1. Field of the Invention
The present invention relates to a digital image forming apparatus and particularly to a digital image forming apparatus capable of forming a color image in which an arbitrary color in a color original image is replaced by another arbitrary color different from the above mentioned arbitrary color.
2. Description of the Related Art
Digital image forming apparatus for forming a color image on paper have been proposed. Such a conventional digital image forming apparatus comprises a CCD image sensor for obtaining a digital image signal (for each of three primary colors RGB) from a color original image. A predetermined processing signal (for shading correction, color masking processing, underlying color removing processing, dither processing etc.) is applied to the image signal read by the image sensor. A printer (such as a laser printer, an LED printer or a liquid crystal display shutter printer) is driven by using the processed signal, so that a color image is formed on paper.
The conventional digital image forming apparatus includes an apparatus having a function of forming a color image in which an arbitrary color in an original image is replaced by another arbitrary color different therefrom, namely, a color conversion function.
Such an apparatus having the color conversion function designates arbitrary colors (i.e., an arbitrary color in an original image and another arbitrary color different therefrom for the conversion) in the below described manner.
(a) An arbitrary color is designated by operation of key switches on an operation panel or the like of the apparatus, those key switches corresponding to predetermined colors (normally, eight colors of R (red), G (green), B (blue), Y (yellow), M (magenta), C (cyan), K (black) and W (white) with a 1:1 relation.
(b) Coordinates of a desired color (a color to be designated as the above mentioned arbitrary color) in a color original image are inputted by using an edition coordinate input device. After that, the color original document is placed on the platen of the image forming apparatus and the color of the above mentioned coordinates is read by a CCD image sensor of the image forming apparatus, whereby the desired color is designated.
According to the above mentioned method (a), the key switches and the colors have the 1:1 correspondence. Accordingly, the method (a) has a disadvantage that the number of colors to be designated is limited by the number of key switches which can be provided on the panel or the like. On the other hand, according to the method (b), operations such as coordinate input operation and preliminary scanning of the CCD image sensor are complicated. Further, an additional device such as the coordinate input device is required.