Accurate reversible color-to-gray mapping algorithm without distortion conditions

This paper proposes an accurate reversible algorithm without any distortion conditions such as a print-san process for converting full color images to gray images while preserving the chroma and spatial resolution of the images. In our previous study, we proposed a reversible color-to-gray algorithm using a second-level Haar wavelet transform with a packet assignment technique. We have improved this algorithm by devising a color embedding technique. The proposed algorithm distributes color information effectively in the one-level wavelet subbands for preserving the chroma and spatial resolution. Experimental results show that the proposed algorithm can achieve a higher accuracy of recovering color images from the textured gray images of the original color images. We also present a practical application of the proposed algorithm to a color-hiding image transmission; this application permits color recovery only to a specific user with a key.