How to invert contourf(data,[threshold threshold],'k') and modify color

AlphaMask = double(TwoDmatrix < threshold);
whitecover = ones(size(TwoDMatrix, 1), size(TwoDMatrix, 2), 3);
image(whitecover, 'AlphaData', AlphaMask);

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Markus Gschwind 2015-12-20

编辑：Markus Gschwind 2015-12-20

在 MATLAB Online 中打开

Dear Walter,

Thank you!

Is it like this? (I used peaks for illustration).

TwoDMatrix=peaks(30);
threshold = 3;
figure; hold on; 
imagesc(TwoDMatrix); 
[c,h]=contourf(TwoDMatrix),[threshold threshold],'k','Linewidth',2); axis([1 30 1 30])
AlphaMask = double(TwoDMatrix < threshold);
whitecover = ones(size(TwoDMatrix, 1), size(TwoDMatrix, 2), 3);
image(whitecover, 'AlphaData', AlphaMask);

The result looks as follows:

So I would be missing the transparency and also the smoothness of the black line.

I found another way as follows:

figure; hold on; 
g=imagesc(TwoDMatrix); 
[c,h]=contourf(TwoDMatrix,[-Inf threshold],'k','Linewidth',2); axis([1 30 1 30])
allH = allchild(h);
patchValues = cell2mat(get(allH,'UserData'));
patchesToHide = patchValues <= threshold;
set(allH(patchesToHide),'FaceColor','w','FaceAlpha',0.4);

And the result comes with some visible transparency, however all over. It doesn't spear the enclosed clusters within the black lines.

Do you know how to achieve this?

Thanks for your ideas!

Best, markus

Walter Roberson 2015-12-20

在 MATLAB Online 中打开

I should have said

AlphaMask = 0.4 * double(TwoDMatrix < threshold);
whitecover = ones(size(TwoDMatrix, 1), size(TwoDMatrix, 2), 3);
image(whitecover, 'AlphaData', AlphaMask);

after which you can

contour(TwoDMatrix, [threshold threshold], 'k')

Markus Gschwind 2015-12-21