Image processing apparatus and image processing method

1. An image processing apparatus comprising:

an input unit that inputs image data;

an attribute information forming unit that forms attribute information for every pixel of the image data input by the input unit;

a dividing unit that divides the image data input by the input unit into a plurality of blocks each having a preset size;

a histogram forming unit that forms a histogram of colors which appear in a target block among the plurality of blocks divided by the dividing unit and of the number of pixels of each color;

a first deciding unit that, in the case where an area of a region having a target color obtained by the histogram formed by the histogram forming unit is larger than a preset first threshold value, decides that the region having the target color is a significant region;

a second deciding unit that, in the case where the area of the region having the target color obtained by the histogram formed by the histogram forming unit is equal to or smaller than the first threshold value and in the case where the region having the target color is located at a boundary of the target block and the attribute information formed by the attribute information forming unit for the pixel at the boundary in the region having the target color indicates a character attribute, decides that the region having the target color is a significant region;

a substituting unit that, in the case where the region having the target color is not decided to be a significant region by either one of the first and second deciding units, substitutes a color of another region adjacent to the region having the target color within the target block for a color of the pixel in the region having the target color; and

an integrating unit that, in the case where the region having the target color is decided to be a significant region by any one of the first and second deciding units and in the case where a chrominance difference between the region having the target color and another region, which is decided to be a significant region in another block adjacent to the target block, is equal to or less than a preset second threshold value, integrates the color of the region having the target color and a color of the other region decided to be the significant region in the other block.

2. An apparatus according to claim 1 , wherein in the case where the chrominance difference is larger than the second threshold value, in the case where the region having the target color is located at the boundary of the target block and the attribute information formed by the attribute information forming unit for the pixel at the boundary of the other block in the other region indicates the preset attribute, and in the case where the chrominance difference between the region having the target color and the other region in the other block is equal to or less than a third threshold value different from the second threshold value, the integrating unit integrates the color of the region having the target color and the color of the other region decided to be the significant region in the other block.

3. An apparatus according to claim 2 , wherein the third threshold value is larger than the second threshold value.

4. An apparatus according to claim 1 , wherein the attribute information forming unit forms the attribute information of a target pixel based on whether or not a region near the target pixel includes a predetermined number or more of pixels determined to be edges.

5. An apparatus according to claim 1 , wherein the attribute information forming unit forms the attribute information based on whether or not a target pixel is included in a text region.

6. An image processing method comprising:

inputting image data;

forming attribute information for every pixel of the input image data;

dividing the input image data into a plurality of blocks each having a preset size;

forming a histogram of colors which appear in a target block among the plurality of divided blocks and of the number of pixels of each color;

in the case where an area of a region having a target color obtained by the formed histogram is larger than a preset first threshold value, deciding in a first deciding step that the region having the target color is a significant region;

in the case where the area of the region having the target color obtained by the formed histogram is equal to or smaller than the first threshold value and in the case where the region having the target color is located at a boundary of the target block and the formed attribute information for the pixel at the boundary in the region having the target color indicates a character attribute, deciding in a second deciding step that the region having the target color is a significant region;

in the case where the region having the target color is not decided to be a significant region in either one of the first deciding step and the second deciding step, substituting a color of another region adjacent to the region having the target color within the target block for a color of the pixel in the region having the target color; and

in the case where the region having the target color is decided to be the significant region in any one of the first deciding step and the second deciding step and in the case where a chrominance difference between the region having the target color and another region, which is decided to be a significant region in another block adjacent to the target block, is equal to or less than a preset second threshold value, integrating the color of the region having the target color and a color of the other region decided to be the significant region in the other block.

7. A non-transitory computer-readable storage medium which stores a computer program, wherein the computer program allows the computer to execute an image processing method comprising:

inputting image data;

forming attribute information for every pixel of the input image data;

dividing the input image data into a plurality of blocks each having a preset size;

forming a histogram of colors which appear in a target block among the plurality of divided blocks and of the number of pixels of each color;

in the case where an area of a region having a target color obtained by the formed histogram is larger than a preset first threshold value, deciding in a first deciding step that the region having the target color is a significant region;

in the case where the area of the region having the target color obtained by the formed histogram is equal to or smaller than the first threshold value and in the case where the region having the target color is located at a boundary of the target block and the formed attribute information for the pixel at the boundary in the region having the target color indicates a character attribute, deciding in a second deciding step that the region having the target color is a significant region;

in the case where the region of the target color is not decided to be a significant region by either one of the first deciding step and the second deciding step, substituting a color of another region adjacent to the region having the target color within the target block for a color of the pixel in the region having the target color; and

in the case where the region having the target color is decided to be the significant region in any one of the first deciding step and the second deciding step and in the case where a chrominance difference between the region having the target color and another region, which is decided to be a significant region in another block adjacent to the target block, is equal to or less than a preset second threshold value, integrating the color of region having the target color and a color of the other region decided to be the significant region in the other block.