JPH07108018B2 - Color image coding device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image coding apparatus for coding multivalued color image information captured by a color original reading apparatus, a color TV camera or the like.

[0002]

2. Description of the Related Art Conventionally, in transmitting and storing image information, it is general to consider the efficiency and suppress redundancy by encoding. In such encoding, most of the target image information is binary white / black or color information.

[0003]

However, in recent years, multi-valued image information has been developed and high definition has been attempted, and multi-valued color has also been used.

Therefore, it is necessary to perform coding on multi-valued color image information as well.
The conventional white / black method is applied to each of the three primary colors of R (red), G (green), and B (blue), or each pixel is quantized by utilizing the color correlation between the RGB three primary colors. Etc. are considered. The former method is naturally inefficient,
Moreover, in some cases, it may cause color misregistration. Further, in the latter case, color shift is unlikely to occur, but high efficiency cannot be expected because the RGB three primary colors have too strong a correlation.

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional example, and an object thereof is to provide a color image encoding apparatus capable of encoding color image information efficiently and with good color reproducibility. It is what

[0006]

In order to solve the above-mentioned problems, a color image coding apparatus according to the present invention comprises an input means for inputting a plurality of color component signals, and a plurality of colors input from the input means. Separation means for separating the lightness signal and the color signal from the component signal, a conversion means for orthogonally converting the lightness signal for each block of a predetermined size and outputting a conversion coefficient, and a DC component of the conversion coefficient for encoding a DC component. 1 encoding means, second encoding means for encoding an AC component of the conversion coefficient, extraction means for extracting a representative value for each block of a predetermined size for the color signal, and extraction by the extraction means And a third encoding unit that encodes the representative value of the generated color signal.

[0007]

The present invention will be described in detail below with reference to preferred embodiments.

First, the outline of the encoding of color image information according to the present invention will be described. R (red), G (green),
The three primary colors of B (blue) have weaker correlation between signals, and
The signal is converted into a signal form that can be separated into lightness information and color information, and the signal is further cut into small blocks. For each block, the lightness within the block, the structural information regarding the edge within the block, and the color information within the block are expressed. It is to be encoded into an information array.

FIG. 1 shows the basic concept of encoding color image information. That is, the R, G, and B signals are first processed as CIE1 as an example of a signal form having a small signal correlation.
976 uniform color space converted into L ^* a ^* b ^* signal, and the information in the small block is composed of three elements of L (brightness), S (structure information) and C (color information) shown in FIG. To be encoded.

FIG. 2 shows RGB → L ^* a in the target image.
^{The state of *} b ^* conversion and cutout of a square block of 4 pixels × 4 pixels is shown. Reference numeral 201 is a document, and reference numeral 202 is a block, and blocks are sequentially cut out in 4 × 4 size from the corners of the document. Further, 203 is one of the blocks, and shows a case where the block includes an edge portion.

FIG. 2B shows the state of the three primary colors (R, G, B) forming the block 203 when the characters written on the original 201 are red, and the RGB three primary colors are as shown in the figure. Similarly, the edge appears only in R.

FIG. 2C shows the RGB shown in FIG. 2B.
The case where the signal is converted into L ^* a ^* b ^* is shown.

Here, the conversion formula for converting RGB to L ^* a ^* b ^* signals is shown below.

[0014]

[Outer 1] Than this

[0015]

[Outside 2]

FIG. 3 shows an embodiment of a circuit configuration for achieving the encoding shown in FIG. Reference numeral 301 denotes RGB sequentially input line by line from a color scanner or the like.
It is a 4-line buffer that temporarily stores the signal in order to cut it into the above-mentioned blocks. That is, once the 4-line buffer 301
The 4 × 4 block is cut out by reading out the signals of 4 lines stored in the 4 × 4 size. 302
Is an L ^* a ^* b ^* conversion unit that performs RGB → L ^* a ^* b ^* conversion, and performs a conversion operation based on the conversion formula shown above.

FIG. 4 shows a specific example of the L ^* a ^* b ^* conversion unit 302, in which the memory tables 401, 402, and 403 in which the conversion tables for L ^* a ^* b ^* are written are stored in R.
It is realized by a look-up table method accessed by a GB signal. In this way, the RGB signal is converted into an L ^* a ^* b ^* signal having a small signal correlation.

Numeral 303 indicates from the L ^* a ^* b ^* conversion section 302 that X ₁₁ , X ₁₂ , and L ₁₂ in the L ^* block of FIG.
... X _21, X _22, is output.., In the order of X ₄₄ L ^*
It is a signal. Reference numeral 304 denotes an orthogonal transform unit that performs an orthogonal transform on the L ^* signal, and its method is Hadamard (Hadamar).
d) Transform, discrete CoS transform and the like. This orthogonal transformation is performed for each block in order to extract the form of the edge included in the block, which makes the subsequent quantization process efficient.

The expression of the quadratic Hadamard transform is shown below as an example of the orthogonal transform.

The second-order Hadamard transform is

[0021]

[Outside 3] Can be expressed as here,

[0022]

[Outside 4] Then, the above formula is

[0023]

[Outside 5] And, for example,

[0024]

[Outside 6] Becomes

FIG. 5 shows a specific example in which the Hadamard transform is used in the orthogonal transform unit 304. Reference numeral 410 is a Hadamard matrix address generator that generates an address in the row direction when performing a matrix operation. 411, 412, 4
13 In the above equation, a circuit for by entering X _ij to generate a Y _11, 411 is a look-up table and outputting the multiplying coefficients of the Hadamard matrix to the input X _ij, 412 lookup The adder 413 that adds the outputs of the table 411 adds 1/4 to the addition result of the adder 412.
It is a 1/4 divider that multiplies by. Below, 415-417
Is a circuit which similarly inputs X _ij to generate Y ₄₄ .
Then, by inputting X _ij , Y ₁₁ to Y ₁₄ , Y _{21 to} Y ₂₄ , and Y _31.
There are a total of 16 circuits for outputting .about.Y ₃₄ and Y _{41 to} Y ₄₄ . That is, it exists for each Y _ij and the following operations are executed respectively.

[0026]

[Outside 7]

In FIG. 3, 305 is Y ₁₁ in the output of the orthogonal transformation unit 304, and the value of this Y ₁₁ represents a DC component close to the average value of Y _ij for each block, which is the brightness of the block. Is a coefficient representing. A quantizer 307 quantizes Y ₁₁ and quantizes 10-bit Y ₁₁ into 8 bits, and outputs L (brightness) 308.

Reference numeral 306 denotes fifteen Y ₁₂ to Y ₄₄ other than Y _11.
Is a coefficient representative of the structure of the edge included in the block, and is coded into 12 bits by the quantizer 309, that is, the structure information 310 is rounded to a predetermined 409b type pattern. Becomes As a result, the structure information 310 represents the form of the edge included in each block.

311 and 312 are averaging circuits that take the respective averages a ^* and b ^* in each block of a ^* and b ^* which are the outputs of the L ^* a ^* b ^* converter 302, and are adder and divider. Composed of.

A quantizer 313 collectively quantizes the block average values of a ^* b ^* , and quantizes them to 12 bits. Thereby, the color information 314 of each block is formed.

It is known that if any of the quantizers 307, 309, and 313 are usually vector quantizers, the efficiency is good.

Reference numeral 315 is a multiplexer for collecting L (brightness) 308, S (structure) 310, and C (color information) 314 obtained as described above into one code for each block. Reference numeral 316 is the output signal of the multiplexer 315, that is, the encoded code shown in FIG.

In this way, the RGB signals input from the color scanner or the like are converted into L ^* a ^* b ^* signals having a small signal correlation for each unit block of a predetermined size, and this L ^* a ^* is converted ^.
The color image of each block is represented by lightness, structure and color information based on the b ^* signal.

By decoding the code encoded in this way,
When a color image is reproduced, each area divided by the edge of each block according to the structure information is painted with a color represented by lightness and color information. As a result, the color original image is reproduced well.

In this embodiment, RGB signals are converted into L ^* a ^* b.
^As indicated by ^* , L ^* a ^* ν ^* , or NTSC YIQ,
It is also possible to use PAL, YUV, etc.

Further, the orthogonal transform is shown by Hadamard transform, but it is also possible to use discrete COS transform, slant transform, or the like.

Although the quantizer is described as vector quantizer, it is not particularly limited. The bit allocation of L, S, and C is not limited to that shown in the embodiment.

The input signal is not limited to RGB, and depending on the sensor, Y (yellow) G (green) C (cyan) or the like may be input.

Further, a ^* b ^* is represented by an average value, but it may be stored in more detail.

[0040]

As described above, according to the color image coding apparatus of the present invention, efficient coding can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a data array after being encoded.

FIG. 2 is a diagram showing a state of block cutout and signal conversion.

FIG. 3 is a block diagram of an embodiment for performing encoding according to the present invention.

FIG. 4 is a diagram showing a configuration example of an L ^* a ^* b ^* conversion unit.

FIG. 5 is a diagram showing a configuration example of an orthogonal transformation unit.

[Explanation of symbols]

301 4 line buffer 302 L ^* a ^* b ^* converter 304 Orthogonal converter 311, 312 Average circuit 307, 309, 313 Quantizer 315 Multiplexer

Claims (1)

[Claims] 1. An input unit for inputting a plurality of color component signals, a separating unit for separating a lightness signal and a color signal from the plurality of color component signals input from the input unit, and a block of a predetermined size for the lightness signal. Transform means for performing orthogonal transform for each and outputting transform coefficients, first coding means for coding a DC component of the transform coefficients, and second coding for coding an AC component of the transform coefficients. Means for extracting the representative value of the color signal for each block of a predetermined size, and a third encoding means for encoding the representative value of the color signal extracted by the extracting means. And a color image encoding device.