Wavelets and subband coding
Signal Processing with Lapped Transforms
Signal Processing with Lapped Transforms
Improved Reversible Mapping from Color to Gray
SIBGRAPI '07 Proceedings of the XX Brazilian Symposium on Computer Graphics and Image Processing
Color to gray and back: color embedding into textured gray images
IEEE Transactions on Image Processing
Accurate reversible color-to-gray mapping algorithm without distortion conditions
Pattern Recognition Letters
Color local complexity estimation based steganographic (CLCES) method
Expert Systems with Applications: An International Journal
Securing color information of an image by concealing the color palette
Journal of Systems and Software
Color recovery of black-and-white halftoned images via categorized color-embedding look-up tables
Digital Signal Processing
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The concept of reversible conversion of color images to gray ones has been recently introduced. Colors are mapped to textures and from the textures the receiver can recover the colors. This was done using the wavelet transform and replacing high-frequency subbands by the down-sampled chrominance planes. The idea is to print a color image with a black and white printer and, then, at a later time, to scan the document and recover colors. In this paper, we propose to use a more robust method, i.e. more resistant to the print-scan noise. We propose to use a largely redundant representation of the chrominance, embedding them into multiple subbands of a general subband transform. In other words, we spread the chrominance onto many subbands. We show theoretically that for minimizing the variance of the error caused by white noise, the chrominance should be replicated into many subbands and not linearly combined. We also demonstrate the method to find the best linear transform to embed the chrominance into the subbands in the more general case of colored noise. We carry a noise analysis to determine bounds to guide us on how many subbands into which to embed the chrominance. Experimental results were carried involving real printing and scanning, as well as using a simulated print-scan path.