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We present a new technique for image contrast enhancement via multiscale gradient transformation. In contrast to histogram-based techniques which aim to change the global statistical distribution of pixel intensities, we improve image contrast by modifying the modulus of the gradient image at multiple scales. In computation, a multiscale gradient representation of the image is generated by a wavelet transform (WT). Linear or nonlinear transformation is applied to multiscale gradients. A contrast-enhanced image is obtained from the transformed multiscale gradients by the inverse wavelet transform. Experimental results demonstrate two advantages of the new method: its flexibility to selectively enhance features of different sizes and ability to control noise magnification.>
Lü et al. (2002) studied this question.