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Bad Alpha Bad! ( posted on apples site as well)

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michael del rossi
Bad Alpha Bad! ( posted on apples site as well)
on Oct 18, 2005 at 11:02:42 pm

Ok boys and girls,
have any of you came across this problem.
The alpha channel is smaller than the effect.!!!!
When I put a glow or light rays on a text object the alpha channel is not as large as the effect
go look at

I'm using motion2 the layer is set to either combine or normal (doesn't matter)
why did apple decide to arbitrarily make the alpha smaller??????
There they go thinking different again!!!!!!
and I love Apple and macs but this is really the last straw for Motion first the stupid way the handle fade in and out with the drop shadow coming through the white text( yeah I know i have to animate the levels filter on the alpha channel)
this is for a film out and the lab needs to have the alpha for overlay Arrrrgh!!!
thanks for your help this is the program I hate to love

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Martin Baker
Re: Bad Alpha Bad! ( posted on apples site as well)
on Oct 19, 2005 at 7:27:02 am

If you hover the mouse cursor over the middle of the I and N, the alpha channel values read out at around 90 and this tallies with the image when viewing just Alpha. The problem seems to be the Brightness filter, because it's flaring out the RGB channels but not affecting the alpha at all. So use the Levels filter instead, twirl down to reveal the sliders and set Alpha>White In to 0.2. Seems to do the trick here.

Digital Heaven, London UK
NEW! VideoSpace - free diskspace calculator widget

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michael del rossi
I think I got it figured out
on Oct 19, 2005 at 4:17:27 pm

Here's what I'm doing:

1) create motion file
2) add text and effect (directional blur and brightness)
3) export tiff seq tif+alpha
4) premultiply on
5) bring into AE to check before sending to lab for output (the lab I'm using uses AE for compositing scanned film and my graphics layer to print)
6) Alpha is smaller than color

7) go back to motion and hit the "v" key to toggle between color and alpha lo and behold the alpha IS smaller than color.

Project properties
8bit background color black 0% opacity

Here is the kicker
1) bring in a background into Motion and the effect looks correct

2) bring into Combustion and click on "Premultiplied with" in footage controls effect looks correct

3) Bring into AE (alpha shows up as straight)

load into composition alpha looks smaller

till you set the "mode" pull down to "Luminescent Premul" Voila!!!!
effect looks correct!!

The communication between Motion and AE seems to be the problem.
There is no difference when I click on premultiply in AE interpret file dialog box ! (and yes I reloaded the footage).
Also When I bring the file into Photoshop the alpha appears small as well.

The question I still have is why when I have sent out files for the last 10+ years with alphas there has never been a problem.
I've gotten files with alphas and as well and no problems.
I'm not that lucky ;/)??!!

anybody have any ideas why it works this way?


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Jim Kanter
Re: I think I got it figured out
on Oct 20, 2005 at 7:47:51 pm

Have you tried importing the motion project directly into AE instead of an image sequence?

Jim Kanter,
Digital Film Institute

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michael del rossi
Re: I think I got it figured out
on Oct 21, 2005 at 12:26:29 am

I am just checking the files as they will be output to film and the lab uses AE to composite files.

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