Display a scaled version of the matrix a as a color image. The colormap is scaled so that the entries of the matrix occupy the entire colormap. If limits = [lo, hi] are given, then that range is set to the 'clim' of the current axes.
The axis values corresponding to the matrix elements are specified in x and y, either as pairs giving the minimum and maximum values for the respective axes, or as values for each row and column of the matrix a.