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jeric_synergy
06-09-2014, 09:18 PM
Is there a way to render ONLY the alpha channel, but with all the same AA settings as the full render?

WITH the idea that this would be FASTER.

ernpchan
06-09-2014, 09:33 PM
I've never done just an alpha pass as I render the alpha with my color pass. If the aim is to save on rendering time, wouldn't it be more work to render the extra pass? Exrs would be an option since you can have as many channels you want. The file sizes can get pretty large though.

sukardi
06-09-2014, 09:58 PM
Hi,

Just create a new scene file. Select all your objects. Turn on matte color for all. That should speed up the render a bit. The alpha shouldn't be affected ...

jeric_synergy
06-09-2014, 11:15 PM
Thanks guys.

Sensei
06-10-2014, 01:03 AM
The alpha shouldn't be affected ...

If you have Matte Color turned on, all (most?) Surface Editor settings are ignored.

But in normal situation,
if Transparency is 0% alpha is 100%
if Transparency is 50% alpha is 50%
if Transparency is 100% alpha is 0%

After turning on Matte Color, alpha is always 100%, so Transparency is completely ignored.
If objects cover entire frame, you will get just white image..

Basing on normal RGB color, there is done whole adaptive anti-aliasing. If you don't have color, it can't work properly.

sukardi
06-10-2014, 01:22 AM
If you have Matte Color turned on, all (most?) Surface Editor settings are ignored.

But in normal situation,
if Transparency is 0% alpha is 100%
if Transparency is 50% alpha is 50%
if Transparency is 100% alpha is 0%

After turning on Matte Color, alpha is always 100%, so Transparency is completely ignored.
If objects cover entire frame, you will get just white image..

Basing on normal RGB color, there is done whole adaptive anti-aliasing. If you don't have color, it can't work properly.

Sensei is right of course.

Depends of your scene and what you want to do. If you need the transparency, you can try switching off lights, radiosity etc to speed up the render.

Or if you need both the beauty pass and the alpha, you can always use the save alpha from Render Global>Output panel. It works with all image types...

jeric_synergy
06-10-2014, 01:42 AM
FWIW, I just wanted the alpha as a graphic element, i.e. a 2d-ish motion graphic "look". However, there was already a bunch of surface settings I didn't want to mess with.

Sensei
06-10-2014, 01:50 AM
FWIW, I just wanted the alpha as a graphic element, i.e. a 2d-ish motion graphic "look". However, there was already a bunch of surface settings I didn't want to mess with.

Global Materials (http://globalmaterials.trueart.eu) -> and all settings will be saved with scene, lwo objects will be intact..

Do you saw how I am making 2d cartoon look in GM, overriding the all scene surfaces.. ?
https://www.youtube.com/watch?v=UCCov7Shd7M

BeeVee
06-10-2014, 02:30 AM
If it's *just* the alpha channel of your already-made scene why not just set Save Alpha in your Output settings and not tick Save RGB? Is there something I'm missing?

B

jeric_synergy
06-10-2014, 09:04 AM
I was looking for a FASTER render, and I'd already generated the RGB channels.

It's not hard getting an alpha, it's just hard getting a FASTER alpha.