System and method for analyzing print quality

Abstract

A method is provided for analyzing the colour quality of a press pull as compared to a contract proof. The contract proof is scanned to create image data including colour data representing a scanned proof image. The press pull is also scanned to create image data including colour data representing a scanned press pull image. The scanned images are simultaneously displayed on a video monitor, and, the displayed images are searched for any significant differences in colour. A method is also provided for printing colour products on a colour printing press in a print run associated with a contract proof. The contract proof is scanned to create image data including colour data representing a scanned proof image. A sample printed colour product from the press is also scanned to create image data including colour data representing a scanned press pull image. The scanned images are simultaneously displayed on a video monitor. The scanned images are aligned and linked. The colour data for each section of one image is automatically compared with the colour data for a linked corresponding section of the other image to determine whether any differences exceed a pre-determined threshold. A count indicative of the number of sections which are determined to exceed such threshold is maintained. It is determined whether the number of sections which exceed such threshold exceeds a pre-determined overall threshold to determine colour quality. If the overall threshold is not exceeded, the print run is continued. If the overall threshold is exceeded, the print run is temporarily stopped, the print variables are adjusted and the print run is resumed. The preceding steps are repeated from the remove sample step until the print run is complete. A system is provided for analyzing the colour quality of a press pull as compared to a contract proof comprising at least one scanner for scanning the contract proof and for scanning the press pull, an image comparator connected to the at least one scanner to receive the data for the scanned proof image and the scanned press pull image and a video monitor connected to the image comparator to receive the data for the scanned proof image and the scanned press pull image and to display the scanned images simultaneously.

1 . A method for analyzing the colour quality of a press pull as compared to a contract proof comprising:
 scanning the contract proof to create image data including colour data representing a scanned proof image,   scanning the press pull to create image data including colour data representing a scanned press pull image,   displaying the scanned images simultaneously on a video monitor, and,   searching the displayed images for any significant differences in colour.   
     
     
         2 . The method of  claim 1  wherein the scans are performed in a manner to render them in colour calibration with each other. 
     
     
         3 . The method of  claim 2  wherein the scans are performed simultaneously on a scanner. 
     
     
         4 . The method of  claim 2  wherein the scans are performed sequentially on a single scanner within a time period in which colour calibration of the scanner will not drift significantly. 
     
     
         5 . The method of  claim 1  further comprising the steps of:
 selecting corresponding portions of the scanned images,   calculating an average for the colour data associated with said selected portions,   calculating the difference between the averages, and,   comparing the difference to a pre-determined threshold to determine colour quality.   
     
     
         6 . The method of  claim 1  wherein the images are divided into pre-determined sections and wherein the method further comprising the steps of:
 aligning and linking the scanned images,   automatically comparing the colour data for each section of one image with the colour data for a linked corresponding section of the other image to determine whether any differences exceed a pre-determined threshold and maintaining a count indicative of the number of sections which are determined to exceed such threshold, and,   determining whether the number of sections which exceed such threshold exceeds a pre-determined overall threshold to determine colour quality.   
     
     
         7 . The method of  claim 6  wherein the images are comprised of pixels and the sections are individual pixels. 
     
     
         8 . The method of  claim 6  wherein the images are comprised of pixels, the sections comprise groups of pixels and the colour data for a section is a calculated average of the colour data for the pixels in said section. 
     
     
         9 . The method of  claim 8  further comprising the additional steps of:
 selecting a portion of one of the scanned images,   automatically selecting a corresponding portion of the other of the scanned images,   calculating an average for the colour data associated with said selected portions,   calculating the difference between the averages, and,   comparing the difference to a pre-determined threshold to determine colour quality.   
     
     
         10 . A method of printing colour products on a colour printing press, which has associated with it a certain press fingerprint comprised of the values for all relevant print variables under press operating conditions, in a print run associated with a contract proof, the method comprising the steps of:
 scanning the contract proof to create image data including colour data representing a scanned proof image,   removing a sample printed colour product from the press,   scanning the printed colour product to create image data including colour data representing a scanned press pull image,   displaying the scanned images simultaneously on a video monitor,   aligning and linking the scanned images,   automatically comparing the colour data for each section of one image with the colour data for a linked corresponding section of the other image to determine whether any differences exceed a pre-determined threshold and maintaining a count indicative of the number of sections which are determined to exceed such threshold,   determining whether the number of sections which exceed such threshold exceeds a pre-determined overall threshold to determine colour quality,   if the overall threshold is not exceeded, continuing with the print run,   if the overall threshold is exceeded, temporarily stopping the print run, adjusting the print variables, resuming the print run, and,   repeating the above from the removing sample step until the print run is complete.   
     
     
         11 . A system for analyzing the colour quality of a press pull as compared to a contract proof comprising:
 at least one scanner for scanning the contract proof to create image data including colour data representing a scanned proof image and for scanning the press pull to create image data including colour data representing a scanned press pull image,   an image comparator connected to the at least one scanner to receive the data for the scanned proof image and the scanned press pull image,   a video monitor connected to the image comparator to receive the data for the scanned proof image and the scanned press pull image and to display the scanned images simultaneously.   
     
     
         12 . A system as claimed in  claim 11  wherein the system further comprises an input device whereby a user may select corresponding portions of the scanned images and wherein the comparator is operable to calculate an average for the colour data associated with said selected portions, to calculate the difference between the averages, and, to compare the difference to a pre-determined threshold to determine colour quality. 
     
     
         13 . A system as claimed in  claim 11  wherein the images are divided into pre-determined sections and the comparator is operable to align and link the scanned images, to automatically compare the colour data for each section of one image with the colour data for a linked corresponding section of the other image to determine whether any differences exceed a pre-determined threshold and to maintain a count indicative of the number of sections which are determined to exceed such threshold, and, to determine whether the number of sections which exceed such threshold exceeds a pre-determined overall threshold to determine colour quality. 
     
     
         14 . A system as claimed in  claim 13  wherein the comparator is operable to receive information identifying user selection of a portion of one of the scanned images, to automatically select a corresponding portion of the other of the scanned images, to calculate an average for the colour data associated with said selected portions, to calculate the difference between the averages, and, to compare the difference to a pre-determined threshold to determine colour quality. 
     
     
         15 . The method of  claim 1  wherein the video monitor is remotely located from the location of the press pull and the method further comprises communicating the results of the searching for differences and the evaluation thereof back to the location of the press pull.