Image Synthesis Using Luminance-Based Weighting for Dynamic Range
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Solution Overview
Problem
Conventional methods for synthesizing images under different exposure conditions often result in low contrast and chroma changes, leading to unnatural images with decreased dynamic range.
Innovation Solution
An image processing apparatus that performs low-pass processing and gradation conversion on images captured under different exposure conditions to generate a synthetic image with a higher dynamic range, using a decision unit to determine weighting amounts for synthesis, thereby minimizing contrast and chroma changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If different gradation curves are used for synthesis according to input signal level, then dynamic range is improved, but contrast and chroma deteriorate
Solution Approach 1:
The patent segments the image into multiple regions based on luminance levels (highlight, intermediate, shadow regions) and applies different processing to each region. By dividing the image processing into distinct luminance-based segments, the system can preserve contrast and chroma in each region while achieving extended dynamic range across the entire image.
Solution Approach 2:
The patent applies local quality by using different gradation curves and weighting amounts for different luminance regions. Each region receives customized processing parameters - for example, preserving chroma in intermediate regions while adjusting highlights and shadows differently. This localized processing maintains natural color and contrast characteristics in each region.
2Illumination intensity
If gradient curve inclination becomes gentle from intermediate to highlight, then dynamic range is extended, but highlight contrast decreases
Solution Approach 1:
The patent employs dynamic weighting amounts that are calculated based on local luminance characteristics and noise levels. The weighting amount is not fixed but dynamically adjusted for each pixel or region, allowing the system to maintain appropriate contrast in highlights while extending dynamic range. This dynamic adaptation prevents the loss of highlight contrast that occurs with static gentle gradation curves.
3Adaptability or versatility
If color tone changes during synthesis, then chroma decreases or hue changes, but image naturalness deteriorates
Solution Approach 1:
The patent applies homogeneity by using the same gradation curve for all color channels (R, G, B) within each luminance region. This ensures that color relationships are preserved and chroma is maintained. By treating all color channels uniformly in each region and avoiding channel-specific processing differences, the system prevents hue shifts and chroma loss that would otherwise occur during synthesis.
Data Source
AI summary
In an image processing apparatus performing synthetic processing on N number of images (where N is an integer of two or larger) being captured from a same photographic scene under mutually different exposure conditions to generate a synthetic image with a higher dynamic range than the N number of images, obtaining the N number of images, and performing low-pass processing on at least one image among the N number of images to generate a low-pass image. Then, a weighting amount in the synthetic processing is decided based on the low-pass image, and the synthetic processing is performed on the N number of images according to the decided weighting amount to generate the synthetic image. Accordingly, a natural synthetic image with fewer changes in contrast, hue, and chroma is generated in a simple configuration when generating the synthetic image.