Face Detection Auto Exposure for Bright Backgrounds
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Solution Overview
Problem
Standard auto exposure algorithms in digital cameras often overexpose backgrounds when capturing images of subjects against bright backgrounds, leading to unpleasing photos due to the camera's inability to dynamically adjust exposure parameters based on the subject's location within the scene, especially when subjects move or lighting conditions change.
Innovation Solution
A face detection-assisted dynamic auto exposure system that continuously adjusts exposure parameters by tracking the subject's face within the scene, using a face-enclosing rectangle to prioritize subject exposure and adapt to changes in scene lighting, and can switch to standard exposure algorithms when the subject is no longer in the frame, while also handling multiple subjects and allowing user override.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If standard auto exposure algorithms are used to capture images of subjects against bright backgrounds, then the overall scene brightness is optimized, but the subject's face becomes too dark and visually unpleasing
Solution Approach 1:
The patent applies local quality by differentiating exposure treatment between face regions and non-face regions. Face pixels are assigned a weight of 0 (excluded from exposure calculation) while non-face pixels receive a weight of 1/3, creating locally differentiated exposure quality that prioritizes subject illumination over overall scene brightness optimization
Solution Approach 2:
The patent segments the image into face regions and non-face regions using face detection technology. This segmentation allows the exposure algorithm to treat different regions differently, separating the subject (face) from the background and applying distinct exposure weights to each segment
2Productivity
If exposure parameters are locked in statically before image capture, then the camera can take photos quickly, but it cannot adapt to moving subjects or changing lighting conditions
Solution Approach 1:
The patent implements dynamics by continuously updating face detection results and recalculating exposure parameters for each frame in video mode or during photo capture sequence. The exposure parameters are not locked statically but dynamically adjusted based on current face position and scene conditions, enabling adaptation to moving subjects and changing lighting
Solution Approach 2:
The patent employs feedback by using face detection results from each frame to inform exposure parameter calculations for the next frame. The system continuously monitors face position and scene brightness, then adjusts exposure parameters accordingly, creating a closed-loop control system that adapts to changing conditions
3Manufacturing precision
If face detection-assisted auto exposure is used to prioritize subject exposure, then subject illumination is improved, but the algorithm complexity increases
Solution Approach 1:
The patent applies partial action by focusing computational resources only on detecting faces and calculating exposure parameters, rather than performing full image analysis. The exposure calculation uses a simplified formula based on face detection results and scene brightness, avoiding excessive computational complexity while achieving improved subject exposure accuracy
Data Source
AI summary
A system, computer readable medium, and method for dynamically setting a camera's exposure parameters based on face detection are disclosed. When taking a picture or video of a person in front of a bright background, standard exposure algorithms tend to overexpose the background. In one embodiment disclosed herein, a face detection algorithm is run on the current picture or video frame, and the exposure metering region is inset over the detected face. Exposure time, gain, or other exposure parameters may be set based on the pixels within the exposure metering region. In another embodiment, the exposure metering region tracks a moving face according to lag parameters so that the exposure metering region remains substantially over the face. In yet another embodiment, a plurality of faces may be tracked, with the exposure parameters set based on a weighted average of the pixels within the plurality of face-containing exposure metering regions.