Abstract: When applying traditional image enhancement algorithm to low illumination images with uneven illumination distribution,it is easy to produce color distortion and over enhancement of bright areas. To resolve theses problems,an adaptive enhancement algorithm of low illumination image based on maximum difference image was proposed. Firstly,the concept of maximum difference image was proposed,and the initial illumination component was roughly estimated by the maximum difference image. Secondly,the method of alternating guided filtering was proposed,which was used to correct the initial illumination component,so as to realize the accurate estimation of illumination component. Finally,the Gamma transform was designed for image brightness adaptivity,which was able to adaptively adjust the Gamma transform parameters according to the acquired illumination components,thus,the influence of uneven illumination was eliminated while enhancing the image. Experimental results show that the enhanced image effectively eliminates the influence of uneven illumination distribution,the brightness,contrast,detail performance and color fidelity of the image are significantly improved,the average gradient increases by more than one time,and the information entropy increases by more than 14%. Because the proposed algorithm estimates the light component accurately,and the adaptive Gamma transform is optimized for low illumination images,so that the proposed algorithm has very effective enhancement effect for color images under weak light conditions like night.

Key words: low illumination image, image enhancement, maximum difference image, alternating guided filtering, adaptive Gamma transform

摘要： 应用于光照分布不均的低照度图像，传统的图像增强算法会出现色彩失真、亮区过度增强等问题，因此提出一种最大差值图决策的低照度图像自适应增强算法。首先，提出最大差值图的概念，通过最大差值图粗略估计出初始光照分量；然后，提出交替引导滤波的算法，利用交替引导滤波对初始光照分量进行校正，实现光照分量的准确估计；最后，设计了图像亮度自适应的伽马变换，能够根据获取的光照分量自适应调整伽马变换参数，从而在增强图像的同时消除光照不均带来的影响。实验结果表明，增强后的图像有效消除了光照分布不均带来的影响，图像亮度、对比度、细节表现能力和色彩保真度都得到了明显提升，平均梯度提升了1倍以上，信息熵提升了14%以上。由于提出的算法对光照分量估计准确，自适应伽马变换针对低照度图像进行了优化，因此，对于夜间等弱光源条件下的彩色图像具有十分有效的增强效果。

关键词: 低照度图像, 图像增强, 最大差值图像, 交替引导滤波, 自适应伽马变换