Color image forming apparatus

A color image forming apparatus comprising:

• a first image processing unit and a second image processing unit, each having:
• a photosensitive body,
• an exposing device for forming an electrostatic latent image by exposing a surface of said photosensitive body, and
• a plurality of developing devices each supplying said electrostatic latent image with toner of a different color provided that one of said plurality of developing devices in said first image processing unit withholds black toner,
• a color image being formed by transferring toner images formed on said photosensitive bodies in said first and second image processing units so as to be superimposed over one another,
• an additional information composite section for producing a composite image by combining a chief monochrome image with additional information, said additional information forming an image different from said chief monochrome image, and
• a central processing unit for having said first image processing unit form said chief monochrome image and said second image processing unit form the image of said additional information,
• said chief monochrome image and said image of said additional information being formed simultaneously when said chief monochrome image is to be combined with said image of said additional information in a color other than black to produce a composite image.

A color image forming apparatus comprising:

• first and a second image processing units for forming toner images of different colors, respectively;
• a layering section for layering said toner images formed by said first and second image processing units;
• image data lines respectively serving as first and second systems, said first and second systems selectively sending image data of respective corresponding colors based on an original image to said first and second image processing units;
• and
• an additional information memory, connected to said image data line serving as said second system, for storing additional image data which forms an image different from said original image and will be combined with said image data sent to said image line serving as said second system to produce a composite image,
• said second image processing unit being another image processing unit than said first image processing unit whose one of said plurality of developing devices withholds black toner, and forms said image of said additional image data, and
• said original image and said image of said additional image data being formed simultaneously when said original image is a monochrome image and is to be combined with said image of said additional image data in a color other than black to produce a composite image.