Convert a matrix of RGB points to Lab color space.
matrix of row-elements (points with R, G and B values in [0,1]).
matrix of row-elements (points in Lab color space, L should scale in [0,100], and (a,b) in [-110,110].
This transform is based on ITU-R BT 709, using the D65 white point reference. See http://fr.wikipedia.org/wiki/Rec.(underscore)709 for details. also see http://www.easyrgb.com/index.php?X=MATH