premultiplied alpha

[petitlaf]

Hi! Whenever I open a movie file with a premultiplied alpha, the video ends up with a halo in semi-transparent areas. Is there an option in TVP where you can select the color the alpha has been matted with (like you would do in after effects) so that the matte is correctly removed?

Thank you

[petitlaf]

Since asking my question I realized that as long as the video is premultiplied with a black background, TVP will be able to read it correctly. Still, I would like to know if there is a way in TVP to display correctly videos that have been matted with other colors than black.

Thanks

[Peter Wassink]

bottom left in the layerpanel you have anoption to set the BG color.
'none' results in the alpha black you mention.
but if you choose 'color' you can set it to be any color of choice by just clicking in the first square behind it and then colorpick (with the now questionmarked pointer) the desired color.

[petitlaf]

Thank you for your answer. After trying setting the background color like you said, it appears that it only changes the displayed background color, but has no impact on how premultiplied footage is interpreted.

Maybe to make my problem clearer, I have keyed footage that was premultiplied with a neutral gray for previewing purposes. In After Effects, to display the footage correctly, I would open the Interpret footage panel and select the correct color next to "Premultiplied: Matted with color".

I want to know how to do the same thing in TVP.

Thank you.

[malcooning]

Maybe to make my problem clearer, I have keyed footage that was premultiplied with a neutral gray for previewing purposes. In After Effects, to display the footage correctly, I would open the Interpret footage panel and select the correct color next to "Premultiplied: Matted with color".

I want to know how to do the same thing in TVP.

Like you mentioned above, the color for premultiplied mattes in AFX is to allow dealing with footage that has been keyed more poorly. This feature is not available in TVP.

But just to make sure, have you tried importing the footage with different alpha interpretations into TVP (premultimplied/no premultiply)?

matte.jpg (17.41 KiB) Viewed 19381 times

(you get a preview in the import session window, and as you change the alpha settings the result changes in the preview window)

[petitlaf]

From what I understand, premultiplying has nothing to do with poorly keyed footage. You would normally use a premultiplied alpha, as oppose to a straight alpha, for previewing purposes mostly (and also to save on calculations during compositing in some specific instances).

Since asking my question, I talked to a few people, and my problem was that you should normally not use any other color than black for premultiplying (which is why TVP probably doesn't offer that option), because you would risk loosing color information in the semi-transparent edges (some color values could be clipped).

[Fabrice]

I will ask to Hervé our dev team leader. he may help.

[Fabrice]

Here is our answer :
In TVP Animation 9.0, please use non-premultiplied alpha or premultiplied alpha to the black.

More options may be added in the future versions.

[malcooning]

From what I understand, premultiplying has nothing to do with poorly keyed footage. You would normally use a premultiplied alpha, as oppose to a straight alpha, for previewing purposes mostly (and also to save on calculations during compositing in some specific instances).

Since asking my question, I talked to a few people, and my problem was that you should normally not use any other color than black for premultiplying (which is why TVP probably doesn't offer that option), because you would risk loosing color information in the semi-transparent edges (some color values could be clipped).

I didn't say that premultiplying has anything to do with poorly keyed footage. I said that the COLOR feature for premultiplied footage in AFX is there to help with poorly keyed footage, or, as you mentioned yourself, for footage that its alpha has been premultiplied with anything other than black. since AFX is a compositing program it targets problems such as footage of less optimal circumstances. Myself, I find work on TVP always nicer and easier when I have a compositing program teamed up with it. I personally use Digital Fusion. I see the work level in TVP as the Micro, and the compositing software level as the Macro.

[mox]

I already had this problem when exporting set of .tga graphics for programmers and since then, I ALWAYS save in non pre-multiplied alpha... otherwise there are always black outlines.
As far I know, it's not related to TVPaint but to the picture format itself.