The only difference with the situation there, is that I don’t want any background: I just want the object (the cube) + its shadow, and apart from that only transparency. I want to add the background later, manually.
I can follow just fine, until the last step where the answer says
you now have a shadow to multiply over your backdrop and layer 1 to composite into backdrop
Can someone help me to achieve what I want (object + shadow only)
The white parts do not matter if you combine images with “multiply”.
If you read colors as numerical values, white equals 1. So whatever background color X you multiply with white, it will always stay unchanged, as X * 1 = X.
The darker colored (shadow) parts on the other hand represent values < 1, so any background color multiplied with that will become darker.
How can I have just the cube and the shadow in a correct way, and all else transparent?
Is there a way to tell blender to turn white (RGB 255, 255, 255) into transparent?
You’re not doing the compositing correctly in post #3. You…
a) “Multiply” the shadow layer with the background and then
b) “Alpha over” the layer with the shadow casting object on top of that…
Thereby the background receives the shadow and the shadow caster is sitting “on top”.
Yes, I know that that is the original idea, but in my case I have no background. I want no background, I want the final render to be transparent. So I have nothing to multiply the shadows with… I think my post #4 solves it, but I’m a blender noob and maybe it has some drawbacks that I don’t realize yet…