Transparent background+setting alpha data

Question

Mohamed 2012-9-30

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/49465-transparent-background-setting-alpha-data

Hi: I have matrix

x=[1 2 3; 0 2 3;0 0 3];

I want to create a png file where the 0s are transparent and the rest of values are half transparent...I tried the following:

x(x<=0)=NaN;
h=imagesc(x);
axis image
set(h,'alphadata',~isnan(x))
set(gca,'color','none');
set(gca, 'visible', 'off') ; 
export_fig asda.png -transparent

(search expor_fig on this site you will find it,saveas acts weird sometimes so I prefer this one).

Problem is how do I make the rest of the ~isnan values half transparent?

if I use alpha(.5) the NaN will get back their colors (cancels the 'alphadata' command)

Thanks,

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Answer 1

Jan 2012-9-30

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/49465-transparent-background-setting-alpha-data#answer_60438

编辑：Jan 2012-9-30

在 MATLAB Online 中打开

x = [1 2 3; 0 2 3;0 0 3];
x = x / max(x(:));  % Scale to [0,1]
A = repmat(0.5, size(x));
A(x == 0) = 1;      % 100% transparent
imwrite(x, 'asda.png', 'Alpha', A);

I do not find in the documentation, if 100% transparency is 1 or 0. So please test thiy.

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Mohamed 2012-9-30

Thanks Jan. However, that reminded me of another issue I was trying to prevent. I am producing hundreds of this kind of matrices. And I want them all to have the same caxis([cmax cmin]). I don't know how to do so with imwrite. That's why I am creating my images from existing figures. I assume the 'alpha' property doesn't work here (what I am doing)? please correct me if I am wrong. Thanks again

Mohamed 2012-9-30