Conversion correcting method of color image data and photographic processing apparatus implementing the method

An image processing apparatus for correcting pixel values of each pixel constituting color image data by shifting, in a coordinate system, a mathematical correction function defining correction values for respective input values, the apparatus comprising a color balance adjustment section for adjusting color balance of the corrected image data, the color balance adjustment section comprising:

• a calculating section for determining a maximum value and a minimum value among correction values (b, g, r) of respective color components obtained for each pixel by using said correction function, calculating difference (Δb, Δg, Δr) between the respective correction values of the respective color components and said minimum value, calculating a difference (DR) between said maximum value and said minimum value, and dividing said calculated differences (Δb, Δg, Δr) between the correction values of the respective color components and said minimum value by said calculated difference (DR) between said maximum value and said minimum value, thereby to obtain color ratios (Cb, Cg, Cr) for the respective color components;
• a judging section for determining as an inappropriate pixel, any pixel having a correction value overflowing from a predetermined maximum output gradation value and setting said overflowing correction value to said predetermined maximum output gradation value, and determining as an inappropriate pixel, any pixel having a correction value underflowing from a predetermined minimum output gradation value and setting said underflowing correction value to said predetermined minimum output gradation value;
• and
• a gradation value determining section for controlling color balance adjustment so as to cause the correction values of said inappropriate pixel to agree with said respective color ratio thereof.

A computer-readable medium having stored thereon computer executable instructions, which when executed performs the steps of:

• determining a maximum value and a minimum value among correction values (b, g, r) of respective color components obtained for each pixel by using said correction function, calculating differences (Δb, Δg, Δr) between the respective correction values of the respective color components and said minimum value, and calculating a difference (DR) between said maximum value and said minimum value;
• dividing said calculated differences (Δb, Δg, Δ) between the respective correction values of the respective color components and said minimum value by said calculated difference (DR) between said maximum value and said minimum value, thereby to obtain color ratios (Cb, Cg, Cr) for the respective color components;
• determining, as an inappropriate pixel, any pixel having a correction value overflowing from a predetermined maximum output gradation value and setting said overflowing correction value to said predetermined maximum output gradation value, and determining, as an inappropriate pixel, any pixel having a correction value underflowing from a predetermined minimum output gradation value and setting said underflowing correction value to said predetermined minimum output gradation value;
• and
• controlling color balance adjustment so as to cause the correction values of said inappropriate pixel to agree with said respective color ratio thereof.

An image processing apparatus for outputting image data consisting of a plurality of image data described in the RGB color system in a predetermined gradation range, the apparatus comprising:

• a conversion section for converting the image data in the RGB color system into a different color system for image quality adjustment to provide converted image data;
• an image quality adjustment section for adjusting image quality of the converted image, data;
• a reverse conversion section for reverse converting the image quality adjusted image data back into the ROB color system to provide a reverse-converted image data;
• a judging section for determining whether pixel values of each pixel constituting the reverse-converted image data are confined within said predetermined gradation range;
• and
• a color balance adjustment section for performing a predetermined calculation on pixel values of the respective color components included in each pixel determined as being out of said predetermined gradation range by the judging section, thereby to cause the pixel values thereof to be confined within said predetermined gradation range, and adjusting said pixel values of said each pixel to fixedly maintain a ratio among the pixel values of the respective color components based on the minimum value among said pixel values.