An accurate algorithm for color to gray and back

This paper proposes an accurate reversible algorithm to convert full color images to gray images with keeping chroma and spatial resolution. In our previous study, we proposed a reversible color-to-gray algorithm using the two-level Haar wavelet transform with a packet assignment technique. The authors improve the algorithm by devising a color embedding technique. The proposed algorithm distributes color information effectively in the one-level wavelet subbands for preserving chroma and spatial resolution. Experimental results show that the proposed algorithm can improve the recovering accuracy of color images from the textured gray images of the original color images. We also present a practical application to a color-shielded image transmission which can permit a color recovery only to a specific user.