JP2642524B2 - Image intra-frame encoder and decoder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intra-frame encoder and decoder for an image using an orthogonal transform.

[0002]

2. Description of the Related Art Documents relating to such an intra-frame image coding and decoding apparatus include the following. Document name: Yukito Tsuboi Teiji Okamoto, "Comparative study of various methods of entropy coding in color still image coding", (PCSJ87), September 25-27, 1987
FIG. 2 shows a configuration diagram of a conventional intra-frame encoding method of an image. In FIG. 2, an image signal input from a television camera 201 or the like is digitized in an A / D converter 202. Since a general television camera performs interlaced scanning, the interlaced / non-interlaced converter 203 converts the interlaced scanning into non-interlaced scanning in preparation for the subsequent frame processing, and outputs the converted data to the blocking circuit 204.

In the interlace / non-interlace conversion unit 203, one frame is composed of two fields as shown in FIG. The blocking circuit 204 divides each frame into blocks of N × N pixels, and inputs each block component to the orthogonal transformation unit 205. Orthogonal transformation unit 2
At 05, orthogonal transform processing such as discrete cosine transform is performed, and each transform coefficient is quantized by the quantizer 206. The quantized value obtained by the quantizer 206 is
7 and is transmitted to the receiving side.

On the receiving side, the received code is subjected to Huffman in a variable length decoding unit 208, inversely quantized in an inverse quantization unit 209, inversely orthogonally transformed in an inverse orthogonal transformation unit 210, and output to a framing circuit 211. The reproduced signal of each block is reconstructed into a frame by the framing circuit 211, and converted from non-interlaced scanning to interlaced scanning by the non-interlace / interlace converter 212. After that, the signal is returned to an analog signal by the D / A converter 213 and displayed as a reproduced image on a monitor.

[0005]

In intra-frame encoding using orthogonal transform such as discrete cosine transform, one frame is composed of two fields by interlace / non-interlace conversion as preprocessing of an encoding unit. After that, it is encoded by the encoding unit. At this time, due to the difference in the scanning time between the fields, the image between the lines becomes discontinuous in the moving part as shown in FIG. Originally, in image coding that combines orthogonal transform and variable-length coding, the aim is to reduce the coding rate by utilizing the fact that power is concentrated on the low-frequency components of orthogonal transform coefficients. Due to the cause, a signal component in a high frequency in the vertical direction in the moving region may be strongly generated. This causes a problem that the code amount increases. Accordingly, an object of the present invention is to provide an intra-frame encoding using an orthogonal transform such as a discrete cosine transform.
An object of the present invention is to reduce a transmission rate by suppressing a high frequency component in a vertical direction of a conversion coefficient generated by a difference in scanning time between fields in a moving region and improving power concentration on a low frequency coefficient.

[0006]

According to the present invention, there is provided an intra-frame encoder which performs an orthogonal transformation for each block on a normal frame image, and a line transform for each field in each block. And an encoding unit that performs an orthogonal transformation for each block on the frame image that has been subjected to the line transformation. The image processing apparatus further includes means for selecting image data having a smaller code amount from image data generated from the two encoding units, and transmitting the selected image data together with an identification signal indicating which is selected. Further, the intra-frame decoder of the present invention has a decoding unit corresponding to each encoding unit.

[0007]

FIG. 5 is an explanatory diagram of the line conversion. FIG. 5 shows a frame image of one block, in which pixel components in the first field are indicated by solid lines and pixel components in the second field are indicated by dotted lines. The normal frame image referred to in this specification corresponds to the block on the left side of FIG. 5, and means a frame image in which pixels for two fields are arranged in the order of the line positions in each block unit. Further, the frame image of the line conversion referred to in this specification corresponds to the block on the right side of FIG. 5. In each block unit, the frame image is first grouped for each field, and the frames arranged in the line order in the field are arranged. Means an image. In the present invention,
For both the normal frame image and the line image of the frame image, orthogonal transformation is performed for each block, and the smaller code amount is selected. Therefore, it is expected that the image with less discontinuity between the lines is selected, and that the high-frequency component in the vertical direction is suppressed. As a result, the signal power of the coefficient on the high frequency side of the transform coefficient can be reduced, and the amount of code generated from the encoder can be reduced.

[0008]

FIG. 1 shows the configuration of an intraframe encoder and decoder for an image signal according to the present invention. In FIG. 1, an image signal input from a television camera 101 or the like is digitized by an A / D converter 102, scan-converted from two fields into a one-frame image by an interlace / non-interlace converter 103, and further divided into a blocking circuit 104. Is divided into blocks of N × N pixels. Each block component Xij (i = 1 to N, j = 1 to
N) are input to two types of encoding units a and b. In the encoding unit a, each block component Xij is orthogonally transformed by the orthogonal transformer 105, and the transform coefficient is
After the encoding in step 6, the quantized value of the coefficient is run-length encoded in the variable length encoding unit 107 to obtain a code Ia.

On the other hand, each block component Xij converted by the encoding unit b is line-converted by the line conversion unit 108 for every N × N pixels as shown in FIG. Thereafter, the orthogonal transformer 109
Then, the transform coefficient is quantized by the quantizer 110, and then the variable-length encoding unit 111 performs run-length encoding on the quantized value of the coefficient to obtain the code Ib. The codes Ia and Ib are compared in code amount by the rate comparison circuit 112, the code with the smaller code amount is selected, and sent out to the transmission line together with the identification signal k indicating which one is selected.
On the receiving side, the code transmitted from the identification signal k is Ia or Ia.
b is determined, and is input to the decoding unit da in the case of Ia and to the decoding unit db in the case of Ia.

In the decoding unit da, the code Ia is run-length decoded by the variable length decoding unit 113,
After the inverse quantization in step 4, the inverse orthogonal transform is performed by the inverse orthogonal transformer 115 to obtain Xaij. Further, in the decoding unit db, the code Ib is run-length decoded by the variable length decoding unit 116, inversely quantized by the inverse quantizer 117, inversely orthogonally transformed by the inverse orthogonal transformer 118, and then transformed by the line inverse transformation unit 119. Return the line to its original position and get Xbij. Xaij or Xbij is converted to the framing circuit 120 by the identification signal k.
Is converted into a frame by a non-interlace / interlace converter 121, converted into an analog signal by a D / A converter 122, and displayed on a monitor 123.

[0011]

According to the present invention, the power of the high frequency side of the transform coefficients obtained by the orthogonal transformation is suppressed by performing the line transformation for each block before the orthogonal transformation in the moving part of the image. Further, in this configuration, the resolution in the time direction is not impaired. In addition, in consideration of such a difference in scanning time between fields, encoding may be performed for each field. However, an encoder performing such block processing has a characteristic block-like deterioration. Sometimes, in an actual reproduced image viewed on a monitor, the image appears as a block having twice the size in the vertical direction. However, in the method shown in the present invention, the deterioration does not spread beyond the size of the block which is the processing unit.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an intra-frame encoder and a decoder according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a conventional technique.

FIG. 3 is an explanatory diagram of interlace / non-interlace conversion.

FIG. 4 is an explanatory diagram of a contour portion of a moving area.

FIG. 5 is an explanatory diagram of line conversion according to the present invention.

[Explanation of symbols]

 Reference Signs List 101 TV camera 102 A / D conversion unit 103 Interlace / non-interlace conversion unit 104 Blocking circuit 105 Orthogonal conversion operation unit 106 Quantizer 107 Variable length encoder 108 Line conversion circuit 109 Orthogonal conversion operation unit 110 Quantizer 111 Variable Length Encoder 112 Rate Comparison Circuit 113 Variable Length Decoder 114 Inverse Quantizer 115 Inverse Orthogonal Transform Operation Circuit 116 Variable Length Decoder 117 Inverse Quantizer 118 Inverse Orthogonal Transform Operation Circuit 119 Line Inverse Transform Circuit 120 Frame conversion circuit 121 Non-interlace / interlace conversion unit 122 D / A converter 123 Monitor

Claims (2)

(57) [Claims] 1. A first encoding unit that performs orthogonal transform on a block-by-block basis for a normal frame image, and performs a line transform on a field-by-field basis on a block-by-block basis.
For the frame image that has been subjected to the line conversion, a second encoding unit that performs an orthogonal transformation and image data generated from the two encoding units that have a smaller code amount are selected for each block. Means for transmitting the selected signal together with an identification signal indicating the selected one. 2. An apparatus for decoding image data encoded by the intra-frame encoder according to claim 1, wherein the first decoder corresponds to the first encoder, and the second decoder corresponds to the first encoder. A second decoding unit corresponding to the encoding unit, and means for adaptively switching between the two decoding units to perform decoding by an identification signal sent from the intra-frame encoder. An intra-frame decoder for an image.