Improved adaptive color embedding and recovery using DC level shifting

Several color-to-gray image mapping (CGIM) methods were proposed so far to restore a color image from its corresponding printed grayscale image. They are based on embedding chrominance values into high-frequency subbands of the luminance signal. In the conventional methods, textures often become noticeable in the chrominance-embedded gray image since subsampled chrominance values are embedded directly. As a result, qualities of the chrominance-embedded grayscale images are degraded especially for images with rich textures. In this paper, we propose an improved CGIM method using DC level shifting and directional transform. In the experimental results, our method greatly improves the qualities of both the chrominance-embedded grayscale and the restored color images in comparison with conventional methods.