Toner Adhesion Limiting Circuit for Smooth Gradation Control
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Solution Overview
Problem
Existing methods for limiting toner adhesion in color image forming apparatuses cause rapid gradation changes near the threshold value, degrading image quality.
Innovation Solution
Converting image data for each color plane into first amount-of-toner-adhesion data, using a preset threshold value table to limit toner adhesion, and then converting this data into image signals, allowing for arbitrary parameter setting to suppress rapid gradation changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the sum total of CMYK image signal values is limited to a threshold value (e.g., 250%), then the amount of toner adhesion is reduced to prevent detachment and unnecessary remaining, but rapid suppression of gradation occurs when pixel values are near the threshold, degrading image quality
Solution Approach 1:
The patent applies parameter changes by using a non-linear conversion function (equation 1) that dynamically adjusts the limiting threshold based on the input signal value. When the input value is below the threshold, no limiting is applied. When it exceeds the threshold, the output is calculated using a formula that creates a gradual transition: output = threshold - (input - threshold) × (threshold / input). This parameter-based approach replaces the abrupt binary limiting with a continuous, smooth transition that maintains gradation while still limiting toner adhesion.
Solution Approach 2:
The patent implements dynamics by making the limiting threshold adaptive rather than fixed. The effective threshold dynamically adjusts based on the input signal value through the conversion equation. As the input value changes, the limiting behavior automatically adapts: for values close to the threshold, the output smoothly approaches the threshold without abrupt changes; for values far above the threshold, the limiting effect becomes more pronounced. This dynamic approach prevents rapid gradation suppression while maintaining toner adhesion control.
2Device complexity
If a fixed threshold value is used for toner limiting, then the limiting process is simple, but rapid gradation change occurs near the threshold value causing image quality degradation
Solution Approach 1:
The patent changes the parameter approach from a fixed threshold to a dynamic threshold that varies with the input signal value. The conversion equation output = threshold - (input - threshold) × (threshold / input) creates an adaptive threshold effect where the effective limiting point shifts based on the input magnitude. This parameter transformation maintains computational simplicity (still a single equation) while eliminating the abrupt gradation changes associated with fixed thresholding.
Solution Approach 2:
The patent introduces an intermediary conversion function that mediates between the input image signal and the output limited signal. Rather than directly comparing and clipping values at a fixed threshold, the conversion equation acts as an intermediary that smoothly transitions values near the threshold. This intermediary function prevents the abrupt discontinuity that causes rapid gradation suppression, while still achieving the desired toner adhesion limitation.
Data Source
AI summary
Even when an image signal is converted into an image signal with a limited amount of toner adhesion, the gradation is prevented from changing rapidly near the limiting value and therefore the image quality is prevented from deteriorating. An amount-of-adhesion converting circuit 301 converts image data for each color plane into first amount-of-toner-adhesion data. On the basis of a preset amount-of-toner-adhesion threshold value table, an amount-of-toner-adhesion reduction computing circuit 303 converts the first amount-of-toner-adhesion data for each color plane into second amount-of-toner-adhesion data with a limited amount of toner adhesion. Then, an image signal converting circuit 304 converts the second amount-of-toner-adhesion data into an image signal. In such a method, since parameters in the amount-of-toner-adhesion threshold value table are set arbitrarily, a rapid change in gradation can be suppressed near the limiting value.