Image coding apparatus and method thereof and coded image decoding apparatus and method thereof

• US 7,154,420 B2
• Filed: 12/11/2003
• Issued: 12/26/2006
• Est. Priority Date: 12/16/2002
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Muraoka, Hideya, Deoka, Yoshihiko
• Primary Examiner(s): Williams, Howard L.
• Application Number:
  US10/503,957
• Publication Number:
  US 20060214819A1
• Time in Patent Office: 1,111 Days
• Field of Search: 341/63, 358/423.13, 382/166, 382/239, 382/245
• US Class Current: 341/63
• CPC Class Codes: H04N 1/4175 involving the encoding of tone transitions with respect to tone transitions in a reference line
• CPC Class Codes: H04N 1/419 in which encoding of the length of a succession of picture-elements of the same value along a scanning line is the only encoding step H04N1/4135 - H04N1/417 take precedence
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/593 involving spatial prediction techniques
• CPC Class Codes: H04N 19/93 Run-length coding

Abstract

In order to decrease a required memory capacity of a line memory and to efficiently compress an image by coding, even when character information is contained in a high-resolution image, each time the block of an image that is equally divided into M (M: an arbitrary integer greater than 1) blocks in the horizontal direction is updated, difference data between color code data at corresponding pixel positions in the horizontal line and the adjacent immediately-preceding horizontal line with respect to each horizontal line within the block is detected by a line memory and an exclusive-OR circuit. After a run has been detected from the difference data corresponding to the horizontal lines from the exclusive-OR circuit by a run end detecting circuit, when a coded word is run-length coded by a code creating and outputting circuit, a coded word corresponding to a first run is run-length coded in the state in which information of difference data of the run is contained in this coded word and coded words corresponding to runs other than the first run are run-length coded in the state in which transition type information, indicative of the type of transition of the difference data of the immediately-preceding run to the difference data of the run is contained in the coded words.

Claims

1. In an image coding apparatus for an image in which color code data of 2 bits corresponds to each pixel on an image, the image coding apparatus comprising:

color code difference detecting means for detecting difference data between color code data of opposing pixel positions in divided horizontal lines and adjacent immediately-preceding divided lines with respect to each divided horizontal line within blocks forming an image, each time the blocks of the image equally divided into M (M;

an arbitrary integer greater than

     1) blocks in the horizontal direction are updated; and

run-length coding means for run-length coding a coded word corresponding to a first run in a state in which said run contains difference information, except when said run is a special run, and coded words corresponding to runs other than said first run in a state in which said run contains transition type information indicating a type of transition of the difference data of an immediately-preceding run to the difference data of said run instead of difference information of said run, except when said run is a special run, each time difference data corresponding to a divided horizontal line from said color code difference detecting means is run-length coded at every run.

2. The image coding apparatus according to claim 1, wherein said run-length coding means run-length codes a special run in which a coded word corresponding to a run having a length of 1 is set to a shortest constant word length and in which all difference data on divided horizontal lines are continued from a predetermined pixel position to an end pixel position in the form of “

00” and

a run in which a special coded word corresponding to said special run is set to a constant word length that does not contain difference information and in which all difference data on the divided horizontal lines are continued from a predetermined pixel position to an end pixel position in the form other than “

00” and

are the same, while said run length coding means run-length codes runs other than said first run and said special run in a state in which transition type information is set to 1 bit when the difference data of the immediately-preceding run is changed into the difference data “

00”

of said run and said run-length coding means run-length codes runs in a state in which transition type information is set to 2 bits when the difference data of the immediately-preceding run is changed into other difference data than said difference data “

00”

.

3. An image coding method for an image in which color code data of 2 bits corresponds to each pixel on an image, the image coding method comprising:

a color code difference detecting step for detecting difference data between color code data of opposing pixel positions in divided horizontal lines and adjacent immediately-preceding divided lines with respect to each divided horizontal line within blocks forming an image each time the blocks of the image equally divided into M (M;

an arbitrary integer greater than

     1) blocks in the horizontal direction are updated; and

a run-length coding step for run-length coding a coded word corresponding to a first run in a state in which said run contains difference information, except when said run is a special run, and coded words corresponding to runs other than said first run in a state in which said run contains transition type information indicating a type of transition of difference data of an immediately-preceding run to the difference data of said run instead of difference information of said run, except when said run is a special run, each time difference data corresponding to a divided horizontal line from said color code difference detecting means is run-length coded at every run.

4. The image coding method according to claim 3, further comprising run-length coding a special run in which a coded word corresponding to a run having a length of 1 is set to a shortest constant word length and in which all difference data on divided horizontal lines are continued from a predetermined pixel position to an end pixel position in the form of “

00” and

a run in which a special coded word corresponding to said special run is set to a constant word length that does not contain difference information and in which all difference data on the divided horizontal lines are continued from a certain pixel position to an end pixel position in a form other than “

00” and

are the same, while said run length coding method run-length codes runs other than said first run and said special run in a state in which transition type information is set to 1 bit when the difference data of the immediately-preceding run is changed into the difference data “

00”

of said run and said run-length coding means run-length codes runs in a state in which transition type information is set to 2 bits when the difference data of the immediately-preceding run is changed into other difference data than said difference data “

00”

.

5. A coded image decoding apparatus for a coded image run-length coded in which color code data of 2 bits corresponds to each pixel on an image, and in which a color code difference detecting is performed for detecting difference data between color code data of opposing pixel positions in divided horizontal and adjacent immediately-preceding divided lines with respect to each divided horizontal line within blocks forming an image is detected each time blocks of the image equally divided into M (M:

an arbitrary integer greater than

     1) blocks in the horizontal direction are updated, and a coded word corresponding to a first run is run-length coded in a state in which said run contains difference information, except when said run is a special run, and coded words corresponding to runs other than said first run in a state in which said run contains transition type information indicating a type of the transition of difference data of an immediately-preceding run to the difference data of said run instead of difference information of said run, except when said run is a special run, each time difference data corresponding to a divided horizontal line from said color code difference detecting means is run length coded at every run, the coded image decoding apparatus comprising;

coded word extracting means for sequentially extracting a coded word from a coded word string corresponding to divided horizontal lines sequentially inputted from an external source; and

decoding means for decoding the coded word extracted by said coded word extracting means.

6. The coded image decoding apparatus according to claim 5, wherein said decoding means decodes information of difference data corresponding to said coded word based on transition type information contained in said coded word and information of difference data corresponding to an immediately-preceding coded word when coded words other than predetermined coded words corresponding to a first coded word of a divided horizontal line and a special run are decoded.

7. A coded image decoding method for a coded image run-length coded in which color code data of 2 bits corresponds to each pixel on an image, a color code difference detecting step detects difference data between color code data of opposing pixel positions in divided horizontal lines and adjacent immediately-preceding divided lines with respect to each divided horizontal line within blocks forming the image is detected each time blocks of the image equally divided into M (M:

an arbitrary integer greater than

     1) blocks in the horizontal direction are updated and a coded word corresponding to a first run is run-length coded in a state in which said run contains difference information, except when said run is a special run, and coded words corresponding to runs other than said first run in a state in which said run contains transition type information indicating a type of transition of the difference data of an immediately-preceding run to the difference data of said run instead of difference information of said run, except when said run is a special run, each time difference data corresponding to a divided horizontal line from said color code difference detecting means is run-length coded at every run, the coded image decoding method comprising;

a coded word extracting step for sequentially extracting a coded word from a coded word string corresponding to divided horizontal lines sequentially inputted from an external source; and

a decoding step for decoding the coded word extracted by said coded word extracting step.

8. The coded image decoding method according to claim 7, wherein said decoding step decodes information of a difference corresponding to said coded word based on transition type information contained in said coded word and information of difference data corresponding to an immediately-preceding coded word when coded words other than predetermined coded words corresponding to a first coded word of a divided horizontal line and a special run are decoded.