Method and apparatus for compensating for DOT gain in stochastic printing

Abstract

A method for compensating for dot gain in printing with stochastic screens comprises obtaining continuous tone CMYK files and screening the files at a resolution that is lower than the resolution of an output device that will be used to print the files. The lower resolution stochastically screened files are then expanded to the resolution of the output device, thereby effectively increasing the size of the dots by creating a number of subdots for each dot in the lower resolution stochastically screened files. Subdots within the expanded stochastically screened files can then be selectively removed to compensate for dot gain. In addition, overlapping dots in the screened CMYK files are removed and additional stochastically screened files are created that print a dot of a color of the previously overlapping dots and at the location of the previously overlapping dots to prevent colors from running together when printing on certain media. Finally, the removal of subdots in the expanded CMYK files can be performed to correct the color of the images when the expanded stochastically screened file is printed.

1 . A method of compensating for dot gain in stochastic screen files to be printed on an output device having a predefined resolution comprising: 
 receiving continuous tone CMYK files at a resolution less than the resolution of the output device;    screening the continuous tone CMYK files to produce stochastic CMYK files at a resolution less than the resolution of the output device;    expanding the stochastic CMYK files to have a resolution that is equal to the resolution of the output device wherein the expansion causes each dot in the stochastic CMYK file to be represented at a number of subdots in the expanded stochastic CMYK file; and    selectively removing a number of the subdots in the expanded stochastic CMYK file to compensate for dot gain when the expanded stochastic CMYK files are printed.    
     
     
         2 . The method of  claim 1 , wherein the output device is a printer.  
     
     
         3 . The method of  claim 1 , wherein the output device is an image setter or plate setter that produces films or plates of the expanded stochastic CMYK files.  
     
     
         4 . The method of  claim 1 , wherein the CMYK files are screened as a number of diamond shaped dots that are surrounded by grooves at 45°, wherein the diamond shaped dots and the grooves are expanded prior to the removal of selected subdots.  
     
     
         5 . A method of preventing color overlap in stochastic screen printing, comprising: 
 receiving continuous tone CMYK files;    screening the continuous tone CMYK files to produce stochastic CMYK screen files at a resolution less than the resolution of an output device;    determining if there are overlapping dots in the stochastic CMYK screen files and if so, removing the overlapping dots and adding one or more additional stochastic screen files having dots at the position of the overlapping dotes; and    printing colors with the additional stochastic screen file that represent the color of overlapping dots.    
     
     
         6 . The method of  claim 4 , wherein the stochastic screen files are expanded to create a number of subdots for each dot in the stochastic screen files and selectively removing subdots in the expanded stochastic screen file to compensate for dot gain.  
     
     
         7 . The method of  claim 6 , wherein the subdots are removed from a row and column of a cluster of subdots that correspond to a single dot in the lower resolution stochastic screen file to prevent colors from running together.  
     
     
         8 . A method of correcting color in printing the utilizes stochastic screens comprising: 
 receiving continuous tone CMYK files at a resolution less than a resolution of an output device;    screening the continuous tone CMYK files to produce stochastic CMYK files;    expanding the stochastic CMYK files to have a resolution of the output device, wherein the expansion causes each dot in the lower resolution stochastic screen file to be represented as a number of subdots in the expanded stochastic CMYK file; and    selectively removing-subdots from the expanded stochastic CMYK file to correct the color when the expanded stochastic CMYK files are printed.