CODEWITHSUNDEEP
matlab
Genevieve
Genevieve

Reputation: 975

Making the "Region of Interest" (ROI) transparent in MATLAB

I've already made a function to cut out the image, and the part I cut out has a black background. I'm trying to make the black part transparent, then I can generate an image sequence that I can create a video with. I've tried converting the image to a double and then replacing the 0 values with NaN: 

J = imread('imgExample.jpg');
J2 = im2double(J);
J2(J2 == 0) = NaN;
imwrite(J2, 'newImg.jpg');

but when I convert it into a video, it doesn't seem to stay. Is there any way to get the black part of the image to be transparent?

http://stackoverflow.com/questions/37959756/how-to-accurately-order-the-clusters-based-on-color-in-matlab

Upvotes: 0

Views: 187

Answers (1)

Tasos Papastylianou
Tasos Papastylianou

Reputation: 22245

From clarifications in comments, you are trying to create a video format that supports alpha transparency using matlab.

In general this seems impossible using matlab alone (at least in matlab 2013 which is the version I use). If you'd like to check if the newest matlab supports videos with alpha transparency, type doc videowriter and have a look at the available formats. If you see anything with transparency options there, take it from there. But the most I see on mine is 24bit RGB videos (i.e. three channels, no transparency).

So matlab does not have the ability to produce native .avi video with alpha transparency.

However, note that this is a very rare video format anyway, and even if you did manage to produce such a video, you would still have to find a suitable viewer which supports playing videos with transparency!

It's therefore important for you to tell us your particular use-case because it may be you're actually trying to do something much simpler (which may or may not be solvable via matlab) (i.e. a case of the XY Problem

E.g. you may be trying to create a video with transparency for the web instead, like here https://developers.google.com/web/updates/2013/07/Alpha-transparency-in-Chrome-video

If this is the case, then I would recommend you attempting the method outlined there; you can create individual .png "frames" with transparency in matlab using the imwrite function. have a look at its documentation, particularly the section about png images and the 'Alpha' property. But beyond that, you'd need an external tool to combine them into a .webm file, since matlab doesn't seem to have a tool like that (at least none that I can see at a glance; there might be a 3rd-party toolkit if you look on the web).

Hope this helps.

Upvotes: 1

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