Semi-Invariant Algorithm for Color to Gray and Back

This paper proposes a reversible algorithm to convert color images to gray images with keeping chroma and spatial resolution. K. Braun and R. L. de Queiroz proposed a color-to-gray mapping algorithm. The method can almost recover the original color, but it had theoretical problems that both chroma and spatial resolution deteriorated. Our algorithm succeeded to solve those problems by devising a color embedding technique. By replacing a subband of a luminance component by quantized high-pass and chrominance signals, semi-invariant algorithm for chroma and spatial resolution can be realized. Experimental results show that the proposed method can recover vivid color images with keeping spatial resolution from textured gray images