Image processing apparatus, image processing method, and computer-readable medium

An image processing method executed by an image processing apparatus, the method comprising:

• a tile division step of dividing image data, in which a pixel value of each pixel includes color data and attribute data, into tiles each including a predetermined number of pixels;
• a block division step of dividing each of the tiles, that are divided in the tile division step, into blocks each having a size of 2×2 pixels;
• a specification step of sequentially determining, as a processing object, each of the blocks divided in the block division step, and comparing pixel values of respective pixels in the block that is the processing object, thereby specifying a pattern flag indicating an arrangement pattern of pixel values included in each of the blocks;
• an extraction step of extracting first color data and first attribute data from a pixel value corresponding to a pixel at a predefined position in each of the blocks, and further extracting, from a block for which it is determined that the number of pixel values included in the block is one of 2 to 4, second color data to fourth color data and second attribute data to fourth attribute data corresponding to a second pixel value to a fourth pixel value corresponding to the arrangement pattern defined in the specified pattern flag;
• a first holding step of holding, in a memory, the pattern flag of each of the blocks, that is specified in the specification step, the first color data extracted in the extraction step, the second color data to fourth color data extracted in the extraction step, the first attribute data extracted in the extraction step, and the second attribute data to fourth attribute data extracted in the extraction step;
• a first determination step of determining whether attribute data of all pixels included in the tile are identical;
• if it is determined in the first determination step that the attribute data of all the pixels included in the tile are identical, a deletion step of controlling to delete the first attribute data and the second attribute data to fourth attribute data, that are held in the first holding step, and store, in header information, information indicating that the attribute data in the tile are identical and information of the attribute data determined to be identical;
• and
• wherein at least one of the steps is performed by a processor.