Halftone Processing Control for Graininess Suppression
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Solution Overview
Problem
Existing halftone techniques, such as error diffusion and dithering methods, suffer from worsening graininess when handling image data with mid- and high-frequency components, particularly in printing technologies like ink jet printers, which introduces noise and affects image quality, especially during reflective document copying.
Innovation Solution
An image processing apparatus that dynamically adjusts the application levels of dithering and error diffusion methods based on data gradation values and high-frequency component analysis, reducing graininess by preferentially using error diffusion for high-frequency data and dithering for low-frequency data, and controlling the error diffusion threshold to optimize dot formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the error diffusion method is used for halftone processing, then fine lines at low densities are reproduced well, but graininess worsens significantly when the image data contains mid- and high-frequency components
Solution Approach 1:
The patent segments the halftone processing into two distinct methods: ordered dithering method for regions with high-frequency components and error diffusion method for regions with low-frequency components. This segmentation allows each method to be applied optimally to its respective region, preventing the graininess issue that occurs when error diffusion is applied uniformly across the entire image.
Solution Approach 2:
The patent applies different halftone processing characteristics to different regions of the image data based on their frequency content. High-frequency regions use ordered dithering to maintain fine line reproduction, while low-frequency regions use error diffusion to optimize graininess. This local differentiation resolves the contradiction by making the processing quality adapt to local image characteristics.
2Reliability
If the dithering method with blue noise mask characteristics is used, then graininess is suppressed in areas with landing position skew, but low-density fine lines break or disappear and graininess worsens when image data contains mid- and high-frequency components
Solution Approach 1:
The patent divides the image processing into two segments: one using ordered dithering for high-frequency regions where fine line reproduction is critical, and another using error diffusion for low-frequency regions where graininess suppression is important. This segmentation prevents the blue noise mask dithering from degrading fine line quality while maintaining its robustness to landing position skew in appropriate regions.
Solution Approach 2:
The patent assigns different processing qualities to different spatial locations based on their frequency characteristics. Regions with high-frequency components receive ordered dithering processing to preserve fine line integrity, while regions with low-frequency components receive error diffusion processing to optimize overall graininess. This local quality assignment resolves the contradiction between robustness and fine line reproduction.
3Adaptability or versatility
If a combination of error diffusion and dithering methods is applied with gradual transition, then both low-density fine lines and high-density areas are handled well, but graininess worsens slightly in transition areas
Solution Approach 1:
The patent implements clear segmentation between error diffusion and ordered dithering regions based on frequency thresholding. Instead of a gradual transition that creates intermediate problematic zones, the patent establishes distinct regions with clear boundaries, eliminating the graininess worsening that occurs in gradual transition areas while maintaining adaptability to different density regions.
Solution Approach 2:
The patent uses frequency threshold parameters to determine the boundaries between different halftone processing regions. By changing the processing method parameter based on frequency content rather than using gradual blending, the patent achieves sharp transitions that avoid the graininess worsening associated with gradual transitions, while still providing versatile handling of different image regions.
Data Source
AI summary
An image processing apparatus that prints an image includes a preliminary halftone processing unit configured to determine whether a preliminary dot through a dithering method is to be formed, a final halftone processing unit configured to determine whether a dot to be printed through an error diffusion method is to be formed, and a dither result application level control unit configured to control a dither result application level which is a level at which probability that the dot to be printed will be formed is raised with the final halftone processing unit when the preliminary dot is to be formed in the preliminary halftone processing unit. The dither result application level control unit reduces the dither result application level during printing in a case of copying a reflected document or a case where the image data contains many high-frequency components, compared to other instances of printing.