Automatic Tone Mapping Curve Generation via Histogram Analysis
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Solution Overview
Problem
Conventional tone mapping techniques require user input or use symmetrical curves, leading to visually unappealing images in certain scenes or light levels, as they fail to independently adjust low and high brightness ranges effectively.
Innovation Solution
An automatic tone mapping algorithm that utilizes image histogram metadata to dynamically adjust tone mapping curves, allowing independent boosting of low and high brightness ranges, and updates the tone curve gradually with changing exposure parameters to maintain visual appeal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional symmetrical tone curves are used to map image characteristics, then the tone mapping process is simple and consistent, but the visual appeal of images in certain scenes or light levels deteriorates because low and high brightness ranges cannot be independently adjusted
Solution Approach 1:
The patent divides the tone mapping process into separate handling of low brightness ranges and high brightness ranges. By computing low endpoint and high endpoint values from the image histogram and independently adjusting slopes at these endpoints, the system can optimize each brightness range separately rather than using a single symmetrical curve, thereby improving image visual appeal while maintaining computational efficiency.
Solution Approach 2:
The patent applies different tone mapping parameters to different regions of the brightness histogram. By calculating endpoint slopes (lowEndpointSlope and highEndpointSlope) based on local histogram characteristics at the low and high ends, the system tailors the tone curve to local image characteristics rather than applying a uniform transformation, which enhances visual appeal in specific brightness ranges.
2Manufacturing precision
If user input is required to select appropriate tone curves for different scenes, then tone curve selection can be optimized for specific conditions, but the ease of operation deteriorates due to the need for user intervention
Solution Approach 1:
The patent implements an automatic tone mapping system that computes endpoint slopes and generates tone curves without user input. By analyzing the image histogram to determine low and high endpoint values and calculating appropriate slopes based on histogram distribution, the system performs self-service tone optimization adapted to each specific image, eliminating the need for manual user selection while maintaining scene-specific optimization.
Solution Approach 2:
The patent dynamically changes tone mapping parameters (endpoint slopes, endpoint values) based on image-specific histogram characteristics. Rather than using fixed user-selected curves, the system computes parameters such as lowEndpointSlope, highEndpointSlope, lowEndpoint, and highEndpoint from the actual image data, allowing automatic adaptation to different scenes and lighting conditions.
3Speed
If tone curves are updated rapidly to match changing image histograms, then the tone mapping responds quickly to scene changes, but visual stability deteriorates due to jarring transitions between frames
Solution Approach 1:
The patent implements dynamic tone curve adjustment where endpoint slopes and values are recomputed for each frame based on the current histogram. The system adapts tone mapping parameters in real-time to changing scene conditions while using damping factors to control the rate of change, creating a dynamic system that responds to scene changes while maintaining visual stability through controlled transition rates.
Solution Approach 2:
The patent applies damping factors to the tone curve update process to prevent jarring transitions. By cushioning the changes in endpoint slopes and values between frames, the system smooths out rapid fluctuations while still allowing adaptation to genuine scene changes, thereby maintaining visual stability without completely suppressing responsive behavior.
Data Source
AI summary
An apparatus, method, computer useable medium, and processor programmed to automatically generate tone mapping curves in a digital camera based on image metadata are described. Rather than having a static tone mapping curve for all images, the curve can be varied automatically based on, e.g., the brightness histogram of the image. In one embodiment, a certain percentage of the least bright pixels and a certain percentage of the brightest pixels can be disregarded, while the remaining pixels can be linearly stretched to encompass the original range of brightness values. Based on the distribution of the resultant stretched brightness histogram, slopes for the low end (S0) and high end (S1) of the tone mapping curve can be independently determined, and the tone mapping curve can be automatically generated. The improved, automatically generated tone mapping curve may be able to lift shadows more aggressively and/or increase the dynamic range of the image.