Joint exact histogram specification and nonlinear filter algorithm in wavelet domain

Discrete digital image can achieve exact histogram specification through the strict ordering algorithm in. However, some edge information will be weakened. In this paper, a nonlinear filter algorithm in wavelet domain is proposed, which can solve the problem significantly. Firstly, the proposed approach utilizes wavelet transform to decompose the image and extract the wavelet coefficients. Secondly, exact histogram specification is implemented to low frequency coefficients, and a nonlinear filter algorithm is applied to enhance high frequency wavelet coefficients of different directions. Finally, the image fulfilled with exact histogram specification and enhancement of edge information is obtained through the inverse wavelet transform. Experimental results show that this method is effective for exact histogram specification and enhancing edge information simultaneously.