1.  Field of the Invention
The invention relates to a digital image processing apparatus, and more specifically to an image processor for retouching color images and a method thereof. 
2.  Description of the Related Art
Nowadays, digitally processed color images are frequently used as display images and still pictures appeared in printed matter.  In this case, image data is frequently retouched so as to obtain vivid images.  In particular, news photos need retouch processing because they are often shot under unfavorable conditions.  In a conventional digital image processing apparatus, color space image data, such as RGB or CMY, is treated and each primary color in color space image data is specified numerically for retouch processing.  RGB color space image data is used in visually displaying images on a display screen and CMY color space image data is used in printing images. 
FIG.  1 shows an example of conventional color space image data for printing and FIG.  2 shows a method of correcting that image data.  As shown in FIG.  1, in the case of image data of a color photo, the color of each pixel is specified by pixel values of the respective colors of cyan (C), magenta (M), yellow (Y), and black (K).  When an original color photo is reddish or yellowish because of fogging, its color tone is corrected.  In this case, as shown in FIG.  2, a conversion curve is displayed for each of colors of C, M, Y, and K and then revised to correct the color of that photo.  Using image data thus converted, a fog-free color photo is produced. 
However, the correction processing of RGB or CMY(K)-based color space image data has a problem that users have difficulty conjecturing the results of corrections made by specifying a numerical value for each color.  That is, sophisticated image processing techniques and experience are needed, which makes it impossible for amateurs to make corrections easily.  For example, in the case of color-photo correction as shown in FIG.  2, it is required for users to revise each conversion curve while recognizing changes in other colors.  It is therefore difficult to provide suitable instructions to change the image data.  This is the same case with RGB color space image data processing in which each color is represented by pixel values of red (R), green (G), and blue (B).