Hi guys, I’ve edited my render image using the node editor, and now i would like to export the image with the background set as transparent…
I usually just check che RGBA button and export to png and it works, but now that i’m using nodes it doesnt, i guess it’s because i’ve got to connect the alpha channel of my original render layer to something, but i don’t know…
can someone help me out with this? thanks 
hey, is this that hard?
Render the image as RGBA, then use nodes to tweak stuff, bring up the rendered image again and save the final image (F3) it should still be transparent.
At least it is for me
If for some reason your node tree ends up with an image with no alpha, you should be able to use a Set Alpha node to re-introduce it before the Composite node.
yeah, I tried that but since i used lens distortion nodes and glow nodes, the area where the background was before is not exactly the same as where it is now, and so i get an image like “cropped with scissors” and not with the black background out…
that’s what i get, the letters you can see are totally out of center…
In that case you’ll have to use nodes to build an alpha channel to fit your new imagery, then pipe it into the Set Alpha node. This can be done a number of ways but frequently involves taking the final output image, making it grayscale, filtering it, adding various density masks, etc.
Another option is to take the original Alpha channel (which is an 8-bit grayscale image) and pipe it through nodes that do the same things as your RGB component nodes, so it is being modulated in essentially the same fashion. Whether this can be done or not depends a lot on the nature of your imagery and initial inputs, but it’s usually possible to generate a useable alpha channel.
that actually worked!! thank you so much :DD