Forum Moderators: Lobo3433 Forum Coordinators: LuxXeon
Blender F.A.Q (Last Updated: 2025 Jan 05 8:38 am)
Which editor or compositor are you using? For example, in Photoshop, when you open an image in a layer, you can import the black and white alpha in the Channels panel, as an alpha source. In the Blender compositor, you would need to set up an Alpha node structure, as illustrated in the documentation here:
https://www.blender.org/manual/composite_nodes/types/converter/set_alpha.html
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LuxXeon posted at 5:59PM Sun, 27 December 2015 - #4245919
Which editor or compositor are you using? For example, in Photoshop, when you open an image in a layer, you can import the black and white alpha in the Channels panel, as an alpha source. In the Blender compositor, you would need to set up an Alpha node structure, as illustrated in the documentation here:
https://www.blender.org/manual/composite_nodes/types/converter/set_alpha.html
I am using Blender's compositor with an image I just rendered in Blender - I don't save it out, I just go straight to the compositor. The separate render layers I set up all show up as options there in a Render Layer node - for example I have a render layer with just some rocks floating in space on it and nothing behind them in the scene; I can select just that render layer and connect it to a Viewer Node and see only those rocks, but if I connect the Alpha output to the Viewer all I get is a solid white image.
In the video I watched they just rendered the image and when they went to the Compositor and connected the Render Layers node's Alpha output to a Viewer node it showed a black and white image - I am not getting that though, so I must have missed a step they did somewhere.
I'd add some screenshots but I actually have another render going right now. If it's still not clear what I am trying to do I will post back later with some images of what I am getting and what I am expecting - I'm still pretty new to Blender and this is my first real foray into the Compositor so I may be using some incorrect terminology in trying to describe this.
DramaKing posted at 6:08PM Sun, 27 December 2015 - #4245920
Turn off the Sky pass under Layer in the Render Layers panel.
I don't see a Sky pass under the render layers. I am rendering with Cycles in Blender 2.75 if that helps.
Under the World options I am using "Background" with a solid color for the surface though - could that be messing it up? Does Blender see the solid color as an object?
In Cycles Properties panel, make sure you have RGBA selected, not RGB, in the Output panel rollout, and be sure the Transparency option is enabled under the Film rollout. Save to PNG. This should allow your alpha layer to save, with the World background transparent.
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LuxXeon posted at 6:00PM Mon, 28 December 2015 - #4245980
In Cycles Properties panel, make sure you have RGBA selected, not RGB, in the Output panel rollout, and be sure the Transparency option is enabled under the Film rollout. Save to PNG. This should allow your alpha layer to save, with the World background transparent.
Thank you so much! Checking the Transparency box solved it. I already had it set to RGBA and PNG but that tricksy Transparency box was the missing piece.
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Hi All,
I am rendering an image in cycles using render layers so I can apply some compositing effects selectively, but every render layer's Alpha is just pure white. Is there a trick to getting the Alpha to work? Do I need to check something special somewhere before rending? I watched a bunch of tutorials on this and no one seems to be doing anything that I can see - the alpha for that layer just automatically comes out as a black and white mask of everything on that layer and I am getting really frustrated with it.
Thanks for any help, Mark