Demo code of the implementation of the following papers: * @rgb2gray, Matlab build in function * @decolor_linear2006, ``Decolorize: Fast, contrast enhancing, color to grayscale conversion.'' Patter Recognition 40, 2007 * @decolor_nonlinear2009, ``Robust color-to-gray via nonlinear global mapping'' Siggraph Asia, 2009 * @decolor_sparse, ``A sparse linear model for saliency-guided decolorization'', unpublished script To see the result, execute ``demo.m'' in Matlab.