Color separation in color graphics printing with limited memory

A method of compressing bit-map color graphics data for high-speed color separation comprising the steps of:

• if the color graphics data includes composite black data, forming a K plane having the same dimensions as the color planes for storing true black data, each bit location in the K plane corresponding to a respective bit location in the color planes, and moving composite black data out of the color planes and into the K plane for possible printing using black ink;
• defining an array of blocks of color data, each block corresponding to a predetermined rectangular array of bit locations in all the color planes;
• for each block of color data, examining the corresponding bit locations in all the color planes to detect an indication of a color dot in any of said planes;
• if a color dot is detected within the block, designating the block as a color block;
• for each block of color data, defining a corresponding K-plane block of black data, each K-plane block data thus corresponding to a predetermined rectangular array of bit locations in the K plane;
• for each K-plane block, examining the corresponding bit locations in the K plane to detect an indication of a black dot;
• if a black dot is detected within the block, designating the K-plane block as a black block;
• and
• defining as a white block each block of image data that is not designated as a color block or a black block.

In a liquid ink color graphics printing system, a method of controlling bleed between colors dots and true black dots in a printed image, comprising:

• selecting a minimum spacing requirement between color dots and true black dots adequate to control bleed therebetween in a printed image;
• dividing a page of the graphics input data to form a series of bands, each band of input data comprising a predetermined number of rows of bits;
• loading a first band of the series into a local memory space as a current band;
• examining the current band to identify all black data;
• attempting to determine a correct ink for printing the identified black data so as to maintain the minimum spacing between true black dots and color dots;
• if the correct ink can be determined, printing the band;
• if the correct ink cannot be determined, processing the band designating all black objects for printing with true black ink and spooling the output data to disk;
• sequentially examining a number of subsequent bands sufficient to determine whether the spooled data is correct;
• if the spooled output data is correct, forwarding the data to the printer;
• and
• if the spooled output data is incorrect, re-imaging the corresponding band of input data.