Colorization of grayscale images and videos using a semiautomatic approach

Colorization is a computer-aided process of adding color to a grayscale image or video. The task of colorizing a grayscale image involves assigning three dimensional (RGB) pixel values to an image which varies along only one dimension (luminance or intensity). Since different colors may have the same luminance value but vary in hue or saturation, mapping between intensity and color is not unique, and colorization is ambiguous in nature, requiring some amount of human interaction or external information. In this paper we propose a semi-automatic process for colorization where the user indicates how each region should be colored by putting the desired color marker in the interior of the region. The algorithm based on the position and color of the markers, segments the image and colors it. In order to colorize videos, few reference frames are chosen manually from a set of automatically generated key frames and colorized using the above marker approach and their chrominance information is then transferred to the other frames in the video using a color transfer technique making use of motion estimation. The colorization results obtained are visually very good. In addition the amount of manual intervention is reduced since the user only has to apply color markers on few selected reference frames and the proposed algorithm colors the entire video sequence.