Image Correction Unit Banding Reduction via Error Diffusion
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Solution Overview
Problem
Existing image forming apparatuses using electrophotographic systems face issues with density unevenness, known as banding, due to rotation unevenness in components like photosensitive drums and development rollers, leading to poor print quality and insufficient correction accuracy when using methods like density and position correction after halftone processing.
Innovation Solution
An image forming apparatus with a correction amount determination unit, image correction unit, and quantization unit that determines and applies correction amounts to pixel values of an image signal to correct banding as periodic density unevenness, and diffuses quantization errors across a main scanning direction to minimize their impact within a predetermined region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of bits of an image signal is reduced after halftone processing to reduce data transfer amount and save memory, then data transfer efficiency and memory usage are improved, but correction accuracy deteriorates due to insufficient resolution to reflect correction amounts
Solution Approach 1:
The patent applies error diffusion by redirecting quantization errors from the sub-scanning direction (where they cause visible banding) to the main scanning direction (where they are less perceptible). This dimensional transformation of error distribution allows reduced bit depth while maintaining correction accuracy, as the errors are redistributed rather than simply reduced.
Solution Approach 2:
The patent converts the harmful quantization errors that would normally degrade image quality into a beneficial error diffusion process. By deliberately diffusing these quantization errors in the main scanning direction, the patent transforms what would be visible defects into an acceptable trade-off that enables reduced data representation while maintaining perceived image quality.
2Measurement precision
If banding image correction is performed after halftone processing to ensure correction effectiveness, then banding correction accuracy is improved, but the number of bits required for the image signal increases
Solution Approach 1:
The patent redirects quantization errors from the sub-scanning direction to the main scanning direction through error diffusion. This allows the use of fewer bits (4-bit instead of 8-bit) while maintaining correction accuracy, as the errors are redistributed in a direction that is less perceptible to human vision.
Solution Approach 2:
The patent transforms quantization errors that would normally degrade image quality into a beneficial error diffusion mechanism. By deliberately diffusing these errors in the main scanning direction, the patent enables reduced data transfer amount and memory usage while maintaining acceptable image quality and correction effectiveness.
3Productivity
If quantization is applied to reduce bit depth of corrected image signal, then data transfer efficiency is improved, but quantization errors are generated that can cause horizontal streaks and deteriorate image quality
Solution Approach 1:
The patent extracts and separates quantization errors from their harmful context (sub-scanning direction where they cause banding) and relocates them to a less harmful context (main scanning direction where they cause less perceptible artifacts). This extraction and redistribution approach maintains data efficiency while minimizing image quality degradation.
Solution Approach 2:
The patent transforms the spatial distribution of quantization errors by diffusing them in the main scanning direction rather than allowing them to manifest in the sub-scanning direction. This dimensional redirection converts harmful concentrated errors into less perceptible distributed errors, improving overall image quality despite quantization.
Data Source
AI summary
An image forming apparatus of this invention determines a correction amount for each image signal so as to correct banding as periodic density unevenness in a sub scanning direction, corrects each pixel value of an n-bit image signal in accordance with the correction amount, generates the first corrected image signal, and quantizes, for each pixel, the first corrected image signal into a second corrected image signal of m bits smaller than n bits. This image forming apparatus diffuses, in a main scanning direction, quantization errors at the time of quantization of the first corrected image signal into the second corrected image signal so as to cancel the quantization errors within a predetermined region including a plurality of continuous pixels on a main scanning line.