Camera Exposure Control Using Face-Area Luminance Weighting
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Solution Overview
Problem
Conventional camera devices experience noise due to short exposure signals (flickering) in face areas, especially when capturing images with large brightness differences, which affects the visibility of important facial features in surveillance images.
Innovation Solution
A camera device that includes an imaging unit producing long and short exposure signals, a face detection unit, a weighting processing unit to reduce the luminance level of the long exposure signal in detected face areas, and an exposure control unit that performs exposure control using both signals when the luminance level exceeds a predetermined saturation level, thereby suppressing noise and improving visibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If exposure control uses both long exposure signal and short exposure signal to expand dynamic range, then visibility in bright and dark parts is improved, but noise due to short exposure signal (flickering) occurs in face areas
Solution Approach 1:
The patent applies different processing to different regions of the image. Specifically, it detects face areas and applies a weighting process only to the long exposure signal within those detected face regions, while other regions continue to use the conventional dual-exposure synthesis. This localized application of the weighting process suppresses flickering noise in face areas without compromising the dynamic range expansion benefits in other parts of the image.
Solution Approach 2:
The patent segments the image processing into two distinct paths: one for face areas and one for non-face areas. The face detection unit identifies face regions, and then the weighting processing unit selectively applies processing to the long exposure signal only in those segmented face regions. This segmentation allows different processing strategies to be applied to different parts of the image simultaneously.
2Illumination intensity
If exposure time of short exposure signal is significantly shortened to capture bright light sources, then bright parts become clearly visible, but variation of light amount becomes perceptible causing flickering noise
Solution Approach 1:
The patent applies a weighting process to the long exposure signal as a preliminary anti-action to prevent flickering noise. By reducing the luminance level of the long exposure signal in face areas before synthesis, it counteracts the potential for flickering that would occur during dual-exposure synthesis, thereby preventing the noise issue before it manifests in the final image.
Data Source
AI summary
A camera device (1) includes an imaging unit (2) which outputs a long exposure signal and a short exposure signal in one field period. A face detection unit (8) detects a face area from an image captured by the imaging unit (2). The weighting processing unit (12) applies a weighting process to luminance data of the long exposure signal in the detected face area using a weighting constant for reducing the luminance level of the long exposure signal. If the luminance level of the weighting-processed long exposure signal rises to a predetermined saturation level or higher, an exposure control unit (15) performs exposure control using the long exposure signal and the short exposure signal. This can suppress occurrence of a noise due to a short exposure signal (flickering) in the face area, thereby improving visibility in the face area.