Local Color Correction in Offset Printing via Digital Halftone Adjustment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Offset printing machines face inefficiencies in correcting local inking errors due to the need for pre-compensation using test forms and extra printing plates, which increases time and cost, making the color control process less productive.
Innovation Solution
A method using a computer-based image acquisition system to record print images, determine local delta values for halftone corrections, and modify screen tone values for subsequent print jobs, eliminating the need for test forms and enabling continuous improvement of color control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pre-compensation is performed using test forms and additional printing plates, then local color deviations can be corrected, but time and cost increase, reducing productivity
Solution Approach 1:
The invention uses a digital copy (electronic test form data) instead of physical test forms. The image acquisition system captures test form prints and converts them to digital data, which is then processed to generate correction values. This digital copying eliminates the need to physically print, analyze, and evaluate test forms, thereby removing the productivity bottleneck while maintaining color accuracy correction capabilities
Solution Approach 2:
The system performs preliminary determination of local color characteristics during the printing of test forms as part of normal production. The correction values are calculated and stored in advance, so when actual print jobs are executed, the corrections are already prepared and can be applied immediately without additional setup time, thus maintaining both precision and productivity
2Manufacturing precision
If ink zones are used for color control perpendicular to printing direction, then local color variations can be controlled, but precise compensation of very small color variations is difficult due to minimum zone size
Solution Approach 1:
The invention implements local quality by determining color characteristics for individual pixels or small groups of pixels rather than using large ink zones. The image acquisition system captures high-resolution test form data, and the computer processes this data to generate correction values for each local area independently. This allows precise compensation for even very small color variations while maintaining the ability to control local color uniformity
Solution Approach 2:
The printing press is segmented into multiple local correction zones corresponding to different printing units and color separations. The image acquisition system divides the test form image into corresponding regions, and correction values are calculated separately for each region. This segmentation allows independent optimization of each printing unit's color characteristics, enabling precise control of local color variations without being constrained by minimum ink zone sizes
3Loss of information
If test forms are printed and evaluated to determine color characteristics, then local color deviations can be identified, but additional printing plates and analysis time are required
Solution Approach 1:
The invention replaces the mechanical/physical analysis process with an automated digital system. Instead of physically printing test forms, manually analyzing prints, and evaluating color characteristics, the system uses an image acquisition system to capture test form images, a computer to automatically process the digital data, and algorithms to determine color characteristics. This substitution eliminates manual labor and physical handling, significantly reducing time loss while ensuring complete capture of color characteristic information
Solution Approach 2:
The system implements automated feedback by continuously capturing test form print images during normal operation, automatically comparing them against target values, and generating correction values that are fed back into the printing process. This closed-loop feedback system eliminates the need for separate analysis and evaluation steps, as the correction values are automatically determined and applied, reducing both time loss and information loss
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Method for correcting local, machine-induced coloring defects in an offset printing press (4) with an image acquisition system (2) by a computer (3, 6), which performs the steps of capturing print images (12) during the processing of at least one print job by the image acquisition system (2), performing a color transformation for the captured print images (12) by the computer (3, 6), determining local delta values (14) for halftone values by the computer (3, 6) from the color-transformed image data (13), correcting the delta values (9) for the halftone values depending on the ink coverage by the computer (3, 6), reading and analyzing print job-specific influencing parameters (8) from the control of the offset printing press by the computer (3, 6), and determining correction values (10) for the local,machine-induced coloring errors from the corrected delta values (9) for the halftone values and the print-job-specific influencing parameters (8) by the computer (3, 6), the modification of the halftone values of subsequent print jobs with the determined correction values (10) by the computer (3, 6) and the production of printing plates with the modified halftone values and the execution of the print jobs with the produced printing plates, are included.