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

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.

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.

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.