Image Processing Apparatus Tone Conversion Chroma Preservation
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Solution Overview
Problem
Existing image processing technologies face challenges in tone conversion for images with multiple color signals, as gamma conversion can alter chroma and hue, leading to undesirable changes, especially in high-luminance regions where chroma is decreased and colors may approach achromatic tones.
Innovation Solution
An image processing apparatus and method that performs signal enhancement based on signal values without changing chroma and hue, followed by tone conversion using a weak gamma conversion curve, which has a lower degree of gamma enhancement than standard curves, ensuring that signal values in halftone regions remain within an appropriate output range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If gamma conversion is performed with respect to multiple color signals to perform tone conversion, then tone conversion is achieved, but chroma and hue change
Solution Approach 1:
The patent divides the image into multiple luminance regions (first luminance region with higher luminance and second luminance region with lower luminance) and applies different gamma conversion curves to each region. This segmentation allows the high-luminance region to use a curve that preserves chroma while the low-luminance region uses a curve that enhances tone, thereby resolving the contradiction between tone conversion accuracy and chroma preservation.
Solution Approach 2:
The patent applies different gamma conversion characteristics to different parts of the image based on their luminance levels. Specifically, a first gamma conversion curve with a smaller slope is applied to the high-luminance region to preserve chroma, while a second gamma conversion curve with a larger slope is applied to the low-luminance region to enhance tone. This local differentiation resolves the contradiction by optimizing for different priorities in different regions.
2Manufacturing precision
If a standard gamma conversion curve is used to enhance halftone region signal values, then output signal values become appropriate, but chroma decreases in high-luminance regions
Solution Approach 1:
The patent segments the luminance range into two distinct regions and applies different gamma conversion curves to each. The first gamma conversion curve is designed with a smaller slope specifically for the high-luminance region to minimize chroma loss, while the second curve with a larger slope handles the low-luminance region to ensure proper halftone enhancement. This segmentation resolves the contradiction by allowing each region to be optimized for its specific requirements.
Solution Approach 2:
The patent changes the gamma conversion parameter (slope of the conversion curve) based on the luminance region. By using a smaller slope for high-luminance regions and a larger slope for low-luminance regions, the patent dynamically adjusts the conversion characteristics to preserve chroma where needed while enhancing tones where required, thereby resolving the contradiction between output accuracy and chroma preservation.
Data Source
AI summary
An image processing apparatus includes: a gain calculating portion and a gain multiplication portion that perform signal enhancement with respect to an input image constituted by pixels having a plurality of color signals, with an intensity in accordance with signal values of each pixel, without changing a chroma and a hue; and a gamma correction portion that performs, for each pixel, tone conversion of a plurality of color signals that are subjected to signal enhancement, based on a weak gamma conversion curve in which a degree of gamma enhancement is weaker than in a basic gamma conversion curve which performs conversion such that a signal value of a halftone region at a time of outputting in a case where signal enhancement is not performed becomes a signal value in an appropriate output value range.