JP2008104121A5

JP2008104121A5 -

Info

Publication number: JP2008104121A5
Application number: JP2006286885A
Authority: JP
Filing date: 2006-10-20
Publication date: 2009-11-19
Anticipated expiration: 2026-10-20

Claims

Image data character line image and tone image are mixed in an image encoding device for encoding,
Input means for inputting image data to be encoded in units of blocks composed of a plurality of pixels;
Extracting entered the block of interest or, et al., The character line image pixel data, the identification information for each pixel in the block of interest to identify whether the pixel data of one gradation attribute is a pixel data of a character line image Extraction means;
A first encoding means for encoding the pixel data of the character line image extracted by the extraction means,
Second encoding means for encoding the identification information extracted by the extraction means;
The included in the target block, for each sub-block which is a unit for performing orthogonal transformation, substitution pixel data extracted as a character line image in the sub-block is determined based on the pixel data having gradation attributes A replacement means for replacing with a value;
Third encoding means for orthogonally transforming and encoding the image data of each sub-block after being replaced by the replacement means;
Code string generation means for combining the encoded data generated by the first to third encoding means and generating encoded data of the block of interest ;
The replacement means includes
DC component calculation means for calculating a DC component when it is assumed that the target sub- block in the target block is composed only of pixels having a gradation attribute;
Replacement candidate values determined based on the DC component value of the immediately preceding sub-block of the target sub block, determines whether it is in the range of values of a pixel group having a gradation attributes of said target sub-block Judgment means,
When the determination means determines that the replacement candidate value is within the range, a value that approximates the DC component value of the immediately preceding subblock is determined as the replacement value of the target subblock ;
In the determination unit, when the replacement candidate value is determined to be outside the range, a value approximating the DC component value of the target sub-block when the target sub-block is assumed to have only the pixels of the tone attributes An image encoding apparatus comprising: a determining unit that sets the replacement value.

It said first, second encoding means is a lossless coding means, the third coding means is a lossy JPEG encoding means,
The target sub-block is composed of 8 × 8 pixels, and the number of pixels having the attribute of a character line drawing of which N, the sum of the pixel data having gradation attribute, and the average value D, and Dave, 1 If a pixel is represented by 8 bits ,
The direct current component calculation means obtains a direct current component DC calculated at the time of DCT conversion by the following equation:
DC = (D + Dave × N−128 × 64) / 8
Said determining means determines the DC component of the immediately preceding sub-block DC _-1, when the DC component of the target sub block and the DC _0, in accordance with any of the following equation which is the substitution value of the target sub block Z Z = (8 × D C ₋₁ −D + 128 × 64) / N
Or
Z = (8 × D C ₀ −D + 128 × 64) / N
The image coding apparatus according to claim 1.

Further, the replacement means determines the remainder value R generated when determining the replacement value Z according to the following equation:
R = (8 × D C ₋₁ −D + 128 × 64)% N
Or
R = (8 × D C ₀ −D + 128 × 64)% N
(A% B is a function that returns the remainder when integer A is divided by integer B)
The data of “N−R” pixels determined as the character / line image is replaced with a replacement value Z,
The image coding apparatus according to claim 2, wherein data of R pixels determined as the character / line image is replaced with "Z + 1".

If the target sub-block is the head of the sub-blocks of a block, the determination unit, the target sub-block is the replacement value a value that approximates the DC component value when assumed to have only the pixels of the tone attributes The image encoding apparatus according to claim 1, wherein:

Image data character line image and tone image are mixed method of controlling an image encoding device for encoding,
An input process for inputting image data to be encoded in units of blocks each composed of a plurality of pixels;
Extracting entered the block of interest or, et al., The character line image pixel data, the identification information for each pixel in the block of interest to identify whether the pixel data of one gradation attribute is a pixel data of a character line image An extraction process;
A first encoding step of encoding the pixel data of the character line image extracted in the extraction step,
A second encoding step for encoding the identification information extracted in the extraction step;
The included in the target block, for each sub-block which is a unit for performing orthogonal transformation, substitution pixel data extracted as a character line image in the sub-block is determined based on the pixel data having gradation attributes A replacement step of replacing with a value;
A third encoding step of orthogonally transforming and encoding the image data of each sub-block after being replaced in the replacement step;
A code string generation step of combining the encoded data generated in the first to third encoding steps and generating encoded data of the block of interest ,
The replacement step includes
A direct current component calculation step for calculating a direct current component when it is assumed that the target sub- block in the target block includes only pixels having a gradation attribute;
Substituted candidate values determined based on the DC component value of the immediately preceding sub-block of the target sub block, determines whether it is in the range of values of a pixel group having a gradation attributes of said target sub-block A decision process;
In the determination step, when it is determined that the replacement candidate value is within the range, a value that approximates the DC component value of the immediately preceding sub-block is determined as the replacement value of the target sub-block ,
In the determination step, when the replacement candidate value is determined to be outside the range, a value approximating the DC component value of the target sub-block when the target sub-block is assumed to have only the pixels of the tone attributes And a determining step for setting the replacement value. A method for controlling an image encoding device.

By computer executes reading, computer program characterized the computer function as an image encoding apparatus according to any one of claims 1 to 4.

A computer-readable storage medium storing the computer program according to claim 6.