Tone Correction for Face Portions in Images

Solution Overview

Problem

Conventional tone correction methods often deteriorate the contrast between bright and dark portions of human faces in images, leading to unnatural brightness or darkness, especially when the face is significantly different in brightness from the background.

Innovation Solution

A tone correcting apparatus and method that acquires first and second brightness information for block regions and the face portion, respectively, to adjust the image brightness, using a combination of key determination units and a correction gain calculator to apply a correction curve that maintains appropriate tone in the face portion by interpolating gain values based on relative brightness levels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If conventional tone correction is applied to the entire image, then overall brightness is improved, but face portion contrast deteriorates and unnatural brightness occurs

Engineering Contradiction:

Improveoverall brightnessVSAvoidface portion tone accuracy

Core Design Contradiction:

Illumination intensityVSManufacturing precision

Solution Approach 1:

The image is divided into multiple block regions, and tone correction is performed independently for each block based on its local brightness characteristics. This segmentation allows different correction strategies to be applied to different areas, preventing the deterioration of face portion contrast while maintaining overall brightness improvement.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different tone correction characteristics are applied to different block regions based on their local properties. Blocks containing face portions use different correction curves compared to background blocks, ensuring that each region receives appropriate treatment for its specific content and brightness level.

Inventive Principle:

Principle #3Local quality

2Device complexity

If uniform correction curve is applied to all blocks, then processing simplicity is maintained, but local detail loss occurs

Engineering Contradiction:

Improvecorrection processing complexityVSAvoidlocal detail loss

Core Design Contradiction:

Device complexityVSLoss of information

Solution Approach 1:

The image is divided into multiple block regions, and tone correction is performed independently for each block based on its local brightness characteristics. This segmentation allows different correction strategies to be applied to different areas, preventing the deterioration of face portion contrast while maintaining overall brightness improvement.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different tone correction characteristics are applied to different block regions based on their local properties. Blocks containing face portions use different correction curves compared to background blocks, ensuring that each region receives appropriate treatment for its specific content and brightness level.

Inventive Principle:

Principle #3Local quality

3Manufacturing precision

If aggressive brightness correction is applied, then overall contrast enhancement is achieved, but face portion becomes unnaturally bright or dark

Engineering Contradiction:

Improveoverall contrastVSAvoidface portion naturalness

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

Face portions are detected in advance, and their brightness information is acquired before applying tone correction. This preliminary identification allows the correction process to specifically adjust for face portions, preventing them from becoming unnaturally bright or dark while still achieving overall contrast enhancement.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The correction process uses feedback from face portion brightness information to adjust correction characteristics. By monitoring the brightness levels in detected face portions and comparing them against desired ranges, the system can modify correction curves to maintain natural appearance while achieving contrast enhancement.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS8126285B2Tone correcting apparatus providing improved tone correction on image

Publication Date: 2012.02.28 CASIO COMPUTER CO LTD

AI summary

A tone correcting apparatus includes: a first acquiring unit that acquires first brightness information indicating brightness of each of a plurality of block regions that are set to cover an entire area of an image; a face detecting unit that detects a face portion where a human face is positioned in the image; a second acquiring unit that acquires second brightness information indicating brightness of the face portion detected by the face detecting unit; and a correction unit that corrects brightness of the image based on the first brightness information and the second brightness information.