PSNR Comparison of Lung Images Over Histogram Equalization & Several Techniques

Various enhancement schemes are used for enhancing an image which includes gray scale manipulation, filtering and Histogram Equalization (HE). Histogram equalization is one of the well-known image enhancements became a popular technique for contrast enhancement because this method is simple and effective. 

In the latter case, preserving the input brightness of the image is required to avoid the generation of non-existing artifacts in the output image. Although these methods preserve the input brightness on the output image with a significant contrast enhancement, they may produce images which do not look as natural as the input ones. The basic idea of HE method is to re-map the gray levels of an image. 

HE tends to introduce some annoying artifacts and unnatural enhancement. To overcome these drawbacks different brightness preserving techniques are used. Some of them are median filter, wiener filter, linear contrast enhancement technique and un-sharp mask filter. Subjective parameters are visual quality and objective parameters are Peak signal noise ratio (PSNR).

Keywords: Image Enhancement, Histogram Equalization, Median filtering, Wiener Filtering, Linear Contrast Enhancement Techniques, Un-sharp Mask Filtering, Visual Quality, Peak Signal to Noise Ratio.