Contrast enhancement of color images by multiscale nonlinear smoothing

摘要

A method is presented for enhancement of contrast of color images. The dynamic range of luminance is compressed by utilizing multiscale smoothing of the original image by a nonlinear smoothing filter. Each component of RGB is varied with histogram equalization preserving their ratio to the luminance. At first, the logarithm of the luminance is calculated at each pixel and it is processed by the mode filter with triple scales. Obtained three images with different smoothness are next combined linearly and expanded exponentially to produce the luminance with enhanced contrast. At last, the ratio of obtained luminance to its original value is multiplied to each component of RGB and the range of resulted RGB is expanded to [0,255] by the histogram equalization. Nevertheless this method contains nonlinear level transformation, the ratio of each component of RGB to the luminance is preserved.