A new wavelet-based method for contrast/edge enhancement

Contrast enhancement is usually achieved by histogram equalizing image pixel gray-levels in the spatial domain to redistribute them uniformly. Meanwhile, edge enhancement attempts to emphasize the fine details in the original image. But in the spatial domain it is hard to selectively enhance details at different scales. Moreover, in the spatial domain, applying contrast and edge enhancement techniques in different orders may yield different enhancement results. To overcome the above spatial domain enhancement issues, a new wavelet-based image enhancement method is proposed. The proposed method histogram-equalizes the approximation-coefficients. At the same time, it high-boost filters the detail-coefficients at selected resolution levels separately. The experiments show that utilizing the proposed method can achieve robust contrast and edge enhancement. Moreover, the computation cost in the wavelet domain is less than that in the spatial domain. This is especially true when considering that currently most images are already wavelet-compressed (the current JPEG 2000 standard is a wavelet based scheme).