Image Processing Gain Adjustment for Contrast Enhancement
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Solution Overview
Problem
Local tone mapping techniques often reduce image contrast compared to global tone mapping, particularly when using tone characteristics where the gain value monotonically increases with luminance, leading to suboptimal image enhancement.
Innovation Solution
An image processing apparatus that generates reference gain information based on a first tone characteristic and corrects it using a second tone characteristic where the gain signal monotonically decreases or increases uniformly, regardless of the luminance range, to improve image contrast through gain processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If local tone mapping processing is performed using a tone characteristic where the gain signal monotonically increases with luminance, then image enhancement is achieved, but the image contrast is reduced compared to global tone mapping
Solution Approach 1:
The patent divides the gain adjustment process into two distinct stages: first generating reference gain information based on a monotonic tone characteristic, then correcting it with a non-monotonic correction signal. This segmentation allows each stage to fulfill its specific function - the reference gain provides baseline enhancement while the correction signal restores contrast, resolving the contradiction between enhancement quality and contrast preservation.
Solution Approach 2:
The patent changes the parameter characteristics by using two different tone characteristics: a first tone characteristic with monotonic gain increase for reference gain generation, and a second tone characteristic with non-monotonic gain variation for correction. This parameter change strategy enables the system to achieve both image enhancement and contrast preservation by appropriately selecting different gain characteristics for different processing stages.
2Manufacturing precision
If a first tone characteristic with monotonic gain increase is used for reference gain generation, then image enhancement is achieved, but contrast reduction occurs
Solution Approach 1:
The patent introduces a correction signal as an intermediary element that mediates between the reference gain information and the final gain applied to the image. This correction signal, generated based on a second tone characteristic, acts as a bridge that preserves the enhancement benefits of the first tone characteristic while compensating for its contrast-reducing effect, thus resolving the contradiction.
Solution Approach 2:
The patent employs parameter changes by switching from a monotonic tone characteristic for reference gain to a non-monotonic tone characteristic for correction. This change in gain characteristics allows the system to first achieve enhancement with the monotonic characteristic, then restore contrast using the non-monotonic correction, effectively resolving the contradiction between enhancement accuracy and luminance contrast.
Data Source
AI summary
Image processing generates reference gain information based on a first tone characteristic by using an input image, the reference gain information including a gain value corresponding to a luminance value for each pixel, the first tone characteristic including a luminance range in which a gain signal monotonically increases; generates a correction signal to correct the reference gain information based on a second tone characteristic in which the gain signal monotonically decreases or monotonically increases regardless of the luminance range by using the input image and a low-frequency image generated from the input image; and performs gain processing on the input image based on gain information obtained after the reference gain information is corrected by the correction signal.