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tiffs with alpha - premultiply doesn't work as it should?

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Andy Winter
tiffs with alpha - premultiply doesn't work as it should?
on Feb 16, 2015 at 5:43:37 pm

dear all!

i am once again trying to master in davinci resolve 11 after cc-work :)

but:
i have the movie-titles as tiffs with alpha channel. when i import them in davinci,
there are easy to see small steps in the outline of the font. when i do change the
alpha mode via clip-properties from straight to premultiplied, nothing changes at all!

when i do import the same tiff in after effects, and render a movie in prores4444 with
alpha premultiplied, then import it again in davinci and set the alpha channel accordingly,
the steps are gone and it looks as it should.

there must be an easier solution! how do you fellow colorists, handle this? am i the only one?
shouldn't there be a visible change when i change the alpha from straight to premulti?

i am no graphics expert, so any tipp welcome!

thanks in advance,

andy


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Andy Winter
Re: tiffs with alpha - premultiply doesn't work as it should?
on Feb 17, 2015 at 4:02:59 pm

hmmm... noone? can someone confirm the issue?


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Joseph Owens
Re: tiffs with alpha - premultiply doesn't work as it should?
on Feb 17, 2015 at 7:22:02 pm

[Andy Winter] "trying to master in davinci resolve 11 after cc-work :)"

Didn't know one could do closed caption work in Resolve.

Do you see the stepping in preview or have you test-rendered?

jPo

"I always pass on free advice -- its never of any use to me" Oscar Wilde.


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Andy Winter
Re: tiffs with alpha - premultiply doesn't work as it should?
on Feb 17, 2015 at 10:01:43 pm

:)

it is in preview and its in renders. it also happens when i change the scaling of
a tif with alpha... small steps, dirty outlines. doesn't happen in after effects...


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Andy Winter
Re: tiffs with alpha - premultiply doesn't work as it should?
on Feb 19, 2015 at 3:38:59 pm

can anybody plz try this and confirm?

if it is a bug, it needs a fix!


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Sascha Haber
Re: tiffs with alpha - premultiply doesn't work as it should?
on Feb 19, 2015 at 5:23:13 pm

Upload your files, we will check

Resolve 11.2 - Smoke 2015 EXT1SP2 - Sapphire 8
Colorist / VFX Guru / Aerial footage nerd
http://vimeo.com/saschahaber
https://dk.linkedin.com/in/saschahaber


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Andy Winter
Re: tiffs with alpha - premultiply doesn't work as it should?
on Feb 19, 2015 at 9:52:22 pm

try it with this random tif with alpha:
http://84.112.19.19:5000/fbsharing/aVMlJUnl

and put it in a hd project. put it above pure white or a bright screen.
make it fit your timeline (via image sizing or manually), you will be
able to see small steps and dirty outlines. or won't you?

then try it again in a different software and see if it looks the same! plz!


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Sascha Haber
Re: tiffs with alpha - premultiply doesn't work as it should?
on Feb 23, 2015 at 2:21:09 pm

So, this seem to be more than a small problem....
First, there IS a discussion on the BMD Forum about it, so they seem to know (nudge, nudge)
http://forum.blackmagicdesign.com/viewtopic.php?f=3&t=17449
I did try the premultiply setting and all others but no, not the effect i was getting from Smoke...
Here , when I load in your image and set Smoke to expect an unpremultiplied image i get the same result


But when I set it to premultiply Smoke does the job , takes the separated alpha and it leads to good results.



So to get the job done you need to ask your graphic department to deliver a separate alpha and render out or make premultiply in Photoshop.
For this I faked it by overpainting your text with color.



And then in Resolve you load in that new premultiplied Foreground and your Alpha as a mask , put in on a track, add an alpha node and use the Alpha image to cut it out.



Like back in the days on Quantel Paint box ;)
Maybe it's worth logging this as a bug as of this moment i need to do this clunky workaround to get a decent result.

Resolve 11.2 - Smoke 2015 EXT1SP2 - Sapphire 8
Colorist / VFX Guru / Aerial footage nerd
http://vimeo.com/saschahaber
https://dk.linkedin.com/in/saschahaber


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Andy Winter
Re: tiffs with alpha - premultiply doesn't work as it should?
on Feb 23, 2015 at 8:46:58 pm

thank you very much for testing sascha!

the workaround gets of course into problems, when you try to animate a title in davinci!
(eg. animating a movie title!)

so i would stick to the term BUG :)


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Sascha Haber
Re: tiffs with alpha - premultiply doesn't work as it should?
on Feb 24, 2015 at 8:48:41 pm

I would stick to the term "missing and much wanted feature "

But in the long run, I want to click on a clip in the edit page and Fusion 8 opens and i CAN do proper compositing.
Like in Nuke Studio....that is where the bar is right now.

Resolve 11.2 - Smoke 2015 EXT1SP2 - Sapphire 8
Colorist / VFX Guru / Aerial footage nerd
http://vimeo.com/saschahaber
https://dk.linkedin.com/in/saschahaber


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