Zone-Based Tone Mapping for HDR Image Exposure Estimation

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Solution Overview

Problem

Current tone mapping methods for high dynamic range (HDR) images on low dynamic range (LDR) displays fail to effectively maintain both local contrast and relative brightness, prioritizing the former over the latter, which is crucial for artistic representation.

Innovation Solution

A zone-based tone mapping method that divides HDR images into regions, estimates exposure for each region by determining anchor points to map most pixels to mid-gray, and adjusts these points to preserve overall brightness, allowing for user interaction to refine the exposure values.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If local tone mapping methods are used to adapt parameters to local image characteristics, then local contrast is improved, but relative brightness perception deteriorates

Engineering Contradiction:

Improvelocal contrastVSAvoidrelative brightness

Core Design Contradiction:

Manufacturing precisionVSLoss of information

Solution Approach 1:

The image is divided into multiple regions with different exposure characteristics. Each region is processed independently with its own exposure estimation and tone mapping parameters, allowing local contrast optimization while tracking regional brightness changes to maintain overall relative brightness perception

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The method estimates exposure for each region and uses this information to adjust tone mapping parameters. The exposure estimation acts as feedback that guides the tone mapping process to preserve both local contrast and relative brightness perception across different image regions

Inventive Principle:

Principle #23Feedback

2Loss of information

If manual region-based exposure adjustment is used, then perceptual brightness is maintained, but processing time increases

Engineering Contradiction:

Improveperceptual brightnessVSAvoidprocessing time

Core Design Contradiction:

Loss of informationVSLoss of time

Solution Approach 1:

The system automatically estimates exposure for each region and performs tone mapping without requiring manual user input. The algorithm self-adjusts exposure parameters based on image statistics, eliminating the time-consuming manual exposure adjustment process while maintaining perceptual brightness

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The manual mechanical process of adjusting exposure for each region is replaced by an automated computational algorithm. The system uses image statistics and exposure estimation to automatically determine tone mapping parameters, substituting manual operation with automated image processing

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS8346009B2Automatic exposure estimation for HDR images based on image statistics

Publication Date: 2013.01.01 INTERDIGITAL MADISON PATENT HLDG

AI summary

A method for tone mapping high dynamic range images for display on low dynamic range displays wherein high dynamic range images are first accessed. The high dynamic range images are divided the into different regions such that each region is represented by a matrix, where each element of the matrix is a weight or probability of a pixel value. An exposure of each region is determined or calculated by estimating an anchor point in each region such that most pixels in each region are mapped to mid grey and the anchor points are adjusted to a key of the images to preserve overall brightness. The regions are then placed or mapped to zones and exposure values are applied to the regions responsive to the weight or probability. The regions are fused together to obtain a final tone mapped image.