I have chosen RGBA, PNG output, and Transparent in the Film panel.
I have attached my blend file. Can anyone tell me why it wont give me an alpha channel? I’ve confirmed that there’s no alpha by opening the PNG in photoshop and even after effects.
I checked your blendfile, there is an alpha channel, but your node tree is overwriting it. I. e. at some you inverted the alpha and then added the result to your final composite. If you want the alpha you’ll have to disable compositing in “post-processing” or change your node tree.
Blender actually set the node tree up for me in the 3d tracking view when I clicked on “Setup scene”. Basically it made it so the ground plane renders just a shadow pass. And it works, but when I disable the video track in the background, it mixes the shot incorrectly by removing the alpha somehow. but if i mix it with a video, it has the alpha from the 3d objects, but it makes the background video render out as well. I’m trying to not render the background video, and only use it to get tracking data.
Basically, I’m trying to render only the shadows which have fallen on the plane from an object, and not the actual plane! It set up the nodes for me automatically, but when I remove the video that is attached to it, it wont render the background as an alpha channel, but rather a white background. Ugh,.
That is probably because Cycles doesn’t have a Shadow Only material like Blender Internal, so uses a white plane to capture the shadow and be multiplied with the footage.
I tried so many node combinations and now i got one that works. Check this out(attached) - basically will render alpha as background and not need a video in the back or an image to mix with.