Picture encoder and picture decoder

• US 6,263,024 B1
• Filed: 08/06/1998
• Issued: 07/17/2001
• Est. Priority Date: 12/12/1996
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Matsumoto, Taisuke
• Primary Examiner(s): Le, Vu
• Application Number:
  US09/117,543
• Time in Patent Office: 1,076 Days
• Field of Search: 375/240.12, 375/240.16, 375/240.21, 348/400.1, 348/402.1, 348/407.1, 348/413.1, 348/416.1, 348/426.1, 348/405.1, 386/111, 358/430, 382/237, 382/238
• US Class Current: 375/240.16
• CPC Class Codes: H04N 19/112 according to a given display mode, e.g. for interlaced or progressive display mode
• CPC Class Codes: H04N 19/13 Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
• CPC Class Codes: H04N 19/16 for a given display mode, e.g. for interlaced or progressive display mode
• CPC Class Codes: H04N 19/20 using video object coding
• CPC Class Codes: H04N 19/59 involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Abstract

In an image coding apparatus which uses as an input a binary digital image with an interlaced structure in which one frame comprises two fields and codes said image by dividing it into two-dimensional blocks made up of a plurality of pixels for each block, the method for carrying out coding in field units or frame units is judged for each block and coding is performed in field units or frame units according to the mode judgment result for each block. Furthermore, in an image decoding apparatus which decodes for each block a binary digital image with an interlaced structure in which one frame comprises two fields from the image coding signal coded by said image coding apparatus, decoding processing is carried out in field units or frame units according to the mode information.

Claims

1. An image coding apparatus, comprising:

a field-unit processing section that down-samples a pixel block on a field-by-field basis, said pixel block already obtained by dividing a binary digital image;

a frame-unit processing section that down-samples the pixel block on a frame-by-frame basis;

a mode judging section that judges for each block whether to down-sample the pixel block on the field-by-field basis or on the frame-by-frame basis when said binary digital image is coded and outputs mode information indicating the judgment result; and

a switching section that switches input or output to/from said field-unit processing section and said frame-unit processing section according to the mode information.

2. An image coding apparatus, comprising:

a field-unit processing section that processes a pixel block on a field-by-field basis, said pixel block already obtained by dividing a binary digital image;

a frame-unit processing section that processes the pixel block on a frame-by-frame basis;

a mode judging section that judges on a block-by-block basis whether to process said pixel block on the field-by-field basis or on the frame-by-frame basis; and

a switching section that switches input or output to/from said field-unit processing section and said frame-unit processing section according to mode information indicating the judgment result of said mode judging section,

wherein said field-unit processing section comprises;

a field change point detecting section that detects a pixel value change point in a field image;

a field predicting section that predicts a next pixel value change point based on the pixel value change point previously detected in the same field image;

a field coding section that codes a difference value between the pixel value change point detected by said field change point detecting section and a next pixel value change point predicted by said field prediction section to output a coded image signal; and

said frame-unit processing section comprises;

a frame change point detecting section that detects a pixel value change point in the frame image;

a frame predicting section that predicts the next pixel value change point based on the pixel value change point previously detected in the same frame image;

a frame coding section that codes a difference value between the pixel value change point detected by said frame change point detecting section and the next pixel value change point predicted by said frame predicting section to output a coded image signal; and

wherein said mode judging section compares a code length of the coded image signal output from said field coding section with a code length of the coded image signal output from said frame coding section in order to determine a mode to be used.

3. An image coding apparatus, comprising:

a field-unit processing section including a field-surveying section that surveys a pixel value distribution status of already coded pixels peripheral to a target pixel in a field image;

a field-determining section that determines a probability distribution of the pixel value of said target pixel from the pixel value distribution status; and

a field-arithmetically-coding section that performs an arithmetic coding on the pixel value of said target pixel according to said determined probability distribution;

a frame-unit processing section including a frame-surveying section that surveys a pixel value distribution status of already coded pixels peripheral to a target pixel in a frame image;

a frame-determining section that determines a probability distribution of the pixel value of said target pixel from the distribution status; and

a field-arithmetically-coding section that performs an arithmetic coding on the pixel value of said target pixel according to said determined probability distribution;

a mode judging section that judges on a block-by-block basis whether to process said pixel block on the field-by-field basis or on the frame-by-frame basis; and

a switching section that switches input or output to/from said field-unit processing section and said frame-unit processing section according to mode information indicating the judgment result of said mode judging section.

4. The image coding apparatus according to claim 3, wherein said field-unit processing section includes a field motion compensation section that performs motion compensation on the pixel block on the field-by-field basis to generate a field predicted image, and provides the field predicted image substitute for the field image to said field-surveying section for surveying the pixel value distribution status, and said frame-unit processing section includes a frame motion compensation section that performs motion compensation on the pixel block on the frame-by-frame basis to generate a frame predicted image, and provides the frame predicted image substitute for the frame image to said frame-surveying section for surveying the pixel value distribution status.

5. An image coding apparatus, comprising:

a field-unit processing section that codes a color digital image and a binary digital image indicating a significant form of said color digital image on a field-by-field basis;

a frame-unit processing section that codes the color digital image and the binary digital image indicating the significant form of said color digital image on a frame-by-frame basis;

a mode judging section that determines whether to perform coding on said color digital image on the field-by-field basis or on the frame-by-frame basis and outputs mode information indicating the judgment result; and

a switching section that switches input or output to/from said field-unit processing section and said frame-unit processing section according to mode information indicating the judgment result of said mode judging section.

6. An image coding apparatus, comprising:

a field-unit processing section that codes a color digital image and a binary digital image indicating a significant form of said color digital image on a field-by-field basis;

a frame-unit processing section that codes the color digital image and the binary digital image indicating the significant form of said color digital image on a frame-by-frame basis;

a mode judging section that determines whether to perform coding on said binary digital image on the field-by-field basis or on the frame-by-frame basis and outputs mode information indicating the judgment result; and

a switching section that switches input or output to/from said field-unit processing section and said frame-unit processing section according to mode information indicating the judgment result of said mode judging section.

7. An image decoding apparatus, comprising:

a field-unit processing section that up-samples a coded image signal on a field-by-field basis;

said coded image signal already coded on the field-by-field basis in an image coding apparatus;

a frame-unit processing section that up-samples a coded image signal on a frame-by-frame basis, said coded image signal already coded on the frame-by-frame basis in the image coding apparatus;

a switching section that switches input or output to/from said field-unit processing section and said frame-unit processing section according to mode information indicating whether the coding is performed on the field-by-field basis or on the frame-by-frame basis in the image coding apparatus.

8. An image decoding apparatus, comprising:

a difference value decoding section that decodes a coded image signal of a difference value between a detected pixel value change point and a predicted pixel value change point in a pixel block to obtain a decoded difference value, said coded image signal being coded on a field-by-field basis or on a frame-by-frame basis in an image coding apparatus, said pixel block already obtained by dividing a binary digital image;

a predicting section that predicts a next pixel value change point based on a decoded pixel value change position previously in the pixel block;

an adding section that adds said decoded difference value to the predicted next pixel value change point;

a field-unit processing section that restores a field image from the addition result output from said adding section on the field-by-field basis;

a frame-unit processing section that restores a frame image from the addition result output by said adding section on the frame-by-frame basis; and

a switching section that switches input or output to/from said field-unit processing section and said frame-unit processing section according to mode information indicating whether the coding is performed on the field-by-field basis or on the frame-by-frame basis in the image coding apparatus.

9. An image decoding apparatus, comprising:

a probability distribution determining section that determines a probability distribution of a pixel value of a target pixel based on a distribution of pixel values peripheral to the target pixel;

an arithmetic decoding section that decodes an arithmetic-coded image signal from the probability distribution of the target pixel to generate a decoded image;

a field-unit processing section that surveys a pixel value distribution of pixels peripheral to the target pixel on a field-by-field basis from the decoded image previously decoded and outputs the pixel value distribution as the survey result to said probability distribution determining section;

a frame-unit processing section that surveys the pixel value distribution of pixels peripheral to the target pixel on a frame-by-frame basis from the decoded image previously decoded and outputs the pixel value distribution as the survey result to said probability distribution determining section; and

a switching section that switches input or output to/from said field-unit processing section and said frame-unit processing section according to mode information indicating whether the coding is performed on the field-by-field basis or on the frame-by-frame basis in the image coding apparatus.

10. An image decoding apparatus comprising:

a probability distribution determining section that determines a probability distribution of a pixel value of a target pixel based on a distribution of pixel values peripheral to the target pixel;

an arithmetic decoding section that decodes an arithmetic-coded image signal from the probability distribution of the target pixel to generate a decoded image;

a field-unit processing section having a field motion compensation section that performs a motion compensation on a field-by-field basis on a pixel block to be decoded in the decoded image to generate a field prediction image, and a field-surveying section that surveys a pixel value distribution status of already decoded pixels peripheral to the target pixel in said field prediction image;

a frame-unit processing section having a frame motion compensation section that performs a motion compensation on a frame-by-frame basis on the pixel block to be decoded in the decoded image to generate a frame prediction image, and a frame-surveying section that surveys the pixel value distribution status of already decoded pixels peripheral to the target pixel in said frame prediction image; and

a switching section that switches input or output to/from said field-unit processing section and said frame-unit processing section according to mode information indicating whether the coding is performed on the field-by-field basis or on the frame-by-frame basis in the image coding apparatus.

11. An image decoding apparatus, comprising:

a field-unit processing section having a color image field decoding section that decodes a color digital image on a field-by-field basis, and a binary image field decoding section that decodes a binary digital image indicating a significant form of said color digital image on a field-by-field basis;

a frame-unit processing section having a color image frame decoding section that decodes said color digital image on the frame-by-frame basis, and a binary image frame decoding section that decodes the binary digital image indicating the significant form of said color digital image on the frame-by-frame basis; and

a switching section that switches input or output to/from said field-unit processing section and said frame-unit processing section according to mode information indicating whether the coding for the color digital image is performed on the field-by-field basis or on the frame-by-frame basis in the image coding apparatus.

12. An image decoding apparatus, comprising:

a field-unit processing section having a color image field decoding section that decodes a color digital image on a field-by-field basis, and a binary image field decoding section that decodes a binary digital image indicating a significant form of said color digital image on a field-by-field basis;

a frame-unit processing section having a color image frame decoding section that decodes said color digital image on the frame-by-frame basis, and a binary image frame decoding section that decodes the binary digital image indicating the significant form of said color digital image on the frame-by-frame basis; and

a switching section that switches input or output to/from said field-unit processing section and said frame-unit processing section according to mode information indicating whether the coding for the binary digital image is performed on the field-by-field basis or on the frame-by-frame basis in the image coding apparatus.

13. An apparatus for coding an image and decoding a coded image comprising a coding device and a decoding device,

said coding device includes:

a first field-unit processing section that down-samples a pixel block on a field-by-field basis, said pixel block already obtained by dividing a binary digital image;

a first frame-unit processing section that down-samples the pixel block on a frame-by-frame basis;

a mode judging section that judges for the each block whether to down-sample the pixel block on the field-by-field basis or on the frame-by-frame basis when said binary digital image is coded and outputs mode information indicating the judgment result; and

a first switching section that switches input or output to/from said first field-unit processing section and said first frame-unit processing section according to the mode information,

said decoding device includes;

a second field-unit processing section that up-samples a coded image signal on a field-by-field basis;

said coded image signal already coded on the field-by-field basis in an image coding apparatus;

a second frame-unit processing section that up-samples a coded image signal on the frame-by-frame basis, said coded image signal already coded on the frame-by-frame basis in the image coding apparatus;

a second switching section that switches input or output to/from said second field-unit processing section and said second frame-unit processing section according to mode information indicating whether the coding is performed on the field-by-field basis or on the frame-by-frame basis in the image coding apparatus.

14. An apparatus for coding an image and decoding a coded image comprising a coding device and a decoding device,

said coding device includes:

a first field-unit processing section includes a field-surveying section that surveys a pixel value distribution status of already coded pixels peripheral to a target pixel in the field image;

a field-determining section that determines a probability distribution of the pixel value of said target pixel from the pixel value distribution status; and

a field-arithmetically-coding section that performs an arithmetic coding on the pixel value of said target pixel according to said determined probability distribution;

a first frame-unit processing section includes a frame-surveying section that surveys a pixel value distribution status of already coded pixels peripheral to a target pixel in a frame image;

a frame-determining section that determines a probability distribution of the pixel value of said target pixel from the distribution status; and

a field-arithmetically-coding section that performs an arithmetic coding on the pixel value of said target pixel according to said determined probability distribution;

a mode judging section that judges on a block-by-block basis whether to process said pixel block on the field-by-field basis or on the frame-by-frame basis; and

a first switching section that switches input or output to/from said first field-unit processing section and said first frame-unit processing section according to mode information indicating the judgment result of said mode judging section;

said decoding device includes;

a probability distribution determining section that determines a probability distribution of a pixel value of a target pixel based on a distribution of pixel values peripheral to the target pixel;

an arithmetic decoding section that decodes an arithmetic-coded image signal from the probability distribution of the target pixel to generate a decoded image;

a second field-unit processing section that surveys a pixel value distribution of pixels peripheral to the target pixel on a field-by-field basis from the decoded image previously decoded and outputs the pixel value distribution as the survey result to said probability distribution determining section;

a second frame-unit processing section surveys the pixel value distribution of pixels peripheral to the target pixel on a frame-by-frame basis from the decoded image previously decoded and outputs the pixel value distribution as the survey result to said probability distribution determining section; and

a second switching section that switches input or output to/from said second field-unit processing section and said second frame-unit processing section according to mode information indicating whether the coding is performed on the field-by-field basis or on the frame-by-frame basis in the image coding apparatus.

15. An apparatus according to claim 14, wherein said first field-unit processing section includes a field motion compensation section that performs a motion compensation on the pixel block on the field-by-field basis to generate a field predicted image, and provides the field predicted image substitute for the field image to said field-surveying section for surveying the pixel value distribution status, and said second frame-unit processing section includes a frame motion compensation section that performs a motion compensation on the pixel block on the frame-by-frame basis to generate a frame predicted image, and provides the frame predicted image substitute for the frame image to said frame-surveying section for surveying the pixel value distribution status,

said second field-unit processing section performs a motion compensation on a field-by-field basis on a pixel block to be decoded in the decoded image to generate a field prediction image, and surveys the pixel value distribution status in said field prediction image substitute for the decoded image decoded by said arithmetic decoding section; and said second frame-unit processing section performs a motion compensation on a frame-by-frame basis on a pixel block to be decoded in the decoded image to generate a frame prediction image, and surveys the pixel value distribution status in said frame prediction image substitute for the decoded image decoded by said arithmetic decoding section.

16. A recording medium that can be read by a computer, which stores the following programs in executable format:

a first program instruction means for making a computer processor down-sample a pixel block on a field-by-field basis obtained by dividing a binary digital image;

a second program instruction means for making the computer processor down-sample said pixel block on a frame-by-frame basis;

a third program instruction means for making the computer processor judge for each block whether to down-sample said pixel block on the field-by-field basis or on the frame-by-frame basis when coding said binary digital image;

a fourth program instruction means for making the computer processor select which is more effective, down-sampling on the field-by-field basis or down-sampling on the frame-by-frame basis.

17. A recording medium that can be read by a computer, which stores the followings programs in executable format:

a first program instruction means for making a computer processor up-sample a coded image signal on a field-by-field basis;

a second program instruction means for making the computer processor up-sample a coded image signal on a frame-by-frame basis;

a third program instruction means for making the computer processor select up-sampling in more effective mode according to mode information indicating a coding mode which is used to down-sample a pixel block on the field-by-field basis or on the frame-by-frame basis.

18. A recording medium that can be read by a computer, which stores the following programs in executable format:

a first program instruction means for making a computer processor judge a coding mode for each pixel block whether on a field-by-field basis or on the frame-by-frame basis when coding a binary digital image;

a second program instruction means for making the computer processor survey a pixel value distribution status of already coded pixels peripheral to the target pixel in a field image;

a third program instruction means for making the computer processor determine a probability distribution regarding the pixel value of said target pixel from the pixel value distribution status that appears in said survey result;

a fourth program instruction means for making the computer processor arithmetically code the pixel value of said target pixel according to said determined probability distribution;

a fifth program instruction means for making the computer processor survey a pixel value distribution status of already coded pixels peripheral to the target pixel in a frame image;

a sixth program instruction means for making the computer processor determine a probability distribution regarding the pixel value of said target pixel from the pixel value distribution status that appears in said survey result;

a seventh program instruction means for making the computer processor arithmetically code the pixel value of said target pixel according to said determined probability distribution;

an eighth program instruction means for making the computer processor select which is a more effective mode, arithmetic coding on the field-by-field basis or arithmetic coding on the frame-by-frame basis according to the mode information indicating whether to code said pixel block on the field-by-field basis or on the frame-by-frame basis.

19. A recording medium that can be read by a computer, which stores the following programs in executable format:

a first program instruction means for surveying a pixel value distribution of pixels peripheral to the target pixel on the field-by-field basis from a previously decoded image;

a second program instruction means for surveying the pixel value distribution of pixels peripheral to the target pixel on the frame-by-frame basis from the decoded image;

a third program instruction means for making the computer processor select effective pixel value distribution of pixels peripheral to the target pixel according to mode information indicating a coding mode which is used to code a pixel block whether on the field-by-field basis or on the frame-by-frame basis;

a fourth program instruction means for making the computer processor determine the probability distribution of pixel value of said target pixel based on the selected effective pixel value distribution;

a fifth program instruction means for making the computer processor decode an arithmetically coded image signal of said target pixel using the probability distribution of said determined target pixel.

20. An image coding method, comprising:

down-sampling a pixel block on a field-by-field basis, said pixel block already obtained by dividing a binary digital image;

down-sampling the pixel block on a frame-by-frame basis;

judging for each pixel block whether to down-sample the pixel block on the field-by-field basis or on the frame-by-frame basis when said binary digital image is coded;

outputting mode information indicating the judgment result; and

switching to/from down-sampling in the field-by-field basis and in the frame-by-frame basis according to the mode information.

21. An image coding method, comprising:

processing a pixel block on a field-by-field basis, said pixel block already obtained by dividing a binary digital image;

processing the pixel block on a frame-by-frame basis;

judging on a block-by-block basis whether to process said pixel block on the field-by-field basis or on the frame-by-frame basis; and

switching processing to/from the field-by-field basis and the frame-by-frame basis according to mode information indicating the judgment result,

wherein said field-by-field processing comprises;

detecting a pixel value change point in a field image;

predicting a next pixel value change point based on the pixel value change point previously detected in the same field image;

coding a difference value between the detected pixel value change and the predicted next pixel value change point to output a coded image signal; and

said frame-by-frame processing comprises;

detecting a pixel value change point in the frame image;

predicting a next pixel value change point based on the pixel value change point previously detected in the same frame image;

coding a difference value between the detected pixel value change and the predicted next pixel value change point to output a coded image signal; and

wherein the judging compares a code length of the coded image signal output on the field-by-field basis with a code length of the coded image signal output on the frame-by-frame basis in order to determine a mode to be used.

22. An image coding method, comprising:

down-sampling a pixel block on a field-by-field basis, said pixel block already obtained by dividing a binary digital image;

surveying a first pixel value distribution status of already coded pixels peripheral to a target pixel in the field image;

determining a first probability distribution of the pixel value of said target pixel from the pixel value distribution status;

performing an arithmetic coding on the pixel value of said target pixel according to said determined first probability distribution;

down-sampling the pixel block on a frame-by-frame basis;

surveying a second pixel value distribution status of already coded pixels peripheral to a target pixel in a frame image;

determining a second probability distribution of the pixel value of the target pixel from the second distribution status;

performing an arithmetic coding on the pixel value of said target pixel according to said determined second probability distribution;

judging for each pixel block whether to down-sample the pixel block on the field-by-field basis or on the frame-by-frame basis when said binary digital image is coded;

outputting mode information indicating the judgment result; and

switching to/from down-sampling in the field-by-field basis and in the frame-by-frame basis according to the mode information.

23. The image coding method according to claim 22, wherein the field-by-field down-processing further comprises performing motion compensation on the pixel block on the field-by-field basis to generate a field predicted image, and providing the field predicted image substitute for the field image for surveying the pixel value distribution status;

and

the frame-by-frame down-sampling further comprises performing motion compensation on the pixel block on the frame-by-frame basis to generate a frame predicted image, and providing the frame predicted image substitute for the frame image for surveying the pixel value distribution status.

24. An image coding method, comprising:

coding a color digital image and a binary digital image indicating a significant form of the color digital image on a field-by-field basis;

coding a color digital image and a binary digital image indicating a significant form of the color digital image on a frame-by-frame basis;

determining whether to perform coding on the color digital image on the field-by-field basis or on the frame-by-frame basis and outputting mode information indicating the judgment result; and

switching between coding on a field-by-field basis and a frame-by-frame basis according to mode information indicating the judgment result.

25. An image coding method, comprising:

coding a color digital image and a binary digital image indicating a significant form of the color digital image on a field-by-field basis;

coding a color digital image and a binary digital image indicating a significant form of the color digital image on a frame-by-frame basis;

determining whether to perform coding on said binary digital image on the field-by-field basis or on the frame-by-frame basis and outputting mode information indicating the judgment result; and

a switching between coding on a field-by-field basis and a frame-by-frame basis according to mode information indicating the judgment result.

26. An image decoding method, comprising:

up-sampling a coded image signal on a field-by-field basis;

said coded image signal already coded on the field-by-field basis in an image coding apparatus;

up-sampling a coded image signal on a frame-by-frame basis, said coded image signal already coded on the frame-by-frame basis in the image coding apparatus;

switching between up-sampling on a field-by-field basis and a frame-by-frame basis according to mode information indicating whether coding was performed on the field-by-field basis or on the frame-by-frame basis.

27. An image decoding method, comprising:

decoding a coded image signal of a difference value between a detected pixel value change point and a predicted pixel value change point in a pixel block to obtain a decoded difference value, said coded image signal being coded on a field-by-field basis or on a frame-by-frame basis in an image coding apparatus, said pixel block already obtained by dividing a binary digital image;

predicting a next pixel value change point based on a decoded pixel value change position previously in the pixel block;

adding the decoded difference value to the predicted next pixel value change point;

restoring a field image from the addition result output on the field-by-field basis;

restoring a frame image from the addition result output on the frame-by-frame basis; and

switching between restoring on a field-by-field basis and a frame-by-frame basis according to mode information indicating whether the coding was performed on the field-by-field basis or on the frame-by-frame basis in the image coding apparatus.

28. An image decoding method, comprising:

determining a probability distribution of a pixel value of a target pixel based on a distribution of pixel values peripheral to the target pixel;

decoding an arithmetic-coded image signal from the probability distribution of the target pixel to generate a decoded image;

surveying a pixel value distribution of pixels peripheral to the target pixel on a field-by-field basis from the decoded image previously decoded and outputting the pixel value distribution as the survey result;

surveying the pixel value distribution of pixels peripheral to the target pixel on a frame-by-frame basis from the decoded image previously decoded and outputting the pixel value distribution as the survey result; and

switching between surveying on a field-by-field basis and a frame-by-frame basis according to mode information indicating whether the coding is performed on the field-by-field basis or on the frame-by-frame basis.

29. An image decoding method, comprising:

determining a probability distribution of a pixel value of a target pixel based on a distribution of pixel values peripheral to the target pixel;

decoding an arithmetic-coded image signal from the probability distribution of the target pixel to generate a decoded image;

performing motion compensation on a field-by-field basis on a pixel block to be decoded in the decoded image to generate a field prediction image, and surveying a pixel value distribution status of already decoded pixels peripheral to the target pixel in the field prediction image;

performing motion compensation on a frame-by-frame basis on the pixel block to be decoded in the decoded image to generate a frame prediction image, and surveying the pixel value distribution status of already decoded pixels peripheral to the target pixel in the frame prediction image; and

switching between performing and surveying on a field-by-field basis and a frame-by-frame basis according to mode information indicating whether the coding is performed on the field-by-field basis or on the frame-by-frame basis.

30. An image decoding method, comprising:

decoding a color digital image on a field-by-field basis, and decoding a binary digital image indicating a significant form of the color digital image on a field-by-field basis;

decoding said color digital image on a frame-by-frame basis, and decoding the binary digital image indicating the significant form of the color digital image on the frame-by-frame basis; and

switching between decoding on a field-by-field basis and a frame-by-frame basis according to mode information indicating whether coding for the color digital image is performed on the field-by-field basis or on the frame-by-frame basis.

31. An image decoding method, comprising:

decoding a color digital image on a field-by-field basis, and decoding a binary digital image indicating a significant form of the color digital image on a field-by-field basis;

decoding the color digital image on a frame-by-frame basis, and decoding a binary digital image indicating the significant form of the color digital image on the frame-by-frame basis; and

switching between decoding on a field-by-field basis and a frame-by-frame basis according to mode information indicating whether coding for the binary digital image is performed on the field-by-field basis or on the frame-by-frame basis.