importing quicktimes with alphas

[Grinner Hester]

welcome to 1995 technology.
You’re best off exporting the clip you are compositing your graphics over as a reference file and doing the final render in AE. I know this can’t always be planned and the idea is to have graphics done, in a bin and waiting but other than what ya already did, thats your work around.
Sometimes you can change the color of your comp’s background to make it less bogus. lol
I have to admit to doing that a time or two.

[Steve Pomerantz]

Rather than creating quicktimes out of AE, render your graphics out as PNG sequences with alpha. This allows the Avid to use a pre-multiplied alpha channel, rather than a flat one. Your glows and lens flares will key much more cleanly.

Hope this helps.

Steve Pomerantz
Digital Ranch Productions
Sherman Oaks, CA

[Dan Jacobsen]

thanks guys.

i tried the png seq and it was good but not perfect. the lens flares at the start went on in a more or less additive manner but the ones at the end brought in a small ammount of black.

much better than what i had though!

should i get perfect results or is this as good as it gets. it’s fine for this job but i’m interested for future reference.

out of interest i tried tiff and tga seqs. the avid brought in the alphas without converting to rt mattes but they didn’t work half as well as the png seq. any reason for this?

as i say i’m just interested for future reference.

cheers

[Erik Pontius]

You can see the state of your alpha in AE by clicking on the “show only alpha” button (a white button) in the comp window. If the screen is completely white, your alpha when imported into Avid will lack an transparency.
Some effects, such as AE’s Lens Flare effect, will need to be “unmultiplied” to create a proper alpha channel.
Walker Effects has a “Premultiply” plugin that will do the trick by choosing the “unmultiply” option (the plugin is included on the companion CD of the Meyer’s “Creating Motion Graphics with After Effects” books).
There is also a free “Unmult” plugin available for download at Red Giant Software:
https://www.redgiantsoftware.com/unmult.html

I’d also recommend exporting “straight” alphas from AE instead of the default “premultiplied” option in the render queue output module.

Erik

[Dan Jacobsen]

also they seem heavily compressed. strangely i can’t see a difference (but it is just text and glows on grey and white) but they png seq are about 7MB as apposed to movs and tga seq that are 200MB.

how come?

cheers

[Grinner Hester]

avid just likes png files the most. Handles soft drop shadows and such much better but as you are seeing they are many years behind the competition with this. Avid seems to have never assumed we make finished shows for a living. They still like to have ya hit multiple applications to git r dun.

[Dan Jacobsen]

thanks.

i’m using sapphire lens flare which works on alpha as well, i don’t think there’s any options for this.

i’m happy that the alpha is correct as i can put the comp or indeed a generated quicktime over other stuff in AE and it keys over perfectly.

i don’t understand what you mean about straight alphas. surely that would go into the avid as a seperate clip and then act as a matte when combined with the main gfx. is that what you mean or am i missing the point?

cheers mate

[Erik Pontius]

Premultiplied and Straight are different ways of generating the alpha channel. Problem with Premultiplied alpha is that it includes the background in with the RGB channels and then information about how to remove that background. Problem comes when you have subtle semi-transparent areas like drop shadows, the background color is not always completely removed, causing obvious quality problems. Try changing your background color in AE to a gawdawful pink color (composition, background color), then export and import into Avid, you’ll probably notice that some of the nasty pink color wasn’t removed from some areas.
Straight includes alpha information on a separate channel and can be removed cleanly since it doesn’t include the background mixed in with the rest of the image.
When you are finished with your comp and choose to add it to the render queue, under your output module settings there are options for Channels where you would choose RGB + Alpha and a pull down for Color, in it are two options: the default “Premultiplied (matted)” and “Straight (unmatted)”. Choose “Straight (unmatted)” from the pull down and render out your file. Import it into Avid and look at the results.

There is also a video tutorial here at the COW on it:
https://library.creativecow.net/articles/rabinowitz_aharon/straight_vs_premult.php

Erik

[Gary Oberbrunner]

PNG is a lossless compression format. You can go from TIFF (or uncompressed QT) -> PNG and back and it’ll be bit-for-bit identical with the original. But as you can see it does a good job keeping the size down.

— Gary

[Dan Jacobsen]

that’s great thankyou.

i didn’t know the correct terminology. premultiplied sounds like using a matte and a fill from tape (i’m an old linear editor) and straight sounds like how things work in after effects.

i’ll try those options and see what i get.

cheers