Invert color in MatrixPlot

Question

How can I invert the grayscale colors when using MatrixPlot? My data is between 0 and 1 and the color scheme when using GrayLevel is white for 1, black for 0. I do not want to simply invert the data, because in that case the legends won't be correct.

MatrixPlot[data, ColorFunction -> GrayLevel]

Answer 1

Use ColorFunction -> (GrayLevel[1 - #] &) with ColorFunctionScaling -> False:

SeedRandom[1]
data = Rescale @ RandomReal[1, {7, 7}];
mp1 = MatrixPlot[data, ColorFunction -> GrayLevel,
   PlotLegends -> Automatic, ColorFunctionScaling -> False, 
   ImageSize -> 300, PlotLabel -> "GrayLevel"];
mp2 = MatrixPlot[data, ColorFunction -> (GrayLevel[1 - #] &),
   PlotLegends -> Automatic, ColorFunctionScaling -> False, 
   ImageSize -> 300, PlotLabel -> "GrayLevel[1-#]&"];
Row[{mp1, mp2}]