Image processing apparatus and image processing method

1. A non-transitory computer program product having a computer readable medium including programmed instructions for image processing, wherein the instructions, when executed by a computer, cause the computer to perform:

sectioning an image to be processed into a plurality of blocks;

rearranging the blocks into positions specified by an encryption key that uniquely specifies the positions of the blocks in the image;

setting a minimum area which is a part of the block and smaller than the block, with respect to each of the blocks rearranged at the rearranging;

determining a computing method used to convert pixel values of pixels that form the minimum area set at the setting based on statistical characteristics computed from predetermined pixels forming an area near the minimum area and not belonging to the minimum area; and

converting the pixel values of pixels that form the minimum area based on the computing method determined at the determining without converting pixel values of pixels including the predetermined pixels other than the pixels forming the minimum area in each of the blocks.

2. The non-transitory computer program product according to claim 1 , wherein the converting includes using a computing method that reversibly converts the pixel values.

3. The non-transitory computer program product according to claim 1 , wherein the converting includes using a computing method that non-reversibly converts the pixel values.

4. The non-transitory computer program product according to claim 1 , wherein

each of the pixels is represented by one or more color components indicative of a color having a value, and

the converting includes converting a part or all of the color components included in each of the pixels that form the minimum area.

5. The non-transitory computer program product according to claim 1 , wherein

each of the pixels is represented by a brightness component indicative of a degree of brightness and a color-difference component indicative of a difference between the brightness component and a color component indicative of a color, both the brightness component and the color-difference component having a value, and

the converting includes converting the pixel values of one or both of the brightness component and the color-difference component included in each of the pixels that form the minimum area.

6. The non-transitory computer program product according to claim 1 , further causing the computer to perform:

issuing a first warning when the image to be processed cannot be sectioned into a predetermined number of the blocks with a predetermined size during the sectioning, and

issuing a second warning when there are more than a predetermined number of the blocks that include pixels having same pixel values.

7. The non-transitory computer program product according to claim 1 , wherein,

the converting includes, when the image is a binary image, converting the pixel values by using converting method, when the image is not a binary image, converting by the pixel values by using the computing method determined at the determining.

8. The non-transitory computer program product according to claim 1 , wherein the determining includes determining the computing method based on statistical characteristics computed from the predetermined pixels, the predetermined pixels being pixels of the block proximate to the minimum area.

9. A computer program product having a non-transitory computer readable medium including programmed instructions for image processing, wherein the instructions, when executed by a computer, cause the computer to perform:

in a converted image generated by sectioning an image into a plurality of blocks, rearranging the blocks, setting a minimum area which is a part of the block and smaller than the block, with respect to each of the rearranged blocks, determining a computing method used to convert pixel values of pixels that form the minimum area set at the setting based on statistical characteristics computed from predetermined pixels forming an area near the minimum area and not belonging to the minimum area, and converting the pixel values of pixels that form the minimum area based on the computing method without converting pixel values of pixels including the predetermined pixels other than the pixels forming the minimum area in each of the rearranged blocks, detecting a position of the minimum area having a converted pixel value by using a filter;

determining a computing method used to restore the converted pixel value to an original pixel value before the pixel value was converted by the computing method by identifying the computing method for the minimum area;

restoring the pixel values of the pixels that form the minimum area; and

reverse-rearranging the blocks in original positions thereof in the image before the blocks were rearranged by using an encryption key.

10. The computer program product according to claim 9 , further causing the computer to execute compensating the pixel values of the pixels that form the minimum area having the converted pixel value detected at the detecting using a pixel value computed based on statistical characteristics of the predetermined pixels.

11. The computer program product according to claim 9 , wherein

the converted image is an image obtained by scanning a printed image.

12. An image processing unit comprising:

a processor coupled to a memory,

wherein the processor is programmed to execute:

sectioning an image to be processed into a plurality of blocks;

rearranging the blocks into positions specified by an encryption key that uniquely specifies the positions of the blocks in the image;

setting a minimum area which is a part of the block and smaller than the block, with respect to each of the blocks rearranged at the rearranging;

determining a computing method used to convert pixel values of pixels that form the minimum area set at the setting based on statistical characteristics computed from predetermined pixels forming an area near the minimum area and not belonging to the minimum area; and

converting the pixel values of pixels that form the minimum area based on the computing method determined at the determining without converting pixel values of pixels including the predetermined pixels other than the pixels forming the minimum area in each of the blocks.

13. An image processing method comprising:

sectioning an image to be processed into a plurality of blocks;

rearranging the blocks into positions specified by an encryption key that uniquely specifies the positions of the blocks in the image;

setting, using a processor, a minimum area which is a part of the block and smaller than the block, with respect to each of the blocks rearranged at the rearranging;

determining a computing method used to convert pixel values of pixels that form the minimum area set at the setting based on statistical characteristics computed from predetermined pixels forming an area near the minimum area and not belonging to the minimum area; and

converting pixel values of pixels that form the minimum area based on the computing method determined at the determining without converting pixel values of pixels including the predetermined pixels other than the pixels forming the minimum area in each of the blocks.

14. An image processing system comprising a first image processing apparatus and a second image processing apparatus, wherein

the first image processing apparatus includes

a processor coupled to a memory,

wherein the processor is programmed to execute:

sectioning an image to be processed into a plurality of blocks;

rearranging the blocks into positions specified by an encryption key that uniquely specifies the positions of the blocks in the image;

setting a minimum area which is a part of the block and smaller than the block, with respect to each of the blocks rearranged at the rearranging;

determining a computing method used to convert pixel values of pixels that form the minimum area set at the setting based on statistical characteristics computed from predetermined pixels forming an area near the minimum area and not belonging to the minimum area; and

converting pixel values of pixels that form the minimum area based on the computing method determined at the determining without converting pixel values of pixels including the predetermined pixels other than the pixels forming the minimum area in each of the blocks, and

the second image processing apparatus includes

a detecting unit that, in the rearranged image, detects a position of a minimum area having a converted pixel value by using a filter, wherein a computing method used to convert the pixel values is determined based on predetermined pixels that do not belong to each of the minimum area;

a determining unit that determines a decryption computing method used to restore the converted pixel value to an original pixel value before the pixel value was converted by the computing method by identifying the computing method for the minimum area;

a restoring unit that restores the pixel values of the pixels that form the minimum area; and

a reverse-rearranging that reverse-rearranges the blocks in original positions thereof in the image before the blocks were rearranged by using an encryption key.