I am using portable Octave 5.1.0 under Win 10. I mean to write a plot to png with transparent background.
Disclaimer: This question is similar to the two linked below. I opted asking the present different question since I am adding further relevant information (by the same token, question #2 below was not a dupe of #1).
This is what I found:
print(gcf,'-dpngalpha', 'myplot.png');, suggested in Saving a plot in Octave with transparent background, does not work for me.
It is remarkable that I did not find documentation on this option.
This answer has a couple of issues for me: 1) for some unknown reason convert does nothing. 2) The requirement of an external package makes it cumbersome. For instance, I cannot simply send my Octave code to someone else for him to use it.
Option svgconvert is the only official documentation I found.
But it would not apply to a png, e.g.
imwrite seems to have the capability to write with transparency, but I couldn't find a way to transform a plot into and image suitable for imwrite.
(See also Matlab documentation).
Perhaps this is a possible route...
Is there any option available in Octave?
Related:
The imwrite option seems to work. First create the image file img_fname, then create an alpha layer for it.
It would be interesting to know if one could avoid the intermediate non-transparent file.
EDIT: I managed to create the image directly from my plot, instead of requiring the intermediate file.
x = -10:0.1:10;
plot (x, sin (x));
# Print figure directly to image instead of file
im = print(gcf, '-RGBImage');
tcolor = [255 255 255];
alpha(:,:) = 255 * ( 1 - (im(:,:,1) == tcolor(1)) .* (im(:,:,2) == tcolor(2)) .* (im(:,:,3) == tcolor(3)) );
imwrite(im, 'temp.png', 'Alpha', alpha);
Notes:
With a little simple algebra one could add transparency for any number of colors, and any opacity level for each color. Moreover, one could move this into a function.
The multiplication of im and tcolor could be possibly vectorized as well.
Related: