Updating CData of subimage unwantedly resets its colormap

Hi. Below is a class which manages 2 subimages in 1 figure. Both have different colormaps. However, as soon as i try to update the CData of either subimage, its colormap also gets reset. This is not what I want. Instead, I want the colormap to remain the same. Besides redrawing the entire figure, I'm unsure how.

 classdef ImageTest
   properties
       image_1;
       image_2;
    end

    methods
        function obj = ImageTest()

            figure(1);

            subplot(1,2,1);
            obj.image_1 = subimage(rand(5)*100, autumn);

            subplot(1,2,2);
            obj.image_2 = subimage(rand(5)*100, gray);

        end

        function obj = Change(obj)
            set(obj.image_1, 'cdata', rand(5)*100);
            drawnow;
        end
    end
 end

Answer 1

[per isakson]

Matlab uses index-data in combination with a colormap or true color data, which does not depend on a colormap. See:

• Interpreting Indexed and Truecolor Data

That's the best description I find.

.

The first input argument of ind2rgb and ind2rgb8 is supposed to be a matrix of indices (into the colormap), i.e. a matrix of whole numbers. IMO: It's a side effect of calling a mex-function that makes ind2rgb8 work in your case. The error handling doesn't gracefully cover this. Inserting round makes ind2rgb work.

    set(obj.image_1, 'cdata', ind2rgb( round(rand(5)*100), autumn ) );

Answer 2

[Tom]

Found a solution in changing the update code to this:

 set(obj.image_1, 'cdata', ind2rgb8(rand(5)*100, autumn));

Not entirely sure if this is the best way. Also not sure why ind2rgb8 works where ind2rgb fails.