VGEF: Contrast enhancement of dark images using value gap expansion force and sorted histogram equalization

We propose a novel contrast enhancement method for dark images using the value gap expansion force (VGEF) and the sorted histogram equalization. Based on the observation that the inter-pixel relationship is analogous to the electrostatic force, we define the pixel field spread around each pixel and the pixel mass at each pixel position. We compute the VGEF exerted to a pixel by multiplying the pixel field and the pixel mass. Also, we sort the pixels of the same value into 5 clusters according to their VGEF magnitudes to reduce contour artifacts in the enhanced image. Finally, we obtain output pixel values using the transformation function that equalizes the sorted histogram. Experimental results demonstrate that the proposed algorithm effectively enhances the contrast of dark images, and is applicable to the performance improvement of the saliency detection as well.