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* @decolor_sparse, ``A sparse linear model for saliency-guided decolorization'', unpublished script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.