Defective Nozzle Compensation in Inkjet Printers
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Solution Overview
Problem
Inkjet printers face discharge failures due to nozzle clogging or ink drying, leading to image quality degradation, as existing compensation methods are inadequate in addressing defective nozzles effectively.
Innovation Solution
An image forming apparatus and method that includes a threshold comparator and two image compensators to identify and compensate for defective nozzles by setting discharge values and spreading quantization errors to neighboring pixels, and replacing smaller dots with larger ones using pattern matching, based on pixel values and nozzle conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing compensation methods are used for defective nozzles, then some image quality degradation is addressed, but the compensation is inadequate and image quality still deteriorates
Solution Approach 1:
The patent changes the parameter of compensation strength based on the pixel value magnitude. For pixels with values below a predetermined threshold, stronger compensation is applied by spreading quantization errors to neighboring pixels. For pixels with values at or above the threshold, weaker compensation is applied by only replacing smaller dots with larger dots. This adaptive parameter change resolves the contradiction by making the compensation method versatile enough to handle different image regions effectively.
Solution Approach 2:
The patent implements dynamic compensation by selecting different compensation strategies based on real-time pixel value conditions. The system dynamically adjusts the compensation approach: using error diffusion for low-value pixels and dot replacement for high-value pixels. This dynamic adaptation ensures reliable image quality across varying image content while maintaining compensation effectiveness.
2Reliability
If quantization error is spread to neighboring pixels for all defective nozzle cases, then image quality is improved, but unnecessary processing is performed on high-value pixels where it is less effective
Solution Approach 1:
The patent introduces a parameter-based decision mechanism using a predetermined threshold to control the compensation approach. When pixel values exceed the threshold, the system switches from error diffusion to dot replacement processing. This parameter-driven strategy improves image quality where needed while reducing unnecessary processing complexity for high-value pixels, resolving the contradiction between reliability and device complexity.
3Reliability
If dot replacement is performed for all pixels, then high-value regions are compensated, but low-value regions require stronger compensation that dot replacement cannot provide
Solution Approach 1:
The patent applies the principle of local quality by tailoring the compensation method to the specific characteristics of different pixel regions. Low-value pixels receive error diffusion compensation which is suitable for subtle tone variations, while high-value pixels receive dot replacement compensation which is effective for prominent dots. This localized approach ensures adaptability across different image regions while maintaining overall image quality reliability.
Solution Approach 2:
The patent uses parameter changes by switching between two distinct compensation modes based on pixel value thresholds. The system changes the compensation parameter from error diffusion (for values below threshold) to dot replacement (for values at or above threshold). This parameter-based adaptability resolves the contradiction by ensuring the right compensation technique is applied to each region, achieving both reliability and versatility.
Data Source
AI summary
An image forming apparatus includes an image forming device, a threshold comparator, a first image compensator, and a second image compensator. The first compensator executes a processing of, for at least a pixel value less than a threshold, setting a value of stopping discharge of a droplet from a defective nozzle in converting multi-valued data of an input image into n-value data, and spreading a quantization error due to setting the value, to neighboring pixels of a pixel corresponding to a defective nozzle. The second compensator executes a processing of replacing a smaller dot among dots around the defective nozzle with a larger dot by pattern matching using a mask pattern in accordance with a dot size and placement around the defective nozzle, on condition that as a result of comparison of the comparator, the pixel value corresponding to the defective nozzle is equal to or more than the threshold.