Kekre’s fast codebook generation in VQ with various color spaces for colorization of grayscale images

Abstract

Colorization is the term which means to color any gray scale image. In digital image processing terms colorization of grayscale image is nothing but assigning the red, green and blue color component values to each gray value of grayscale image [1, 2]. Colorization is very difficult because it involves assigning three-dimensional (RGB) pixel values to an image which varies along only one dimension (luminance or intensity) [3]. Since different colors may have the same luminance value but vary in hue or saturation, the problem of colorizing grayscale images has no inherently ‛unique’ solution [4]. So user intervention becomes trivial in colorization process to select the ‛better’ match (red, green and blue values) for every grayscale pixel. In [1, 2] authors have proposed some of the simple approaches for colorization of grayscale images, where user intervention is needed only to select the source color image to be used to generate color palette. In [1, 5] different color spaces and pixel window sizes are worked out for coloring grayscale images. All these techniques gives the results subjective to the source color image considered for coloring are very heavy with respect to time complexity. To speed up the process different search algorithms are proposed in [1, 4]. But everywhere the size of source color image is assumed to be equal to or more than to be colored target grayscale image. The paper presents novel colorization technique where this size dependency of source color image and target grayscale image are taken out. The proposed technique generates color palette using vector quantization codebook generation approach. Here Kekre’s fast codebook generation (KFCG) [16, 20, 21] algorithm is used.