Image coding system, image decoding system, image processing system, image coding method, image decoding method, and image processing method

• US 6,343,157 B1
• Filed: 02/19/1999
• Issued: 01/29/2002
• Est. Priority Date: 03/05/1998
• Status: Expired due to Fees

• Current Assignee: Fuji Xerox Company Limited (Xerox Holdings Corp.)
• Original Assignee: Fuji Xerox Company Limited (Xerox Holdings Corp.)
• Inventors: Yada, Shinichi
• Primary Examiner(s): Grant, II, Jerome
• Application Number:
  US09/253,518
• Time in Patent Office: 1,075 Days
• Field of Search: 358/427, 358/426, 358/261.1, 382/244, 382/246
• US Class Current: 382/246
• CPC Class Codes: G06T 9/007 Transform coding, e.g. discrete cosine transform
• CPC Class Codes: H04N 1/41 Bandwidth or redundancy reduction by scanning H04N1/17 ; methods or arrangements for coding, decoding, compressing or decompressing digital video signals H04N19/00

Abstract

A raster/block conversion circuit 12 divides an input image from an image input unit 11 into blocks. An image characteristic determination circuit 13 calculates the image characteristic for each block, thereby determining the image type for each block. Based on the determination result of the image characteristic determination circuit 13, a switch circuit 18 adaptively switches an ADCT coding circuit 14 adopting a variable-length irreversible coding technique and an intrablock quad coding circuit 15, an intrablock binary coding circuit 16, and a block run length coding circuit 17 adopting a fixed-length irreversible coding technique.

Claims

1. An image coding system comprising:

block division means for dividing an input image into blocks each containing a plurality of pixels;

image characteristic determination means for determining a characteristic of an image in each of the blocks divided by said block division means;

variable-length coding means for performing variable-length coding for the input image;

fixed-length coding means for performing fixed-length coding for the input image; and

control means for selecting either of said variable-length coding means and said fixed-length coding means based on the determination result of said image characteristic determination means and controlling said selected coding means to execute coding for the input image.

2. The image coding system as claimed in claim 1, further comprising:

multiplexing means for adding to code data coded by said variable-length coding means or said fixed-length coding means, identification information of said variable-length coding means or said fixed-length coding means performing the coding and outputting the code data to which the identification information being added.

3. The image coding system as claimed in claim 1, wherein

if said image characteristic determination means determines that the image in the block is a natural drawing, said control means selects said variable-length coding means, and wherein

if said image characteristic determination means determines that the image in the block is a line drawing, said control means selects said fixed-length coding means.

4. The image coding system as claimed in claim 1, wherein

said control means comprises comparison means for comparing a data amount of the code data coded by said variable-length coding means with a predetermined threshold value, and wherein

if said comparison means determines that the data amount of the code data is smaller than the threshold value, said variable-length coding means is selected, and

if said comparison means determines that the data amount of the code data is greater than the threshold value, said fixed-length coding means is selected.

5. The image coding system as claimed in claim 4, wherein

the predetermined threshold value is a maximum code amount for each block set from a preset target minimum coding ratio of an image.

6. The image coding system as claimed in claim 1, wherein

said variable-length coding means and said fixed-length coding means perform irreversible coding for the input image.

7. The image coding system as claimed in claim 6, wherein

said variable-length coding means performs orthogonal transformation coding.

8. The image coding system as claimed in claim 6, wherein

the fixed-length irreversible coding performed by said fixed-length coding means is block truncation coding.

9. The image coding system as claimed in claim 8, wherein

said fixed-length coding means comprises a plurality of block truncation coding means.

10. The image coding system as claimed in claim 9, wherein

said control means selects one of the block truncation coding means based on the determination result of said image characteristic determination means.

11. The image coding system as claimed in claim 1, wherein

an image in each block determined by said image characteristic determination means has the characteristic of containing at least the number of different pixel values of the image in the block.

12. The image coding system as claimed in claim 11, wherein

if it is determined that the number of different pixel values determined by said image characteristic determination means is equal to or less than a predetermined threshold value, said control means selects said fixed-length coding means.

13. The image coding system as claimed in claim 11, wherein

said control means selects one of said block truncation coding means based on the number of different pixel values determined by said image characteristic determination means.

14. The image coding system as claimed in claim 13, wherein

said control means selects block truncation coding means having as many representative values as the number of different pixel values determined by said image characteristic determination means from among said block truncation coding means.

15. The image coding system as claimed in claim 1, wherein

an image in each block determined by said image characteristic determination means has the characteristic of containing at least an occurrence frequency distribution of pixel values of the image in the block.

16. The image coding system as claimed in claim 15, wherein

if said image characteristic determination means determines that pixels of a predetermined value or more are distributed in the proximity of an end of the occurrence frequency distribution of the pixel values of the image in the block, said control means selects said fixed-length coding means.

17. An image decoding system for decoding code data coded using variable-length coding or fixed-length coding for an input image divided into blocks based on the determination result of determining an image characteristic for each block, the code data to which identification information indicating the used coding type is added,

said image decoding system comprising:

extraction means for extracting the identification information from the code data;

variable-length decoding means for performing variable-length decoding of the code data from which the identification information is extracted;

fixed-length decoding means for performing fixed-length decoding of the code data from which the identification information is extracted; and

control means for selecting either of said variable-length decoding means and said fixed-length decoding means based on the identification information extracted by said extraction means and controlling said selected decoding means to execute decoding for the code data from which the identification information is extracted.

18. An image processing system comprising:

an image coding system for dividing an input image into blocks each containing a plurality of pixels, determining an image characteristic for each block, executing coding for the input image using variable-length coding or fixed-length coding based on the determination result, and outputting code data to which identification information indicating the used coding type is added; and

an image decoding system for extracting the identification information from the code data output from said image coding system, decoding the code data from which the identification information is extracted using variable-length decoding or fixed-length decoding corresponding to the extracted identification information, and outputting the decoded data.

19. An image coding method comprising the steps of:

dividing an input image into blocks each containing a plurality of pixels;

determining a characteristic of an image in each block;

selecting either of variable-length coding and fixed-length coding based on the determination result; and

executing the selected coding for the input image.

20. The image coding method as claimed in claim 19, wherein

identification information indicating the used coding type of variable-length coding or fixed-length coding is added to the code data coded using either of the variable-length coding and the fixed-length coding and the code data to which the identification information is added is output.

21. An image decoding method for decoding code data coded

using variable-length coding or fixed-length coding for an input image divided into blocks based on the determination result of determining an image characteristic for each block, the code data to which identification information indicating the used coding type is added,

said image decoding method comprising the steps of:

extracting the identification information from the code data;

selecting either of the variable-length decoding and the fixed-length decoding based on the extracted identification information; and

executing decoding for the code data from which the identification information is extracted.

22. An image processing method comprising the steps of:

dividing an input image into blocks each containing a plurality of pixels;

determining a characteristic of an image in each block;

selecting either of variable-length coding and fixed-length coding based on the determination result;

executing the selected coding for the input image;

adding identification information indicating the selected coding type of variable-length coding or fixed-length coding;

outputting the code data to which the identification information is added;

extracting the identification information from the code data;

selecting either of the variable-length decoding and the fixed-length decoding based on the extracted identification information; and

executing decoding for the code data from which the identification information is extracted.

23. A printing system comprising:

block division means for dividing an input image into blocks each containing a plurality of pixels;

image characteristic determination means for determining a characteristic of an image in each of the blocks provided by said block division means;

variable-length coding means for performing variable-length coding for the input image;

fixed-length coding means for performing fixed-length coding for the input image;

control means for selecting either of said variable-length coding means and said fixed-length coding means based on the determination result of said image characteristic determination means and controlling said selected coding means to execute coding for the input image; and

storing memory for storing less than the fixed-length coding.