Image processing apparatus for converting color data by referring to a reconstructed color conversion table and an image processing method for the same

An image processing method that converts image data expressed in a first color system into image data expressed in a second color system, said image processing method comprising:

• a first step of storing a color conversion table representing a mapping of second image data expressed in the second color system to multiple lattice points, at which first image data generated in a color space of the first color system and expressed in the first color system are registered, wherein the color conversion table is encoded and represents a mapping of encoded second image data to the multiple lattice points, where the encoded second image data are obtained by an encoding process, which enhances a variation in tone value of the second image data in a predetermined tone area in the first color system, while compressing the variation in tone value of the second image data in a residual tone area;
• a second step of making the color conversion table subjected to a decoding process, so as to generate an intermediate color conversion table, where the decoding process restores the variation in tone value enhanced or compressed by the encoding process;
• a third step of specifying second image data corresponding to multiple lattice points, which are set to include at least different lattice points from newly added lattice points as well as existing lattice points, which are both included in the intermediate color conversion table, based on the intermediate color conversion table and making the specified second image data subjected to the encoding process, so as to reconstruct a color conversion table that is used for actual color conversion from the intermediate color conversion table and generate a reconstructed color conversion table;
• a fourth step of referring to the reconstructed color conversion table to convert the image data expressed in the first color system into encoded image data, which has gone through the encoding process;
• and
• a fifth step of making the encoded image data subjected to the decoding process to cancel out the encoding process, thus specifying the image data expressed in the second color system.

A computer-readable storage medium having a program stored thereon, said program including computer-executable instructions for causing a computer to attain an image processing method that converts image data expressed in a first color system into image data expressed in a second color system, said program comprising computer-executable instructions causing the computer to execute the following:

• a first function of storing a color conversion table representing a mapping of second image data expressed in the second color system to multiple lattice points, at which first image data generated in a color space of the first color system and expressed in the first color system are registered, wherein the color conversion table is encoded and represents a mapping of encoded second image data to the multiple lattice points, where the encoded second image data are obtained by an encoding process, which enhances a variation in tone value of the second image data in a predetermined tone area in the first color system, while compressing the variation in tone value of the second image data in a residual tone area;
• a second function of making the color conversion table subjected to a decoding process, so as to generate an intermediate color conversion table, where the decoding process restores the variation in tone value enhanced or compressed by the encoding process;
• a third function of specifying second image data corresponding to multiple lattice points, which are set to include at least different lattice points from newly added lattice points as well as existing lattice points, which are both included in the intermediate color conversion table, based on the intermediate color conversion table and making the specified second image data subjected to the encoding process, so as to reconstruct a color conversion table that is used for actual color conversion from the intermediate color conversion table and generate a reconstructed color conversion table;
• a fourth function of referring to the reconstructed color conversion table to convert the image data expressed in the first color system into encoded image data, which has gone through the encoding process;
• and
• a fifth function of making the encoded image data subjected to the decoding process to cancel out the encoding process, thus specifying the image data expressed in the second color system.