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Is it always necessary to add a premultiply node to an image after pulling a key or creating a roto bezier before you merge it on top of another image in Nuke? i guess it never does it automatically for you does it? or is there a premultiply setting in any of the nodes?
deadbeats77,
See my thread: http://www.fxguide.com/forums/showthread.php?t=6697
You get the best results by adding a Premult to the greenscreen side right before the Merge (over) node.
hello fellows
Can anyone explain me the use of premult when u do composting with blue screen. Elsewhere they advice to premult before merge to the background. (nuke)The whole premult issue is a bit confusing for me…( help )
Has anyone knows about any tutorial or good talk about premult issue.from the source, u do blue screen work (primatte, or ibk) work, spill removal with hue correction, and finally before compositing your bluescreen/alpha/bakground, everybody advices to premult with his own alpha before merging it with the background. why?
Why it is not ok to merge it straight without premuted it with his alpha?thx for any aswers….
why? does it look bettter? why black should be better than the green screen itself?
Peter Webb did a nice explanation in our tips section a while back… that can be found here. Another great illustration I found after some quick googling is at Digital Art Form. Also I found a more technical wikipedia entry on the subject. And here is a Toolfarm example in photoshop.
cheers ! i gonna check it
hey again
I have check the links u just sent.
well, it helps a lot. thx again
BUT
i still don t understand the pipeline, why does it look better to multiply the foreground by the alpha. I do understand it is necessary if u use MERGE OVER (nuke. I assumed OVER = ADD in flame structure?) but if u used a BLEND MODE (in nuke. I assumed BLEND in flame= MATTE (in merge/nuke) without premult. it is the same right?I have checkd it with the green screen work in nuke. two methods. first.
1- key primate + hue correction + premult in the merge node (OVER) with the background
2- key primate + hue correction in the merge node (MATTE) with the backgroundthe two result looks the same. no difference.
if i missed something? tell me. i am a bit confused here about the used of premult in this case.
cheers
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