Tone Mapping Using Variable Bit-Depth for HDR Image Posterization
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Solution Overview
Problem
Existing tone mapping techniques for high dynamic range (HDR) images often result in posterization and inefficient use of display levels due to assumptions about bit-depth, especially when fewer images are used for generation, leading to distortions and unsuitable results for devices like camera phones.
Innovation Solution
The method involves determining a set of optimal bit-depths at each irradiance range of the scene using exposure bracketed images, followed by irradiance to intermediate display level mapping, which allows for efficient tone mapping that maintains natural contrast and vivid details without distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If existing tone mapping techniques use assumed bit-depth to generate tone mapping curves, then the dynamic range mapping is simplified, but posterization occurs and display levels are inefficiently used
Solution Approach 1:
The patent changes the parameter from fixed assumed bit-depth to variable optimal bit-depth determined through analysis of actual irradiance information distribution in the HDR image. This allows the system to adapt the bit-depth parameter to the specific characteristics of each image, avoiding posterization while maintaining efficient display level utilization.
Solution Approach 2:
The patent performs preliminary analysis of the HDR image to determine the optimal bit-depth and generate an optimized tone mapping curve before actual tone mapping. This preliminary determination of bit-depth based on irradiance information distribution prevents posterization from occurring in the first place, rather than trying to correct it afterward.
2Productivity
If fewer images are used for HDR image generation, then capture time and processing power requirements are reduced, but the assumption-based tone mapping leads to severe posterization and distortion
Solution Approach 1:
The patent determines optimal bit-depth dynamically based on the actual irradiance information present in the available images, rather than using fixed assumptions. This allows the system to achieve high-quality tone mapping even with fewer input images by adapting the bit-depth parameter to match the actual data distribution.
Solution Approach 2:
The system performs self-analysis of its own input images to determine the optimal processing parameters. By analyzing the irradiance information distribution in the captured images themselves, the system automatically determines the appropriate bit-depth without requiring external guidance or assumptions about the input data characteristics.
3Manufacturing precision
If edges are enhanced and colors are boosted to make the tone mapped image appear dramatic, then richer details and vivid colors are achieved, but distortions are introduced in the image
Solution Approach 1:
The patent changes the approach from post-processing enhancement (edge enhancement and color boosting) to parameter optimization during tone mapping. By determining the optimal bit-depth that preserves natural contrast and detail distribution, the system achieves rich details without introducing the distortions associated with aggressive post-processing enhancement techniques.
Data Source
AI summary
A system and method for tone mapping on a high dynamic range (HDR) image of a scene are disclosed. In one embodiment, tone mapping on the HDR image is performed using a set of bit-depths, that corresponds to a plurality of images of the scene, obtained at each unit of an irradiance range of the scene.