JP2003174562A5 - - Google Patents

Claims (20)

Generating means for performing pseudo halftone processing on the first image to generate a second image;
Compression means for performing compression processing for each area constituting the second image,
Further, the compression means includes:
For each of the regions, using the target pixel and a reference pixel having a predetermined positional relationship with the target pixel, it is determined whether or not the value of the target pixel and the reference pixel are substantially the same. As a result, when the values are substantially the same, the information indicating that the value of the target pixel is the same as the value of the reference pixel and the information indicating the predetermined positional relationship are not substantially the same. Wherein the compressed data for each area is generated by sequentially recording the compressed data. 2. The image compression apparatus according to claim 1, wherein the first image is a color still image, and the second image has a smaller number of bits constituting one pixel than the first image. . 3. The image compression apparatus according to claim 1, wherein the generation unit generates the second image by performing pseudo halftone processing on the first image using a dither pattern. 4. . 4. The apparatus according to claim 1, wherein the compression unit further includes a division unit configured to divide the second image into blocks each having a predetermined size, and compresses each of the areas in units of divided blocks. 5. An image compression device as described in the above. The compression means further comprises:
A storage unit that stores information indicating a positional relationship between the plurality of reference pixel candidates serving as the reference pixel candidates and the target pixel,
Using each reference pixel candidate specified by each piece of the information stored in the storage unit and the target pixel, a size of compressed data for each reference pixel candidate is obtained, and the size is determined by a predetermined condition. A positional relationship specifying unit that specifies a positional relationship between the reference pixel candidate and the target pixel when the condition is satisfied,
A pixel having a positional relationship specified by the positional relationship specifying unit with the target pixel is set as the reference pixel, and compression is performed for each region using the reference pixel and the target pixel. The image compression device according to any one of claims 1 to 4. The information stored in the storage unit and indicating the positional relationship between the plurality of reference pixel candidates serving as the reference pixel candidates and the target pixel is based on the type of the pseudo halftone processing and the area. The image compression apparatus according to claim 5, wherein The information indicating the positional relationship between the plurality of reference pixel candidates serving as the reference pixel candidates and the target pixel stored by the storage unit is information indicating a relative position of each reference pixel candidate with respect to the position of the target pixel. The image compression device according to claim 5, wherein: The image compression apparatus according to claim 7, wherein the relative position indicates the number of lines immediately above the position of the target pixel and a shift amount in a line direction. The image compression apparatus according to claim 7, wherein the relative position indicates the number of lines immediately above the position of the target pixel. The positional relationship specifying unit obtains the size of compressed data for each of the reference pixel candidates using each of the reference pixel candidates and the target pixel specified by each of the pieces of information stored in the storage unit, The image compression apparatus according to claim 5, wherein a positional relationship between a reference pixel candidate that minimizes the size and the pixel of interest is specified. The positional relationship specifying unit obtains the size of compressed data for each of the reference pixel candidates using each of the reference pixel candidates and the target pixel specified by each of the pieces of information stored in the storage unit, The image compression apparatus according to claim 5, wherein a positional relationship between a reference pixel candidate whose size is equal to or smaller than a predetermined size and the target pixel is specified. The image compression apparatus according to claim 1, wherein the area is a color plane. First information indicating whether or not the value of the target pixel is the same as the value of the reference pixel, which is included in the compressed data that has been subjected to the pseudo halftone process and compressed for each region; Storage means for storing second information indicating the positional relationship of
If the first information is determined to be information indicating that the value of the target pixel is the same as the value of the reference pixel, a reference pixel for the target pixel is specified by referring to the second information; Updating the first information to a value of the specified reference pixel,
When it is determined that the first information is information indicating that the value of the pixel of interest is not the same as the value of the reference pixel, a decompression unit that sets the first information to the value of the pixel of interest is provided. Characteristic image decompression device. Performing a pseudo halftone process on the first image to generate a second image;
A compression step of performing a compression process for each area constituting the second image,
Further, the compression step includes:
For each of the regions, using the target pixel and a reference pixel having a predetermined positional relationship with the target pixel, it is determined whether or not the value of the target pixel and the reference pixel are substantially the same. As a result, when the values are substantially the same, the information indicating that the value of the target pixel is the same as the value of the reference pixel and the information indicating the predetermined positional relationship are not substantially the same. Wherein the compressed data is sequentially recorded to generate compressed data for each area. 15. The method according to claim 14, wherein the compression step further includes a division step of dividing the second image into blocks each having a predetermined size, and performing compression for each of the regions in units of the divided blocks. Image compression method. The compression step further comprises:
A storage step of storing information indicating a positional relationship between the plurality of reference pixel candidates serving as the reference pixel candidates and the target pixel in a predetermined storage unit,
Using each reference pixel candidate specified by each piece of the information stored in the storage unit and the pixel of interest, the size of compressed data for each reference pixel candidate is obtained, and the size is determined by a predetermined condition. A positional relationship specifying step of specifying a positional relationship between the reference pixel candidate and the pixel of interest when satisfied.
A pixel having a positional relationship specified in the positional relationship specifying step with the target pixel is set as the reference pixel, and compression is performed for each region using the reference pixel and the target pixel. 16. The image compression method according to 14 or 15. First information indicating whether or not the value of the target pixel is the same as the value of the reference pixel, which is included in the compressed data that has been subjected to the pseudo halftone process and compressed for each region; Storing the second information indicating the positional relationship of the information in a predetermined storage means;
If the first information is determined to be information indicating that the value of the target pixel is the same as the value of the reference pixel, a reference pixel for the target pixel is specified by referring to the second information; Updating the first information to a value of the specified reference pixel,
When determining that the first information is information indicating that the value of the pixel of interest is not the same as the value of the reference pixel, an expansion step of setting the first information to the value of the pixel of interest. Characteristic image decompression method. A program for causing a computer to execute the image compression method according to any one of claims 14 to 16. A program for causing a computer to execute the image decompression method according to claim 17. A computer-readable storage medium storing the program according to claim 18.