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,

Answer 1

[Jan]

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.

[Mohamed]

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]

Actually it does work. so my solution would be similar to yours but. A(x == 0) = 0; and add line alpha(A);

Appreciate it!

Answer 2

[Image Analyst]

Have you seen the official Mathworks documentation: http://www.mathworks.com/help/matlab/ref/imwrite.html#f25-742371

[Mohamed]

Please read above ( first time to post here, don't know if you got notification or something) Thanks