layer deciphered decoded data D190 and the second layer restored pixel data D191 to form second layer decoded image data D192, and this second layer decoded image data D192 is output via the output terminal. In addition to outputting to a television monitor or the like, the data is sent to an addition circuit 197 and a pixel generation circuit 198. The adder circuit 197 has the following formula:
[Expression 15]

The first layer decimation data D193 is calculated by performing the addition operation as described above.
[0065]
The pixel generation circuit 198 uses the first layer difference subtraction data D187 and the second layer decoded image data D192 to perform the first layer pixel X thinned out by the thinning circuit 184 shown in FIG. ₁₃ , X ₃₁ , X ₃₃ With the following formula:
[Expression 16]

Ask for. In addition, the pixel generation circuit 198 includes the thinned first layer pixel X. ₁₁ With the following formula:
[Expression 17]

Ask for.
[0066]
The synthesizing circuit 199 synthesizes the first layer deciphered decoded data D193 and the first layer restored pixel data D194 to form first layer decoded image data D195. Then, the first layer decoded image data D195 is output to, for example, a high-resolution television monitor via an output terminal.
[0067]
Next, as in the first embodiment, the influence of quantization error in each layer in the image signal encoding device 180 and the image signal decoding device 190 of the second embodiment will be considered.
Third-layer pixel Z obtained by inverse quantization circuit 193 ₁₁ Decryption value Z of ₁₁ ′ Is the same as the equation (5). Further, the second-layer pixel Y obtained by the adder circuit 194 ₁₃ , Y ₃₁ , Y ₃₃ Decrypted value Y of ₁₃ ', Y ₃₁ ', Y ₃₃ ′ Is the following formula:
[Formula 18]

It becomes the value shown by.
[0068]
In addition, the second layer pixel Y restored by the pixel generation circuit 195 ₁₁ Is generated based on the equation (14), so the decoded value Y ₁₁ ′ Is the following formula:
[Equation 19]

It becomes the value shown by. As described above, the image signal encoding apparatus 180 according to the second embodiment transmits the difference data between the layers as the transmission data except for the highest layer data, and the equation (19) is described above as (7). Compared with the equation, the third layer pixel Z ₁₁ Quantization error E (Z ₁₁ ) Has a multiplication coefficient of “4” in equation (7), whereas “ 1 "
[0069]
This means that according to the encoding / decoding of the second embodiment, the quantization error of the third layer pixel has an influence on the decoding of the second layer pixel. 1/4 It means that it can be reduced to the extent. That is, in the first embodiment, as apparent from the equation (19), the difference between the hierarchies is calculated. ₁₁ The quantization error of is the decoded pixel value Y of the second layer ₁₁ ', Y ₁₃ ', Y ₃₁ ', Y ₃₃ It will be reflected in all of '. Therefore, the influence of the quantization error of the third layer pixel on the decoding of the second layer pixel can be reduced.
[0070]
Further, the first layer pixel X obtained by the adder circuit 197 is used. ₁₂ , X ₂₁ , X ₂₂ , X ₃₂ , X ₄₁ , X ₄₂ Decrypted value X of ₁₂ ', X ₂₁ ', X ₂₂ ', X ₃₂ ', X ₄₁ ', X ₄₂ ′ Is the following formula:
[Expression 20]

The first layer pixel X is restored by the pixel generation circuit 198. ₃₁ Decrypted value X of ₃₁ ′ Is the following formula:
[Expression 21]

The value indicated by.
[0071]
Further, the first layer pixel X restored by the pixel generation circuit 198 via the pixel generation circuit 195. ₁₁ Decrypted value X of ₁₁ ′ Is the following formula:
[Expression 22]

The value indicated by ₁₁ Quantization error about etc Y is affected, Y ₁₃ , Y ₃₁ , Y ₃₃ Quantization error about Etc. It will be doubled. However, as is clear from a comparison of the equations (22) and (10), Z ₁₁ , Y ₁₃ , Y ₃₁ , Y ₃₃ Is the decoded value X ₁₁ The influence on ′ is significantly reduced as compared with the case of the first embodiment. That is, in the first embodiment, for example, as is apparent from the equation (10), the pixel Z of the third hierarchy is ₁₁ Quantization error and second layer pixel Y ₁₃ , Y ₃₁ , Y ₃₃ The quantization error of is the decoded pixel value X of the first layer ₁₁ ′ Only, and the decoded pixel X of the first layer ₁₂ ', X ₂₁ ', X ₂₂ It is not reflected in ′.
[0072]
However, in the second embodiment, as apparent from the equation (22), the difference between the hierarchies is calculated. ₁₁ Quantization error and second layer pixel Y ₁₃ , Y ₃₁ , Y ₃₃ The quantization error of the first-level decoded pixel X ₁₁ ', X ₁₂ ', X _{twenty one} It will be reflected in ′. Therefore, the influence of the quantization error of the third layer pixel and the quantization error of the second layer pixel on the decoding of the first layer pixel can be reduced.
[0073]
Therefore, according to the configuration of the image signal encoding device of the second embodiment described above, each hierarchical data of a plurality of hierarchical image data obtained by the average value calculation from the input image data D131 and the adjacent upper hierarchical data In the image signal encoding device 180 that generates hierarchical difference data and quantizes the highest hierarchy data D135 and the plurality of hierarchy difference data D172 and D173, respectively, to generate a plurality of hierarchically encoded data, each hierarchy except the highest hierarchy Pixel data ΔY that can be restored by an arithmetic operation using adjacent lower-layer pixels and pixels of its own layer ₁₁ , ΔY ₁₅ , ..., ΔX ₁₁ , ΔX ₁₃ , ... are not transmitted, and the quantization characteristics when quantizing the lower layer pixel corresponding to the highest layer pixel according to the polarity of the quantization error when the highest layer pixel is quantized Is controlled so that the quantization error has the same polarity as the quantization error when the highest layer pixel is quantized, so that the compression efficiency can be further improved in a state in which the image quality deterioration is suppressed.
[0074]
(3) Third embodiment
FIG. 8 shows an image signal encoding apparatus 400 according to the third embodiment as a whole. The image signal encoding device 400 has a configuration similar to that of the image signal encoding device 180 of the second embodiment, except that adaptive prediction circuits 401 and 402 are provided, compared to the second embodiment. Therefore, the same reference numerals are given to the corresponding parts in FIG.
[0075]
The adaptive prediction circuit 401 performs a predetermined prediction process based on the third layer image data D135, and generates second layer prediction data D400 corresponding to the second layer image data D134. Then, the second layer prediction data is sent to the difference circuit 181. Similarly, the adaptive prediction circuit 402 performs predetermined prediction processing based on the second layer image data D134, and generates first layer prediction data D401 corresponding to the first layer image data D132. Then, the first layer prediction data is sent to the difference circuit 183.
[0076]
In practice, the adaptive prediction circuits 401 and 402 apply class classification adaptive processing to predict one pixel in the lower layer from a plurality of upper layer pixels. Specifically, the lower layer pixels to be predicted are classified based on the level distribution of a plurality of upper layer pixels spatially nearby. The adaptive prediction circuits 401 and 402 have a memory (not shown) that stores a plurality of prediction coefficients or one prediction value for each class, which has been acquired in advance by learning, and is determined by the above class classification. A plurality of prediction coefficients or one prediction value corresponding to the selected class is read from the memory. In the case of a prediction value, the prediction value is used as it is as a prediction pixel. In the case of a prediction coefficient, a prediction value is generated by linear linear combination of a plurality of prediction coefficients and a plurality of pixels.
[0077]
Further, when the predicted value is normalized, the predicted value is generated by performing a predetermined process on the predicted value. Details of such class classification adaptation processing are disclosed, for example, in Japanese Patent Application No. 4-155719. Such an algorithm for adaptive classification processing is already known. In the adaptive prediction circuit of the third embodiment, an algorithm for class classification adaptive processing is used. However, the present invention is not limited to this, and other currently used prediction methods may be used.
[0078]
FIG. 9 shows the configuration of an image signal decoding device 190 ′ that decodes transmission image data D180 ′ that has been compression-encoded by the image signal encoding device 400. This image signal decoding device 190 ′ is different from the image signal decoding device 190 of the second embodiment in that the image signal decoding of the second embodiment is provided except that adaptive prediction circuits 401 ′ and 402 ′ are provided. The configuration is the same as that of the device 190. Therefore, the same reference numerals are given to the corresponding parts to FIG.
[0079]
In the image signal decoding apparatus 190 ′ according to the third embodiment, the first adaptive prediction circuit 401 ′ to which the third layer decoded data D189 ′ is input is the class classification adaptive corresponding to the adaptive prediction circuit 401 shown in FIG. The process is executed based on the third layer decoded data D189 ′, and the second layer prediction data D400 ′ obtained as a result is sent to the pixel generation circuit 195. The pixel generation circuit 195 uses the second hierarchy difference subtraction data D188 ′ and the second hierarchy prediction data D400 ′ output from the second hierarchy inverse quantization circuit 192, and performs the decimation circuit 182 shown in FIG. A thinned second layer pixel is generated. Also, the second layer prediction data D400 ′ obtained by the first adaptive prediction circuit 401 ′ based on the third layer decoding data D189 ′ is output from the second-layer inverse quantization circuit 192. It is added to the subtraction data D188 'for the hierarchy difference. The second layer deciphered decoded data D190 ′ obtained by this addition is combined with the second layer pixel D191 ′ generated by the pixel generation circuit 95 to become second layer decoded image data D192 ′.
[0080]
In addition, the second adaptive prediction circuit 402 ′ to which the second layer decoded data D192 ′ is input executes the class classification adaptive processing corresponding to the applied prediction circuit 402 shown in FIG. 8 based on the second layer decoded data D192 ′. Then, the first layer prediction data D401 ′ obtained as a result is sent to the pixel generation circuit 198. The pixel generation circuit 198 uses the first hierarchy difference subtraction data D187 ′ and the first hierarchy prediction data D401 ′ output from the first hierarchy inverse quantization circuit 191 to perform the decimation circuit 184 shown in FIG. A thinned first layer pixel is generated.
[0081]
Also, the first layer prediction data D401 ′ obtained by the second adaptive prediction circuit 402 ′ based on the second layer decoded data D192 ′ is the first layer output from the first layer inverse quantization circuit 191. It is added to the subtraction data D187 'for the hierarchy difference. The first layer deciphered decoded data D193 ′ obtained by this addition is combined with the first layer pixel D194 ′ generated by the pixel generation circuit 198 to become the first layer decoded image data D195 ′.
[0082]
According to the configuration of the third embodiment described above, the quantization at the time of quantizing the lower layer pixel corresponding to the highest layer pixel according to the polarity of the quantization error when the highest layer pixel is quantized. By controlling the characteristics so that the quantization error is the same as the polarity of the quantization error when the highest layer is quantized, the compression efficiency can be improved and the image quality degradation can be reduced. Further, by using the adaptive prediction circuits 401 and 402, the residuals of the second layer difference data D170 ′ and the first layer difference data D171 ′ obtained from the difference circuits 181 and 183, respectively, can be further reduced. The image signal encoding device 400 that can further reduce the amount of transmission information can be realized.
[0083]
(4) Fourth embodiment
In the fourth embodiment, as described above in the first to third embodiments, spatially corresponds to the highest layer pixel according to the characteristics of the quantization error when the highest layer pixel is quantized. In addition to controlling the quantization characteristics when quantizing lower layer pixels so that the quantization error is the same as the polarity of the quantization error when quantizing the highest layer pixel, The quantization circuit increases the number of quantization bits (decreases the quantization width) and performs fine quantization. In this way, in addition to the effects of the first to third embodiments, the image quality degradation at the time of decoding can be further reduced.
[0084]
In the case of the fourth embodiment, in the image signal encoding device 140 described above with respect to the first embodiment, the quantization circuit 147 performs 1-bit quantization, and the quantization circuit 148 performs 4-bit quantization. The quantization characteristics of the quantization circuits 147 to 149 are controlled so that the quantization circuit 149 performs 16-bit quantization. In this case, the number of quantization bits is selected in consideration of the degree of influence of quantization error in the upper layer on the restored pixel value when the lower layer data is restored.
[0085]
As a result, for example, considering the above-described equation (10), the quantization error E (Z ₁₁ ) Error degree is the quantization error E (X ₁₂ ), E (X _{twenty one} ), E (X _{twenty two} ), And the quantization error E (Y ₁₃ ), E (Y ₃₁ ), E (Y ₃₃ ) Is the quantization error E (X ₁₂ ), E (X _{twenty one} ), E (X _{twenty two} ) In comparison with quantization error E (Z ₁₁ ) Is multiplied by 16 or the quantization error E (Y ₁₃ ), E (Y ₃₁ ), E (Y ₃₃ ) Is multiplied by 4, the resulting error is the quantization error E (X ₁₂ ), E (X _{twenty one} ), E (X _{twenty two} ). Therefore, the image quality degradation of the lower layer image based on the quantization distortion in the upper layer can be remarkably reduced.
[0086]
Further, the degree of influence of the quantization error of the upper layer data on the lower layer data is related to the number of layers from the lowest layer and the number of pixels used when generating the upper layer data. Therefore, when determining the number of quantization bits in the upper layer, the quantization that affects the lower layer depends on the number of layers from the lowest layer and the number of pixels used when generating the upper layer data. By setting the number of quantization bits to minimize the error or the number of quantization bits larger than that, it is possible to provide an image coding apparatus with reduced image quality degradation. In addition, if the number of quantization bits in the upper layer is increased in this way, the amount of transmitted information seems to increase accordingly, but since the number of transmission pixels is smaller in the upper layer, the increase in the amount of information by increasing the number of quantization bits is It is suppressed to such an extent that it does not actually cause a problem.
[0087]
In the image signal encoding devices 180 and 400 described above for the second and third embodiments, the quantization circuit 185 performs 1-bit quantization, and the quantization circuit 186 performs 2-bit quantization. The quantization characteristics of the quantization circuits 185 to 187 are controlled so that the circuit 187 performs 4-bit quantization.
[0088]
In this way, the number of quantization bits assigned to each quantization circuit of the second and third embodiments is reduced with respect to the number of quantization bits assigned to each quantization circuit of the first embodiment. In the third embodiment, difference data between layers is transmitted except for the highest layer data. Therefore, as is clear from comparing the above-described expressions (3) and (14), (7) and (19), and (10) and (22), This is because the multiplication coefficient related to the quantization error at the time of restoration is smaller in the second and third embodiments than in the first embodiment. That is, the number of quantization bits is determined by the degree of influence of the quantization error given to the lower layer.
[0089]
(5) Other embodiments
In the above-described embodiment, the case has been described where hierarchical image data D131, D134, and D135 for three layers are generated and compressed and transmitted. However, the present invention is not limited to this, and the average value is sequentially calculated. The present invention can also be applied to the case where layer image data for four layers or five layers is generated by repeating the operation, and this is compressed and encoded by quantization and transmitted.
[0090]
Further, in the above-described embodiment, the case where one pixel of the upper layer is generated by the average value calculation using the four pixels of the lower layer has been described. However, the present invention is not limited to this. Hierarchical image data may be generated by generating one pixel in the upper hierarchy by an average value calculation using pixels or more pixels.
[0091]
In the fourth embodiment described above, the number of quantization bits of the quantization circuits 47, 48, and 49 is set to 1 bit, 4 bits, and 16 bits, respectively, and the quantization bits of the quantization circuits 85, 86, and 87 are each set to 1. Although the case of bits, 2 bits, and 4 bits has been described, the present invention is not limited to this, and in short, the quantization circuits in higher layers may be controlled to have a smaller quantization width.
[0092]
In the above-described embodiments, all quantizers are described as linear quantizers. However, the present invention is not limited to this, and is applicable to nonlinear quantization, adaptive quantization, and dynamic range. Quantization or the like may be applied.
Furthermore, although the embodiments of the present invention are realized by the hardware shown using the block diagram, the present invention is not limited to this, and can also be realized by software using a CPU or a memory. It is.
[0093]
Various modifications and application examples can be considered without departing from the gist of the present invention. Therefore, the gist of the present invention is not limited to the examples.
[0094]
【The invention's effect】
As described above, according to the present invention, for a plurality of hierarchical image data generated by the average value calculation, one pixel among the plurality of lower layer pixels used for the same average value calculation in order to generate one pixel of the upper layer. Quantization error when the pixel data of the highest layer is quantized The polarity of whether the value is positive or negative Quantization when quantizing lower layer pixel data spatially corresponding to the highest layer pixel Error polarity Is controlled to be the same as the polarity of the quantization error when quantizing the highest layer pixel data, it is possible to realize hierarchical encoding with improved compression efficiency and reduced image quality degradation.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an image signal encoding apparatus according to a first embodiment.
FIG. 2 is a schematic diagram for explaining hierarchization and transmission pixels;
FIG. 3 is a schematic diagram for explaining control of quantization characteristics;
FIG. 4 is a block diagram showing a configuration of an image signal decoding apparatus according to the first embodiment.
FIG. 5 is a chart showing the influence of quantization errors in each layer on the restored pixels in each layer.
FIG. 6 is a block diagram showing a configuration of an image signal encoding apparatus according to a second embodiment.
FIG. 7 is a block diagram showing a configuration of an image signal decoding apparatus according to a second embodiment.
FIG. 8 is a block diagram showing a configuration of an image signal encoding device according to a third embodiment.
FIG. 9 is a block diagram showing a configuration of an image signal decoding apparatus according to a third embodiment.
FIG. 10 is a block diagram showing a configuration of a conventional image signal encoding apparatus that realizes hierarchical encoding.
FIG. 11 is a block diagram showing the configuration of a conventional image signal decoding apparatus for decoding hierarchically encoded data.
[Explanation of symbols]
140, 180, 400... Image signal encoding device, 143, 146... Averaging circuit, 142, 145, 182, 184... Thinning circuit, 147 to 149, 185 to 187. ... Image signal decoding apparatus, 401, 402, 401 ′, 402 ′... Adaptive prediction circuit, 200... Quantization control circuit, D131 ... Input image data, D133 ... Second layer image data, D135. 3rd layer image data, D141, D177, D177 '... 1st layer encoded data, D142, D178, D178' ... 2nd layer encoded data, D143, D179, D179 '... 3rd layer encoded data , D144, D180, D180 ′... Transmission image data, D158, D189... Third layer decoded image data, D160, D192. Layer decoded image data, D162, D195 ... First layer decoded image data, D170, D170 '... Second layer difference data, D171, D171' ... First layer difference data, D400 ... Second layer prediction data, D401: First layer prediction data, S1: Quantization error information signal, S2, S3: Quantization control signal, Z: Third layer pixel, Y: Second layer pixel, X: First layer Pixel.

Claims (10)

In an image signal encoding method for generating a plurality of hierarchical image data having different resolutions from input image data and encoding each hierarchical image data,
A step of averaging a plurality of pixel values of each hierarchical image data to generate upper hierarchical image data;
For each layer image data except the highest layer having the lowest resolution, pixel data for one pixel among a plurality of lower layer pixels used for the same average value calculation to generate one pixel of the upper layer is thinned out, and the rest A step of forming decimation data formed by the pixels of
A quantization step for compressing and encoding the thinned data of each layer excluding the highest layer image data and the highest layer by quantization, and generating a plurality of layer encoded data;
Consists of
In the quantization step, spatially corresponds to the highest layer pixel according to the polarity indicating whether the quantization error when the pixel data of the highest layer is quantized is a positive value or a negative value. The quantization characteristics when quantizing lower layer pixel data to be quantized are controlled so that the quantization error is the same as the polarity of the quantization error when the highest layer pixel data is quantized. An image signal encoding method. In an image signal encoding method for generating a plurality of hierarchical image data having different resolutions from input image data and encoding each hierarchical image data,
A step of averaging a plurality of pixel values of each hierarchical image data to generate upper hierarchical image data;
For each layer image data excluding the highest layer having the lowest resolution, a step of calculating a difference between each layer image data and the adjacent upper layer image data to form layer difference data;
With respect to the hierarchical difference data of each layer, the difference pixel data that can be restored by arithmetic operation using the difference data of the adjacent upper layer and the difference data of the own layer is thinned to form thinned data formed by the remaining pixels. Steps,
A quantization step for compressing and encoding the thinned data of each layer excluding the highest layer image data and the highest layer by quantization, and generating a plurality of layer encoded data;
Consists of
In the quantization step, a lower layer corresponding to the highest layer pixel is determined according to a polarity indicating whether a quantization error when the pixel data of the highest layer is quantized is a positive value or a negative value. An image signal characterized by controlling the quantization characteristics when quantizing the pixel data so that the quantization error is the same as the polarity of the quantization error when the top layer pixel data is quantized. Encoding method. In an image signal encoding device for generating a plurality of hierarchical image data having different resolutions from input image data and encoding each hierarchical image data,
Image data generating means for averaging a plurality of pixel values of each hierarchical image data and generating higher hierarchical image data;
For each layer image data except the highest layer having the lowest resolution, pixel data for one pixel among a plurality of lower layer pixels used for the same average value calculation to generate one pixel of the upper layer is thinned out, and the rest Thinned data forming means for forming thinned data formed by the pixels;
Quantization means for compressing and encoding the thinned data of each layer excluding the highest layer image data and the highest layer by quantization to generate a plurality of layer encoded data,
Consists of
The quantization means spatially corresponds to the highest layer pixel according to the polarity indicating whether the quantization error when quantizing the pixel data of the highest layer is a positive value or a negative value. The quantization characteristics when quantizing lower layer pixel data to be quantized are controlled so that the quantization error is the same as the polarity of the quantization error when the highest layer pixel data is quantized. An image signal encoding device. In claim 3,
The quantization means further quantizes the data of the upper layer more finely. In an image signal encoding device for generating a plurality of hierarchical image data having different resolutions from input image data and encoding each hierarchical image data,
Image data generating means for averaging a plurality of pixel values of each hierarchical image data and generating higher hierarchical image data;
For each layer image data excluding the highest layer data with the lowest resolution, a difference data forming unit that calculates a difference between each layer image data and the adjacent upper layer image data and forms layer difference data;
With respect to the hierarchical difference data of each layer, the difference pixel data that can be restored by the arithmetic operation using the difference data of the adjacent upper layer and the difference data of the own layer is thinned, and the thinned data formed by the remaining pixels is formed. Thinning data forming means;
Quantization means for compressing and encoding the thinned data of each layer excluding the highest layer image data and the highest layer by quantization to generate a plurality of layer encoded data,
Consists of
The quantization means has a lower layer corresponding to the highest layer pixel according to a polarity indicating whether a quantization error when the pixel data of the highest layer is quantized is a positive value or a negative value. An image signal characterized by controlling the quantization characteristics when quantizing the pixel data so that the quantization error is the same as the polarity of the quantization error when the top layer pixel data is quantized. Encoding device. In claim 5,
In the above quantization means, the higher-level data is further quantized more finely. In claim 5,
The difference data forming means for forming the hierarchy difference data obtains a difference between each of the hierarchy image data and the adjacent lower hierarchy image data predicted and generated by a predetermined prediction calculation process using the adjacent upper hierarchy image data. Thus, the hierarchical difference data is formed. In an image signal transmission method for generating a plurality of hierarchical image data having different resolutions from input image data, encoding each hierarchical image data, and transmitting the encoded data,
A step of averaging a plurality of pixel values of each hierarchical image data to generate upper hierarchical image data;
For each layer image data except the highest layer having the lowest resolution, pixel data for one pixel among a plurality of lower layer pixels used for the same average value calculation to generate one pixel of the upper layer is thinned out, and the rest A step of forming decimation data formed by the pixels of
A quantization step for compressing and encoding the thinned data of each layer excluding the top layer image data and the top layer by quantization, and generating a plurality of layer encoded data as transmission image data;
A step of transmitting the transmission image data;
Consists of
In the quantization step, spatially corresponds to the highest layer pixel according to the polarity indicating whether the quantization error when the pixel data of the highest layer is quantized is a positive value or a negative value. The quantization characteristics when quantizing lower layer pixel data to be quantized are controlled so that the quantization error is the same as the polarity of the quantization error when the highest layer pixel data is quantized. Image signal transmission method. In an image signal transmission method for generating a plurality of layer image data having different resolutions from input image data, encoding each layer image data, and transmitting the encoded data, an average operation is performed on a plurality of pixel values of each layer image data. , A step of generating upper layer image data,
For each layer image data excluding the highest layer data having the lowest resolution, a step of calculating a difference between each layer image data and the adjacent upper layer image data to form layer difference data;
With respect to the hierarchical difference data of each layer, the difference pixel data that can be restored by the arithmetic operation using the difference data of the adjacent upper layer and the difference data of the own layer is thinned, and the thinned data formed by the remaining pixels is formed. Steps,
A quantization step for compressing and encoding the thinned data of each layer excluding the top layer image data and the top layer by quantization, and generating a plurality of layer encoded data as transmission image data;
A step of transmitting the transmission image data;
Consists of
In the quantization step, a lower layer corresponding to the highest layer pixel is determined according to a polarity indicating whether a quantization error when the pixel data of the highest layer is quantized is a positive value or a negative value. An image signal characterized by controlling the quantization characteristics when quantizing the pixel data so that the quantization error is the same as the polarity of the quantization error when the top layer pixel data is quantized. Transmission method. In an image signal encoding device for generating a plurality of hierarchical image data having different resolutions from input image data and encoding each hierarchical image data,
Image data generating means for generating data related to the upper layer image based on a plurality of pixel values of each layer image data;
With respect to the data related to each hierarchical image except the highest resolution having the lowest resolution, the data related to each hierarchical level is thinned out within the range that can be restored by the calculation using the data related to each hierarchical level and the data related to the adjacent upper hierarchical level, and the remaining pixels. Decimation data forming means for forming decimation data formed by data relating to,
Quantization means for compressing and encoding the data relating to the highest hierarchical image and the thinned data relating to each layer excluding the highest hierarchical level by quantization, and generating a plurality of hierarchically encoded data,
Consists of
In the quantization means, spatially applied to the highest layer pixel according to the polarity indicating whether the quantization error when the data related to the pixel of the highest layer is quantized is positive or negative. Control the quantization characteristics when quantizing the data for the corresponding lower layer pixels so that the quantization error is the same as the polarity of the quantization error when the data for the uppermost layer pixels is quantized. An image signal encoding apparatus characterized by the above.

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