Contrast Enhancement for Digital Color Images Using Variants of Histogram Equalization

• Main Authors: Ping-Hsien Lin, 林秉賢
• Other Authors: Hsu-Chun Yen
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/44473391439777502972

碩士 === 國立臺灣大學 === 電機工程學研究所 === 97 === With the prevalence of digital photographing nowadays, more and more consumer electronic devices are installed with photo-shooting functionalities. Most equipment, somehow, is not intended for professional use of photographing, and hence components for this purpose are not delicate enough under economical considerations. This produces pictures that are not fairly acceptable under some extreme shooting conditions, like low-contrasting images, and has to rely on post-processing techniques to improve the quality of these images. In this thesis, we propose two primary methods, Iterative Sub-Histogram Equalization (ISHE) and Statistic-Separate Tri-Histogram Equalization (SSTHE), for contrast enhancement on color images with brightness preservation, and a secondary post-enhancement technique, Gaussian Distributive Filter (GDF), to directly improve contrasts from a micro aspect and reduce brightness quantization of the output histogram from former methods. ISHE generates a high-contrasting image and preserves brightness to some level by iteratively utilizing the BBHE method. SSTHE segments the original histogram into three regions according to the mean and standard deviation of the image brightness, re-ranges spans of each sub-histogram and executes histogram equalization within each scope respectively. GDF locates and disperses over-concentrated values in the histogram with the Gaussian distributive pattern. Since the histogram calculation has already been maturely implemented in hardware, the methods proposed in the thesis could be readily applied on still color images because of their simplicity, as well as low computation requirements make them suitable for consumer electronics.