基于极大灰度频数抑制结合动态直方图均衡的图像增强算法

Image Enhancement Algorithm Combines Maximum Gray Frequency Restrict with Dynamic Histogram Equalization

现有的直方图均衡技术存在两方面不足:虽然使得增强图像有高的对比度,但是其对比度的提升程度严重依赖于灰度频数分布,这样常常导致容易过度增强高频数灰度级,而压缩低频数灰度级;另外,增强对象缺乏目的性,难以满足感兴趣灰度区域的特殊要求。针对这个问题,该文提出基于极大灰度频数抑制结合动态直方图均衡的图像增强算法。首先通过分析图像直方图的灰度分布情况来分割图像,并根据用户感兴趣灰度范围确定各子层图像的灰度映射范围及频数控制阈值;然后利用各自阈值重新定义子层直方图,并采用直方图均衡算法构造灰度转换函数,将子层灰度映射到指定范围内;最后综合各个子层的增强结果得到最后的增强图像。实验结果表明,该算法既能抑制过度增强的情况,又能对于用户感兴趣的灰度进行控制,能更好地满足用户对图像对比度增强可控的应用要求。

General histogram equalization technology have two drawbacks, it makes the enhanced image have a higher contrast while improvement of contrast dependents on heavily the distribution of gray frequency. So it often leads to enhance high frequency gray level excessively while compresses low frequency gray level. In addition, the enhance process lacks purpose, so it is difficult to meet the special requirements such as to enhance the specified interesting gray level. In order to solve this problem, image enhancement algorithm combines maximum gray frequency restrict with dynamic histogram equalization is proposed in this paper. Firstly, according to analyzing the image histogram and the interested in gray range, the gray range of each sub-level mapping and the frequency control threshold are selected. Then histograms of sub-level after restricting the maximum gray frequency are redefined, by adopting histogram equalization algorithm to construct gray transfer function, mapping sub-level gray to the appointed range. Finally the enhancement result of sub-level is composed. The experimental results demonstrate that this image enhancement algorithm not only could change the situation of the excessive enhancement, but also could control the interest gray level range, and it solves the application requirement that the image contrast enhancement could be controlled.