Dynamic Range Estimation for Auto-Exposure Clipping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Digital images captured by CMOS and solid state image sensors face limitations in dynamic range due to pixel saturation, analog-to-digital conversion, exposure settings, and bit width processing, leading to clipping of bright areas and loss of information, especially in scenes with rapid luminance changes.
Innovation Solution
The method involves modifying gain stages in the image processing pipeline to process pixel luminance values beyond the typical dynamic range, using intentional underexposure during pre-image capture to prevent clipping, and applying additional gains to restore signals, allowing the auto-exposure module to access non-clipped luminance information for accurate exposure settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If higher gains and longer exposures are used, then the brightest areas of the scene are exposed, but brightness clipping and loss of detail occur in the brightest areas
Solution Approach 1:
The patent applies preliminary action by capturing a pre-image at a first exposure setting before the actual image capture. This pre-image allows the system to estimate scene luminance distribution and determine optimal exposure settings in advance, preventing clipping while maintaining detail in brightest areas during the actual capture operation.
Solution Approach 2:
The patent implements dynamics by adapting the exposure setting dynamically based on scene luminance estimation. The system adjusts the exposure setting from a first exposure setting during pre-image capture to a second exposure setting during actual capture, optimizing the balance between brightness and detail preservation based on real-time scene analysis.
2Loss of information
If lower gains and shorter exposures are used, then clipping is prevented, but the image becomes darker and noisier
Solution Approach 1:
The system performs preliminary image capture at a first exposure setting to gather luminance information, then uses this information to determine an optimized second exposure setting for actual capture. This preliminary action enables the system to prevent clipping while maintaining adequate brightness by selecting the optimal exposure setting based on scene characteristics.
Solution Approach 2:
The patent implements feedback by using the pre-image luminance information to adjust the exposure setting for actual image capture. The system analyzes the luminance distribution from the pre-image and feeds this information back to determine the optimal exposure setting, creating a closed-loop system that optimizes both brightness and detail preservation.
3Loss of information
If the exposure setting is decreased to prevent clipping in brightest areas, then detail is preserved, but the main subject becomes underexposed
Solution Approach 1:
The system captures a pre-image at a first exposure setting that may result in some clipping, then uses luminance estimation from this pre-image to determine an optimized second exposure setting. This preliminary action provides the data needed to balance the exposure settings, ensuring both brightest areas and main subjects receive appropriate exposure while preserving detail.
Solution Approach 2:
The patent applies parameter changes by adjusting the exposure setting from a first exposure setting during pre-image capture to a second exposure setting during actual capture. This parameter adjustment is based on luminance estimation and ensures optimal balance between preventing clipping and maintaining subject exposure, adapting the exposure parameter to scene-specific requirements.
4Adaptability or versatility
If rapid luminance changes occur in the scene, then the camera can capture dynamic scenes, but the image saturates and becomes clipped
Solution Approach 1:
The system captures a pre-image before the actual image capture to estimate scene luminance distribution. This preliminary action provides advance information about the scene's brightness characteristics, enabling the system to select an optimal exposure setting that prevents saturation and clipping even when rapid luminance changes occur during the actual capture.
Solution Approach 2:
The patent applies the skipping principle by using a rapid pre-image capture to quickly estimate luminance information before the actual capture. This allows the system to quickly determine the optimal exposure setting and adjust it in time to prevent clipping during rapid luminance changes, effectively skipping the trial-and-error exposure adjustment process.
Data Source
AI summary
A method, apparatus, and system for dynamic range estimation of imaged scenes for automatic exposure control. For a given exposure time setting, certain areas of a scene may be brighter than what a camera can capture. In cameras, including those experiencing substantial lens vignetting, a gain stage may be used to extend dynamic range and extract auto-exposure data from the extended dynamic range. Alternatively, dynamic range can be extended using pre-capture image information taken under reduced exposure conditions.