保持图像亮度的局部直方图均衡算法

Local Histogram Equalization with Brightness Preservation

现有的局部直方图均衡算法用于图像的对比度增强时,输出图像的亮度与输入图像无关.由于图像增强的很多实际应用需要保持原始图像的亮度,为此提出一种新的局部直方图均衡算法.以子块部分重叠的局部直方图均衡算法(POSHE)为基础,改进其对子块图像的均衡方式:根据亮度均值对子块图像进行递归分解,得到一系列不同灰度范围的子图像,然后对每一个子图像在其相应的灰度范围内进行直方图均衡,最后合并这些子图像的均衡结果.实验结果表明,这种局部直方图均衡新算法既能充分增强图像局部细节,又能保持输入图像的亮度,且亮度的保持程度可由用户进行控制.本文算法使所增强的图像具有更加自然的视觉效果,能更好地满足消费类电子工业对图像对比度增强的应用要求.

As the traditional algorithms for local histogram equalization is used to enhance the contrast of an image,the output brightness is always regardless of the input image. However,this is not the desirable property in many applications where preserving the original brightness is essential, so a new algorithm of local histogram equalization is proposed. Based on the algorithm of partially overlapped sub-block histogram equalization （POSHE） ,we change the way of equalizing sub-block：based on the mean, each sub-block is separated recursively into a series of sub-images with different gray ranges, then the histograms are equalized over their respective gray ranges, and finally the output of the sub-block is composed with the resulting equalized sub-images. The simulation results show that,with the new algorithm,the local details on the image can be enhanced effectively, and the original brightness can also be preserved in the meantime. Besides, scalable degree of brightness preservation may be achieved by choosing the number of recursive separation. The proposed algorithm can enhance the image in a more natural manner and hence,is very useful for many commercial purposes such as consumer electronics where brightness preservation is required.