Tone Correction for Backlit Images Using Face Luminance Segmentation
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Solution Overview
Problem
Existing tone correcting methods fail to consistently improve the visibility of figure images photographed against the sun, often resulting in unsatisfactory skin color correction, high memory requirements, and inefficient processing times, especially in extreme backlight conditions.
Innovation Solution
A tone correcting method that calculates a representative luminance value for specific areas of an image and uses a correction parameter based on this value and a predetermined boundary value to adjust pixel values, reducing memory needs and processing time while enhancing image visibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If existing tone correcting methods are applied to figure images photographed against the sun, then the whole image can be corrected to have satisfactory visibility, but the skin color of the figure is not always corrected into a preferable skin color
Solution Approach 1:
The patent divides the image into a figure area and a background area, and applies different correction parameters to each area. The figure area uses correction parameters optimized for skin color representation, while the background area uses parameters optimized for overall visibility, thereby resolving the contradiction between general visibility and specific skin color accuracy
Solution Approach 2:
The patent applies local quality correction by using different correction parameters for different regions of the image. Specifically, the figure area receives correction parameters tailored for skin color accuracy, while the background receives different parameters, allowing each region to be optimized for its specific requirements
2Manufacturing precision
If a face detecting unit is provided to correct skin color, then skin color correction can be achieved, but a large capacity of memory is necessary and processing time becomes long
Solution Approach 1:
The patent extracts only the necessary information (luminance average and standard deviation) from the figure area to calculate correction parameters, rather than processing the entire image or using complex face detection algorithms. This extraction approach reduces memory requirements and processing time while maintaining skin color correction accuracy
Solution Approach 2:
The patent applies partial action by calculating correction parameters based on only the figure area's luminance characteristics rather than the entire image. This partial approach uses fewer computational resources and less memory while still achieving the desired skin color correction effect
3Manufacturing precision
If logarithmic conversion is used to calculate gamma correction value, then gamma correction can be performed, but processing load is increased
Solution Approach 1:
The patent changes the parameter used for correction by calculating correction parameters based on the luminance average and standard deviation of the figure area, avoiding the need for logarithmic conversions. This parameter change approach achieves accurate gamma correction with reduced processing load
Data Source
AI summary
A face detecting unit detects presence/non-presence of a face and its position from an input image or its reduced image. A parameter calculation control unit calculates a correction parameter according to the presence/non-presence of the face. When the face is detected, a face area correction parameter calculating unit calculates a correction parameter having characteristics such that as a representative luminance value is larger, the image becomes darker, and as smaller, the image becomes brighter based on a boundary luminance level. When a face is not detected, a standard correction parameter calculating unit 4 calculates the correction parameter based on image data of the input image or its reduced image regardless of image contents. An image converting unit converts a pixel value of the input image using the obtained correction parameter so as to correct tone.