To maintain or recover image information included in an original image data, and to restore it as image data when executing image processing for image data.

When JPEG data is opened in a personal computer 10, YCbCr-RGB conversion is executed. The converted RGB data may be included with negative color values outside of the range of color values in the sRGB color space 0-255 that is generally used in the personal computer 10 or color values greater than 255. The negative color values and color values greater than 255 of the RGB data are linearly compressed into the color value range of 0 to 255, and then linearly interpolated after image processing, so that degradation of RGB data after an original RGB data is image-processed, is reduced.

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