Global HDR Tone Mapping with Dual Curves for Histogram Gaps

Solution Overview

Problem

HDR images often have areas of very bright pixels with the rest of the image being quite dark, leading to poor image quality and limited improvement in object recognition due to the histogram gap between dark and bright portions.

Innovation Solution

A method for tone mapping that involves generating a global tone mapping curve using a luminance histogram to identify a gap, applying an auxiliary tone mapping curve for dark pixels and a tail curve for bright pixels, preserving the input dynamic range and enhancing contrast in the dark areas while avoiding overexposure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a general tone mapping transformation is performed on HDR images with bright areas, then the processing is simple and fast, but the image quality and object recognizability show little improvement

Engineering Contradiction:

Improveprocessing speedVSAvoidimage quality

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent divides the tone mapping process into two distinct segments: a first tone mapping curve for dark regions and a second tone mapping curve for bright regions. This segmentation allows each region to be processed with a specialized curve optimized for its characteristics, improving overall image quality while maintaining processing efficiency through automated region classification.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies different tone mapping curves to different regions of the image based on their brightness characteristics. Dark regions receive a first tone mapping curve optimized for enhancing visibility, while bright regions receive a second curve optimized for preserving highlights. This local quality approach ensures each region is processed with the most appropriate transformation.

Inventive Principle:

Principle #3Local quality

2Manufacturing precision

If contrast is increased in dark areas to improve visibility, then object recognizability improves, but the bright areas may become overexposed

Engineering Contradiction:

Improveobject recognizabilityVSAvoidoverexposure

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies different tone mapping curves to different regions of the image based on their brightness characteristics. Dark regions receive a first tone mapping curve optimized for enhancing visibility, while bright regions receive a second curve optimized for preserving highlights. This local quality approach ensures each region is processed with the most appropriate transformation.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent divides the tone mapping process into two distinct segments: a first tone mapping curve for dark regions and a second tone mapping curve for bright regions. This segmentation allows each region to be processed with a specialized curve optimized for its characteristics, improving overall image quality while maintaining processing efficiency through automated region classification.

Inventive Principle:

Principle #1Segmentation

3Device complexity

If a single tone mapping curve is used for the entire image, then the processing is simple, but the histogram gap between dark and bright portions cannot be effectively addressed

Engineering Contradiction:

Improveprocessing complexityVSAvoidhistogram gap handling

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent divides the tone mapping process into two distinct segments: a first tone mapping curve for dark regions and a second tone mapping curve for bright regions. This segmentation allows each region to be processed with a specialized curve optimized for its characteristics, improving overall image quality while maintaining processing efficiency through automated region classification.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent dynamically selects and applies different tone mapping curves based on the local brightness characteristics of each region. The system adapts its processing approach by automatically identifying dark and bright regions and applying the appropriate curve, making the processing complexity adaptive rather than static.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentEP4625309A1Global tone mapping for HDR images with historgram gap

Publication Date: 2025.10.01 INTEL CORP

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AI summary

Techniques for improving image quality of a HDR image by increasing the contrast in the dark portion of the image while preserving the bright parts of the image. The methods preserve the input dynamic range. An image with a luminance histogram gap between a main portion with low brightness and a small portion with high brightness. A first tone mapping curve is determined for the low brightness portion of the image. A second tone mapping curve is determined from a selected point on the first tone mapping curve to a maximum brightness level of the input image. A final tone mapping curve is generated including the first tone mapping curve from a minimum brightness input to the selected point and the second tone mapping curve from the selected point to a maximum brightness level. The method can increase overall image quality and contrast.