[Scilab-users] buliding masks for images

[P M]

Dear all,

I build some masks with scilab, that I want to apply later on a set of
images.
I can build these masks a batch process, because I have pixel coordinates
that define the mask coordinates.
Each mask itself will be an image....
For now I use xs2svg and/or xs2png

Now: Is there a way to export images from scilab applying alpha channel?

I ask, because several masks will be layered on top of each
other...together with a mask that is build manually by a user.
To get the final result I - for now - have to make each (mask-) image a bit
transparent, to still see the underlaying image.
Thus I loose the original color of the mask image.

I could probably build an R-G-B-alpha image such as:

img = zeros[imgHeight, imgWidht ,4];

R = img[ : , : ,1];
G = img[ : , : ,2];
B = img[ : , : ,3];
A = img[ : , : ,4];

and than set the right pixel values at the right positions.

However: It seems, that it is not possible to add the alpha channel to an
image when exporting it to a native image file..such as png.

imwrite (IPCV-toolbox) seems to support only 8bit (one-channel) or 24bit
(3-channel) image.

Many thanks,
Philipp
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