How can I overlay pseudocolor images with different colormaps?

Question

Laurent G 2016-3-9

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回答： Isaac Breinyn 2019-6-16

Using Matlab R2015b with OpenGL rendering, I am trying to superimpose two pseudocolor images associated with different colormaps. Both images correspond to matrices displayed using imagesc. The commands are the following:

% Examples of matrices x=linspace(-7,7,200);y=x;[X,Y]=meshgrid(x,y);Z1=(X.^2+Y.^2).*exp(-(X.^2+Y.^2)/3^2);Z2=exp(-X.^2-Y.^2);

% New figure

hf=figure;

% Background image

h1 = axes;colormap(h1,'parula');p1=imagesc(x,y,Z1);set(h1,'ydir','normal');

% Foreground image

h2=axes;set(h2,'color','none','visible','off');colormap(h2,'jet');p2=imagesc(x,y,Z2,'alphadata',Z2>1e-2);set(h2,'ydir','normal');linkaxes([h1 h2])

I would like to display only the central part of the (Gaussian) matrix Z2, hence the transparency applied to its wings (with values < 1e-2). Doing so, the foreground image indeed gets paler, yet remains opaque to the background image. Actually, it remains opaque to the latter even by setting full transparency, i.e., set(p2,'alphadata',0)!

Consequently, I wonder whether it is possible at all to overlay pseudocolor images.

Thank you for your help.

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Answer 1

Mike Garrity 2016-3-9

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编辑：Mike Garrity 2016-3-9

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You actually have it exactly right, but the second call to imagesc reset the axes h2. This set the Visible property back to on. Just move this line:

set(h2,'color','none','visible','off');

Down to where you're doing this:

set(h2,'ydir','normal');

As long as an axes hold state is off, a plotting command will reset its properties. This means that changing properties on the axes before the plotting command doesn't work very well.

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Answer 2

Isaac Breinyn 2019-6-16

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在 MATLAB Online 中打开

For anyone else who remained confused for a moment, one must also move the line

colormap(h2, 'jet');

after imagesc, so that the working example is:

    % Examples of matrices 
    x=linspace(-7,7,200);y=x;
    [X,Y]=meshgrid(x,y);
    Z1=(X.^2+Y.^2).*exp(-(X.^2+Y.^2)/3^2);
    Z2=exp(-X.^2-Y.^2);
    % New figure
    hf=figure;
    % Background image
    h1 = axes;colormap(h1,'parula');
    p1=imagesc(x,y,Z1);
    set(h1,'ydir','normal');
    % Foreground image
    h2=axes;
    p2=imagesc(x,y,Z2,'alphadata',Z2>1e-2);
    set(h2,'color','none','visible','off')
    colormap(h2,'jet');
    set(h2,'ydir','normal');
    linkaxes([h1 h2])