Image Processing Edge Detection for Inkjet Density Uniformity
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Solution Overview
Problem
Image quality is deteriorated due to density unevenness caused by variations in ejection characteristics among nozzles in inkjet recording heads, particularly affecting the linearity of edges in character or line drawings when conventional head shading processing reduces the number of ink dots.
Innovation Solution
An image processing apparatus that detects edge information and adjusts the processing to increase or reduce color signals of edge pixels to a lesser degree than non-edge pixels, preventing the deterioration of image quality by maintaining linearity at edges while reducing density differences between nozzle groups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If head shading processing is applied to reduce density unevenness by adjusting the number of ink dots per nozzle, then density uniformity across the image is improved, but edge linearity and character quality deteriorate due to excessive dot reduction at edge regions
Solution Approach 1:
The patent applies different processing strategies to different regions of the image based on edge detection results. Edge regions are identified through gradient calculation, and the head shading processing is modified to reduce or eliminate dot reduction in these regions, while non-edge regions continue to receive full head shading processing. This local differentiation maintains edge linearity while still achieving density uniformity in appropriate areas.
Solution Approach 2:
The image is segmented into edge regions and non-edge regions through gradient calculation and thresholding. This segmentation allows the processing system to apply different correction strengths to different segments, preserving the sharpness of edges while correcting density unevenness in interior regions.
2Manufacturing precision
If the number of ink dots is reduced uniformly across all regions to compensate for high ejection amount nozzles, then density differences between nozzle groups are reduced, but image quality at edges and lines deteriorates
Solution Approach 1:
The patent implements location-dependent head shading processing where the correction amount is modulated by edge information. In edge regions detected through gradient analysis, the dot reduction is minimized or eliminated to preserve image quality, while in non-edge regions, full correction is applied to achieve density consistency. This creates a spatially varying correction profile that adapts to local image characteristics.
Data Source
AI summary
An image processing apparatus includes a processing unit that converts first input image data for a first region and second input image data for a second region to reduce a difference between first region recorded image density and second region recorded image density, and generates dot position data of a dot to be generated in each of the first and second regions based on the dot data after the conversion processing. The acquisition unit acquires edge information indicating a first object pixel edge of an image pixel for the first region and a second object pixel edge of an image pixel for the second region. Based on the acquired edge information, conversion and generation processing are performed in such a manner that a color signal of an edge pixel is increased/reduced to a degree lower than a degree to which a color signal of a non-edge object pixel is increased/reduced.