HDR Camera Exposure Control via Image Signal Quantile Analysis
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Solution Overview
Problem
Current image converters struggle to rapidly adapt their sensitivity characteristics to changing brightness distributions in real-time, especially in dynamic scenes, leading to inadequate image contrasts and recognition issues in vehicle driver assistance systems.
Innovation Solution
A method and device that create a frequency distribution of image signal values, determine quantiles, and adjust parameter sets for exposure control, allowing for quick adaptation of sensitivity characteristics to light intensity changes, enabling rapid exposure control and optimal image contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If exposure time is increased to capture darker image areas, then dark areas become visible, but bright areas become overexposed and saturated
Solution Approach 1:
The patent segments the sensitivity characteristic into multiple linear sections with different gradients. The first section (lower brightness range) has a steeper gradient to capture dark areas, while the second section (higher brightness range) has a shallower gradient to prevent saturation in bright areas. This segmentation allows the single image converter to handle the full dynamic range effectively.
Solution Approach 2:
The patent implements dynamic adaptability by enabling rapid switching between different sensitivity characteristics (linear and lin-log) based on scene conditions. The system can quickly adapt to changing brightness distributions within a few consecutive images, making the sensitivity characteristic dynamic rather than fixed.
2Adaptability or versatility
If logarithmic sensitivity characteristic is used to compress intensity differences, then dynamic range handling improves, but cost increases significantly
Solution Approach 1:
The patent uses a lin-log sensitivity characteristic as a cost-effective alternative to true logarithmic sensitivity. The lin-log characteristic achieves similar dynamic range compression effects but can be implemented in standard image converters without requiring expensive specialized sensors, making it an economical solution.
Solution Approach 2:
The patent changes the sensitivity characteristic parameters dynamically by switching between linear and lin-log modes and by adjusting exposure time and gain. This allows the system to adapt to different lighting conditions without requiring multiple specialized sensors, achieving versatility through parameter adjustment rather than hardware complexity.
3Measurement precision
If conventional exposure control methods are used to adapt sensitivity characteristic, then adaptation accuracy improves, but adaptation speed becomes too slow for rapidly changing brightness situations
Solution Approach 1:
The patent uses histogram analysis of the current image to predict and pre-adjust exposure parameters for the next image. By analyzing the frequency distribution of image signal values and determining quantiles, the system can proactively set exposure time and gain to achieve optimal contrast in the subsequent image, rather than reacting too late.
Solution Approach 2:
The patent implements a feedback mechanism where the histogram and quantile information from each image is used to automatically adjust exposure parameters for the next image. This closed-loop control enables rapid adaptation to changing brightness conditions while maintaining precision through quantitative analysis.
4Ease of manufacture
If linear sensitivity characteristic is used, then manufacturing cost is reduced, but image contrast in dark areas deteriorates when brightness differences are large
Solution Approach 1:
The patent makes the sensitivity characteristic dynamic by enabling switching between linear and lin-log modes based on scene conditions. In uniform lighting, the linear mode provides good contrast. In high dynamic range scenes, the system switches to lin-log mode to maintain contrast in both dark and bright areas, achieving adaptability with a standard image converter.
Data Source
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AI summary
The invention relates to a method for matching the sensitivity characteristic of an image converter (100) to the light-intensity distribution of an optical image which is projected onto the photosensitive surface (11_1) of the image converter. The method has steps for creation (S1) of a frequency distribution of the image signal values in the optical image converted by the image converter, for determination (S2) of one or more quantiles of the frequency distribution (300) of the image signal values, and for creation (S8) of a matched parameter set of setting values of the image converter on the basis of the specific quantile or quantiles of the frequency distribution.