Image Processing Apparatus Reducing Banding in Subsampled Images
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Solution Overview
Problem
Subsampled images, particularly those with chrominance signals thinned out, often exhibit banding artifacts due to simple interpolation methods, leading to degradation in image quality, especially at color edges.
Innovation Solution
An image processing apparatus and method that calculates a correction target signal global gain and luminance local slope for each pixel, multiplying the local slope by the global gain to correct pixel values, thereby reducing banding and enhancing image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If chrominance signals are thinned out to reduce data amount, then data transmission efficiency is improved, but image quality deteriorates due to banding artifacts
Solution Approach 1:
The patent changes the interpolation parameter from simple adjacent pixel copying to a calculated value based on luminance signal slopes. By computing the correction value as the product of luminance local slope and chrominance global gain, the patent transforms the interpolation approach to maintain color gradient smoothness while preserving data reduction benefits
Solution Approach 2:
The patent introduces the luminance signal slope as an intermediary parameter to mediate between the thinned chrominance signals and the final interpolated values. This intermediary allows the system to use luminance information (which is fully sampled) to guide chrominance interpolation, thereby reducing banding artifacts while maintaining the subsampled structure
2Speed
If simple interpolation is used to fill missing chrominance pixels, then processing speed is improved, but image quality deteriorates due to banding at color edges
Solution Approach 1:
The patent modifies the interpolation parameter calculation from direct adjacent pixel copying to a computed value using luminance slope and chrominance global gain. This parameter change introduces additional calculation steps that improve image quality by reducing banding, while the localized nature of the calculation (using only nearby pixels) maintains relatively high processing speed
3Quantity of substance
If chrominance signals are subsampled by a factor of 4, then data amount is reduced significantly, but interpolation accuracy deteriorates leading to visible banding
Solution Approach 1:
The patent uses the luminance signal as an intermediary to improve chrominance interpolation accuracy. Since luminance is fully sampled and contains detailed spatial information, its slope serves as a reliable guide for reconstructing chrominance values at missing positions, thereby compensating for the aggressive 4x subsampling
Solution Approach 2:
The patent changes the interpolation parameter from simple adjacent pixel copying to a calculated value based on luminance signal slopes. By computing the correction value as the product of luminance local slope and chrominance global gain, the patent transforms the interpolation approach to maintain color gradient smoothness even with aggressive subsampling
Data Source
AI summary
An apparatus and a method that decrease a banding phenomenon in a subsampled image and achieve high image quality are provided. A subsampled image obtained by copying an adjacent pixel value to a pixel value thinning position is accepted as an input image; a correction target signal global gain is calculated as a ratio between a slope of a correction target signal and a slope of a luminance signal of a global region made up of a plurality of consecutive pixels including a pixel position of the correction target pixel of the input image; a luminance local slope is calculated as a slope of the luminance signal of a local region which is a region within the global region, including the pixel position of the correction target pixel of the input image and smaller than the global region; and a corrected pixel value of the correction target pixel is calculated.