An adaptive two-way bandwidth-preserving logarithmic transformation method for image enhancement with uneven illumination

Abstract

An adaptive bidirectional bandwidth-preserving logarithmic transformation method for image enhancement with uneven illumination, which is characterized by including the following steps: Step 1: Input an image with uneven illumination, and perform standardized transformation on the image; Step 2: Calculate the standardized transformation The average brightness AL of the image, and perform a two-way bandwidth-preserving logarithmic transformation on the image according to the value of AL: if AL<127.5, perform a reverse bandwidth-preserving logarithmic transformation first, and then perform a forward bandwidth-preserving logarithmic transformation; otherwise, Then perform forward bandwidth-preserving logarithmic transformation first, and then perform reverse bandwidth-preserving logarithmic transformation; Step 3: Rounding transformation; Step 4: Output image. The characteristics of the invention are: it has the advantages of enhancing the contrast of dark areas and bright areas, the enhancement effect is obvious, the background is well preserved, and there is no halo phenomenon at all, so that the image quality is overall enhanced.

Description

technical field [0001] The invention belongs to the field of digital image processing and relates to a method for enhancing the quality of images with uneven illumination. Background technique [0002] Since human vision is less sensitive to the contrast of images with too high or too low brightness, it is necessary to enhance the contrast of too dark or too bright images (or regions) in order to perceive their details. For images with uneven illumination, there are both high-bright areas and low-dark areas, the general method is not effective, and some halos will appear. [0003] At present, the use of logarithmic methods to enhance image quality has been widely used and researched in various fields of image processing. Among the published patents, such as: a color-preserving defogging method (application number: CN101754032A), a method for reducing speckle noise in synthetic aperture radar images (application number: CN101398487A), an adaptive enhancement method for under...

AI Technical Summary

Problems solved by technology

These methods are only one-way logarithmic transformations, which can only increase the distance between the spectral lines at the low end (dark area) of the grayscale / chromaticity spectrum (or called histogram), thus only improving the low end of the image. (Dark area) contrast, to achieve the purpose of image contrast enhancement

At the same time, they also include the calculation of the subtraction of two images, which may generate negative data, destroy the positive features of the image, and may introduce additional information that does not exist in the source image, destroying fidelity and causing component distortion

[0005] Therefore, the defect of the current logarithmic method for image enhancement is that it does not involve how to improve the contrast of high-end (bright areas) without increasing the information contained in the original image (emphasizing fidelity)

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