PDA

View Full Version : Alpha problem


JacquesD
01-21-2002, 04:03 PM
I'm sure you know about it but I wanted to ask the question just in case.
When saving a image in tga(32bits), if I compose it with another background using the alpha channel there's a kind of dark egde around the rendered image.
Does anyone know why and if there's a way to fix it up?
Thanks in advance.

Dis
01-21-2002, 05:01 PM
that is propably because your alpha-channel is anti-aliased. meaning its mixed up with yes and no information which blends everything with the (probably) black background for a few pixels. there was a plugin released which corrects this. unfortunately i forgot the name, but you can find it at Flay (http://www.flay.com) , just check the news from the few last weeks.

JacquesD
01-21-2002, 07:06 PM
Thanks a lot, exactly what I needed.

Chewey
01-22-2002, 12:12 AM
The problem you are having is referred to as "Blamming". It occurs when you have premultiplied alphas interpreted incorrectly as straight alphas.

For example this happens in AfterFX if you choose the wrong alpha type when first importing the tgas into afx. If you're not getting a message prompt at tga import time to choose between the 2 types of alpha, then you need to set afx's prefs to make sure it provides the prompt.

JacquesD
01-22-2002, 05:26 AM
Thanks for the tip.

CGTalk Moderation
01-13-2006, 01:39 AM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.