An improved technique for image contrast enhancement using wavelet transforms

Image contrast is an integral part of an image. A good contrast can significantly enhance features of a picture which may earlier be hard to recognize. Underwater and medical images need to have image contrast enhancement most of the times. We have proposed here some new methods which include combination of Wavelet Transforms (both Discrete and Stationary) and Contrast Limited Adaptive Histogram Equalization (CLAHE). The low frequency as well as the high frequency components from both Stationary Wavelet Transform (SWT) and Discrete Wavelet Transform (DWT) are combined and then CLAHE is applied on the low frequency part only. Then the image is reconstructed using Inverse Wavelet Transforms. Extensive experiments on a number of images, calculation of parameters like Local Entropy Increment (LEI), Peak Signal to Noise Ratio (PSNR), etc. from these experiments show that this method is better than existing methods both quantitatively and qualitatively.