Image Adjustment Apparatus for Non-Uniform Illumination Contrast

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Solution Overview

Problem

Existing image enhancement methods, such as histogram equalization, fail to effectively enhance contrast in visually important areas without over-enhancing brightness or suppressing contrast in areas with few pixels, especially in images with non-uniform illumination.

Innovation Solution

An image adjustment device that derives an illumination component, a reflectance component, and a contrast component, then uses a luminance conversion function to weight and adjust the histogram of a grayscale image, ensuring that visually important areas are enhanced without excessive brightness or contrast enhancement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If histogram equalization is applied to enhance contrast, then the contrast in areas with many pixels is extremely enhanced, but the contrast in visually important areas with few pixels is suppressed

Engineering Contradiction:

Improvecontrast discrimination powerVSAvoidcontrast enhancement accuracy in meaningful areas

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The patent applies local quality by dividing the image into different regions (meaningful areas with few pixels and meaningless areas with many pixels) and applying different contrast enhancement strategies to each region. The histogram equalization is selectively applied only to meaningful areas after identification, while meaningless areas are excluded from the enhancement process, thus preserving their original contrast characteristics.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent segments the image processing task by first identifying meaningful areas versus meaningless areas, then applying histogram equalization only to the meaningful segments. This segmentation approach allows differential treatment of different image regions based on their visual importance and pixel density characteristics.

Inventive Principle:

Principle #1Segmentation

2Object-affected harmful factors

If spatial information is incorporated into histogram equalization to avoid enhancing background noise, then the method becomes ineffective for images with non-uniform illumination components

Engineering Contradiction:

Improvebackground noise enhancementVSAvoideffectiveness in non-uniform illumination images

Core Design Contradiction:

Object-affected harmful factorsVSAdaptability or versatility

Solution Approach 1:

The patent applies preliminary action by first identifying and classifying image areas into meaningful and meaningless regions before applying histogram equalization. This preliminary classification based on pixel density and visual importance allows the method to adapt to different illumination conditions by selectively processing only relevant areas, making it effective for both uniform and non-uniform illumination images.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the parameter of histogram weighting by using pixel density and area classification as weighting factors. Instead of uniform weighting or simple spatial gradient weighting, the method dynamically adjusts the weighting based on whether an area is meaningful or meaningless, enabling effective contrast enhancement across various illumination conditions.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If global contrast component is completely eliminated to obtain reflectance component image, then the brightness is extremely enhanced, but the natural appearance is lost

Engineering Contradiction:

Improvereflectance component extraction accuracyVSAvoidbrightness enhancement level

Core Design Contradiction:

Measurement precisionVSIllumination intensity

Solution Approach 1:

The patent applies partial action by selectively removing the illumination component only from meaningful areas rather than completely eliminating it from the entire image. This partial removal preserves the natural appearance and appropriate brightness levels in meaningless areas while still achieving the desired contrast enhancement in meaningful areas where accurate reflectance extraction is critical.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS12087032B2Image adjustment apparatus, image adjustment method, and program

Publication Date: 2024.09.10 NIPPON TELEGRAPH & TELEPHONE CORP

AI summary

An image adjustment device includes: an illumination component derivation unit that derives an illumination component of a grayscale image; a reflectance component derivation unit that derives a reflectance component image that is a resulting image in which the illumination component is removed from the grayscale image; a contrast component derivation unit that derives a contrast component based on a contrast value between a pixel of the reflectance component image and a peripheral area of the pixel; a histogram derivation unit that derives a luminance histogram of the grayscale image weighted according to the contrast value for each pixel of the contrast component; a conversion function derivation unit that derives a luminance conversion function for converting a luminance such that a luminance histogram of a converted grayscale image in which the grayscale image is converted by the luminance conversion function and a predetermined histogram are matched with or similar to each other; and a luminance conversion unit that generates the converted grayscale image.