Error Diffusion Control Device Using Modified Evaluated Density
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Solution Overview
Problem
Conventional error diffusion processes in inkjet printing often result in excessively high dot density in printed images due to small values used to specify dot density, leading to inaccuracies in representing the original image.
Innovation Solution
A control process that determines dot values and distribution error values for each pixel using gradation values, error values, and threshold values, adjusting the evaluated density values based on ink ejection properties to prevent excessive error distribution and maintain original image density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If small values are used to specify dot density in error diffusion process, then dot formation accuracy is improved, but printed image density becomes excessively high
Solution Approach 1:
The patent dynamically changes the threshold value parameter based on the accumulated error value. When the error value exceeds a predetermined threshold, the threshold value is increased to prevent excessive dot formation. This parameter adaptation resolves the contradiction by allowing small threshold values for accuracy when errors are low, while increasing the threshold to control density when errors accumulate.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the accumulated error value and adjusting the threshold value accordingly. The error value calculated from the difference between original image density and printed image density feeds back into the decision-making process for subsequent pixels, enabling real-time correction of density deviations while maintaining dot formation accuracy.
2Manufacturing precision
If error value is distributed to unprocessed pixels, then image quality is improved, but density in parts of printed image becomes higher than original image
Solution Approach 1:
The patent changes the threshold parameter dynamically based on error magnitude. For pixels with large accumulated error values, the threshold is increased to suppress dot formation and prevent density overshoot. This allows error diffusion to improve image quality in most areas while controlling density in regions where error accumulation would otherwise cause excessive darkness.
Solution Approach 2:
The patent applies preliminary anti-action by anticipating potential density overshoot before it occurs. When the accumulated error value exceeds a predetermined threshold, the system proactively increases the threshold value to counteract the tendency toward excessive dot formation, thereby preventing density from exceeding the original image levels before the problem manifests.
Data Source
AI summary
In an error diffusion process, a control device determines a dot value of a target pixel by using a gradation value of the target pixel, and an error value. The control device determines distribution error value by comparing a gradation dependent value with a first evaluated density value indicating a density of a first dot. The control device determines the distribution error value by using the first evaluated density value when the dot value of the target pixel indicates formation of the first dot and when the gradation dependent value is smaller than or equal to the first evaluated density value. The control device determines the distribution error value by using a modified evaluated density value greater than the first evaluated density value when the dot value indicates formation of the first dot and when the gradation dependent value is greater than the first evaluated density value.