Global Tone Mapping with Chroma Boost for Low-Light Images
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Solution Overview
Problem
Traditional global tone mapping techniques adjust image brightness while suppressing chrominance channels, leading to overexposure and color loss, particularly in low-light conditions, resulting in unnatural image appearances.
Innovation Solution
The method involves determining a cumulative distribution function (CDF) histogram from the luminance channel of an input image, identifying the closest entry CDF histogram in a lookup table, and applying a Y channel global tone mapping curve, followed by a chroma tone mapping curve to enhance brightness with minimal contrast loss and boost colors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If traditional luminance channel global tone mapping is applied to adjust image brightness, then image brightness is improved, but chrominance channels are suppressed leading to color loss
Solution Approach 1:
The patent segments the tone mapping process into separate luminance and chrominance channels. The luminance channel (Y) undergoes global tone mapping to adjust brightness, while the chrominance channels (Cb, Cr) are processed independently through chroma boost to enhance colors. This segmentation allows brightness adjustment without suppressing chrominance information.
Solution Approach 2:
The patent applies different processing quality to different channels: the luminance channel receives global tone mapping for brightness optimization, while the chrominance channels receive chroma boost for color enhancement. This local quality differentiation ensures that each channel is optimized for its specific function without compromising the other.
2Illumination intensity
If global tone mapping is applied to enhance brightness, then image brightness is improved, but contrast is lost
Solution Approach 1:
The patent changes the parameters of the tone mapping curve dynamically based on the input image's luminance histogram. By analyzing the histogram and selecting appropriate curve parameters, the system achieves brightness enhancement while preserving contrast. The chroma boost operation further enhances colors without affecting the luminance-contrast relationship.
3Illumination intensity
If traditional tone mapping is applied to low-light images, then brightness is improved, but natural appearance is degraded due to overexposure
Solution Approach 1:
The patent uses feedback from the luminance histogram analysis to adapt the tone mapping curve parameters. The system continuously adjusts the mapping based on the image content to achieve natural-looking results. The chroma boost operation also provides feedback to maintain color naturalness while enhancing brightness.
Data Source
AI summary
An apparatus includes at least one processing device configured to obtain an input image and determine a cumulative distribution function (CDF) histogram from a luminance or luma (Y) channel of the input image. The at least one processing device is also configured to determine an entry CDF histogram in a CDF histogram lookup table (LUT) closest to the determined CDF histogram. The at least one processing device is further configured to apply a Y channel global tone mapping (GTM) curve to the input image based on one or more parameters assigned to the entry CDF histogram from the CDF histogram LUT.