Compositing Cinema 4D alphas in Photoshop

swoop
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Post: #1
Hi all,

I need to render my models in Cinema 4D, complete with alpha channels, and work on them in Photoshop.

The problem (or, the problem as I am possibly naively seeing it): how to remove the default black background from Cinema 4D scenes so that only my object is rendered out to file?

If i just plonk an object in Cinema 4D, such as a sphere, and render it out to a photoshop file complete with alpha channels, then I get an image that has the black background included. Obviously not very useful!

I tried adding a Background primitive in C4D, and setting its render tag to "compositing background", but this didn't work.

Any ideas? Am I going about this the right way?

I basically want an image that can be dragged onto another document in photoshop, or another layer, and have its alpha layer intact, so that I get clean, antialiased edges.

thanks for any help
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Posts: 446
Joined: 2002.09
Post: #2
It likely has an alpha channel, you just need to select it - go to the Channels palette in Photoshop, and command-click on the alpha channel. (If there really is no alpha then you've done something wrong in C4D). This will create a selection. Now go back to the layer with the image in it (which would be the background layer if you didn't output a multi-pass image from C4D) and copy-paste into a new layer - delete the background and yer groov'n...
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Member
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Post: #3
Another method would be to use the magic wand tool with the tolerance set to 1 , select the background, Command Shift I to invert selection..then you have the anti-aliased object of your desire.
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Post: #4
Just guessing here, but I thought you could split different channels in your render. In the Render Settings, look for multipass rendering and on he right side you'll find a little triangle button. Click on it and select what you need, then just render.
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Founder
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Post: #5
I really hate to ask the obvious but, you did check the alpha palette in Photoshop right? Although the RGB channel may show your object plus black background, the alpha channel may show the object in white, with background in black. If so, you are good to go. If you know this already, than sorry!

Carlos A. Camacho,
Founder
iDevGames
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Post: #6
Quote:Originally posted by Taxxodium
Just guessing here, but I thought you could split different channels in your render. In the Render Settings, look for multipass rendering and on he right side you'll find a little triangle button. Click on it and select what you need, then just render.

Multipass splits rendering passes (highlights, shadows, reflections, etc.) but AFAIK it doesn't do what he wants - it can split alphas and create multiple alphas for object groups, but the RGBA image is only available on it's own layer.
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Post: #7
Quote:Originally posted by igame3d
Another method would be to use the magic wand tool with the tolerance set to 1 , select the background, Command Shift I to invert selection..then you have the anti-aliased object of your desire.

That can work in some situations, but the alpha will be more accurate, and will always work, whereas the wand can be iffy (imagine trying to select a rendered 8-ball from a black background).
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jamie
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Post: #8
From the Maxon site:

Problem
How can I render the background pure white? (rather than black)

Solution
You can create a background object by selecting Objects=>Scene=>Background, then create a luminant white material and apply it to the Background object.


Does this help?
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swoop
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Post: #9
Thanks all for your replies.

The select alpha channel, then copy and paste into layers certainly does most of what I need, however...

the trick is that the background (whether black or white) is still being rendered in the final image. If I have a solid image, this isn't a problem. But for translucent images such as a glass bubble, the resulting image is very dark, as the (black) background is showing through.

What I'm trying to do is render the object and output it in such a way as to only render the object, without any background coloring at all.

thanks again.
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Post: #10
What you are going to need do...is use some color like cyan or green...just like in the movies..and then remove this color to produce the layers necessary.

There may be something in C4D for this effect.
Usual..in video, you simply apply a key and then the work is done for you while compositing on video.

You can probably do an PS action to take some the pain from doing this.

I remember Ray Dream Studio could produce a grayscale object map and transparency map in the alpha channels......the command clicking that channel would get you the non-transparent object selection with anti-alias and all. Copy and paste would produce a perfect image.

Can C4D produce such a channel from transparency?
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jamie
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Post: #11
C4D does do alpha channels.

If you are rendering your image with the alpha channel already that should be all you need. In the photoshop layers panel check and make sure the channel is there, if it is 'command click' that channel just like igame3d says and copy and paste it, or eliminate the background and you should be good to go.
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Post: #12
I wish could help, but I only know how to do this in FormïZ and 3D Studio! Grin

Anyway, if no-one here has a definitive answer and you can't find the solution from the manual, try asking for help in the forum at CGTalk - they have a forum specifically for Cinema 4D discussions.

Neil Carter
Nether - Mac games and comic art
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swoop
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Post: #13
Thanks to everyone for their help on this.

It turns out that it's a two step process. To get the image set up for compositing, C4D has to render with the "alpha" AND "straight alpha" option, then I have to do the command-click alpha channel, copy and paste layer, delete original layer thing (which I've made into an Action) in Photoshop.

This works quite nicely! I can now cleanly composite lighting effects in my game without them being colorised to the background colour.

thanks!
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jamie
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Post: #14
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swoop
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Post: #15
The trick is with translucency and lighting effects. Normal alpha, with the photoshop munging, works OK for solid objects. But any non-solids or lighting gets trashed with normal alpha, so 'straight alpha' is required.
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