Fast Hue-Preserving Histogram Equalization Methods for Color Image Contrast Enhancement
Résumé
In this work, we present a generic fast hue-preserving histogram equalization method based on the RGB color space for image contrast enhancement and two instantiation of that generic process. The first method uses R-red, G-green, and B-blue 1D histograms to estimate a RGB 3D histogram to be equalized, whereas the second method uses RG, RB, and GB 2D histograms. The histogram equalization is performed using shift hue-preserving transformations, avoiding unrealistic colors. Our methods have linear time and space complexities with respect to the size of the image and do not need to apply conversions from a color space to another in order to perform the image enhancement. Such design complies with real-time applications requirements. An objective assessment comparing our methods and others is performed using a contrast measure and a color image quality measure, where the quality is established as a weighting of the naturalness and colorfulness indexes. We analyze 300 images from the dataset of the University of Berkeley. Experiments show that the value of the image contrast produced by our methods is in average 50% greater than the original image value, keeping the quality of the produced images close to the original one.