Improved knee transfer function and gamma correction based method for contrast and brightness enhancement of satellite image

In this paper, a novel contrast enhancement approach based on knee transfer function and gamma correction using discrete wavelet transform (DWT) has been proposed for quality enhancement of the especially low contrast satellite images. The proposed algorithm computes the knee transfer function using gamma correction scheme in wavelet domain, and then transforms intensity values according to the transfer function. More specifically, discrete wavelet transform is performed first on the input images to get LL, LH, HL and HH frequency components. Intensity transfer functions are adaptively estimated by using the knee transfer function and gamma adjustment function. The conventional knee curve is used to stretch the intensity level, i.e., contrast of the input image. After intensity transformation, the resultant enhanced image is obtained by using inverse DWT. The experimental results demonstrate that the proposed algorithm enhances the overall contrast and visibility of local details better than the existing conventional techniques. The proposed method can efficiently enhance any low-contrast images acquired by a satellite camera, and are also suitable for other different imaging system.