Image Sensor Tone Correction for Luminance Distribution Analysis
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Solution Overview
Problem
Existing tone correction methods often result in image quality deterioration, either by losing contrast in intermediate luminance regions or producing unnatural images with excessive contrast, particularly in scenes with white objects or backlight conditions.
Innovation Solution
An image sensing apparatus and method that applies tone correction based on luminance distribution analysis, using multiple correction units to suppress saturation, adjust maximum luminance values, and apply gain to low-luminance regions, while limiting concurrent corrections to prevent overcorrection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If tone correction is applied using the tone curve so that an image dark part is corrected to be brighter, then the brightness of dark regions is improved, but the contrast in intermediate luminance region is lost resulting in a flat image
Solution Approach 1:
The patent applies different gain values to different luminance regions. Specifically, it sets a first gain for low-luminance regions, a second gain for intermediate luminance regions, and a third gain for high-luminance regions. This local quality approach ensures that dark regions are brightened while preserving the contrast characteristics of intermediate luminance regions, thereby resolving the contradiction between improving dark region brightness and maintaining intermediate region contrast.
2Illumination intensity
If tone correction is applied using low-frequency component signals of luminance components, then dark objects are made brighter while maintaining image contrast, but too much contrast is obtained depending on scenes resulting in an unnatural image
Solution Approach 1:
The patent dynamically adjusts the gain values based on the luminance distribution characteristics of the input image. By calculating the luminance distribution and determining appropriate gain values adaptively, the system avoids applying excessive contrast enhancement that would result in unnatural images. This dynamic adjustment allows the tone correction to be suited to different luminance distributions, resolving the contradiction between brightening dark objects and maintaining image naturalness.
3Illumination intensity
If multiple tone correction methods are applied simultaneously, then comprehensive tone adjustment is achieved, but overcorrection occurs resulting in image quality deterioration
Solution Approach 1:
The patent employs a feedback mechanism where the luminance distribution of the input image is analyzed first, and based on this analysis, appropriate gain values are determined and applied. The system monitors the luminance distribution characteristics and adjusts the tone correction parameters accordingly, preventing overcorrection. This feedback-based approach ensures that multiple tone correction methods are applied in a controlled manner, maintaining image quality while achieving comprehensive tone adjustment.
Data Source
AI summary
An image sensing apparatus executes a plurality of tone corrections respectively suited to different luminance distributions of images. The image sensing apparatus analyzes a luminance distribution of sensed image data, selects, based on an analysis result, at least one of a first tone correction which suppresses luminance saturation of image data, a second tone correction which converts luminance values of all luminance regions so that a maximum luminance value of sensed image data becomes a largest possible luminance value of the image data, and a third tone correction which multiplies a luminance value of a low-luminance region, which is set in advance, of sensed image data by a gain larger than gains of other luminance regions, as a tone correction to be implemented for sensed image data, and limits, when a correction based on the second tone correction is selected, implementation of a correction based on the third tone correction.