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Export rotobrush matte to softimage (i.e. invert it)

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John Estes
Export rotobrush matte to softimage (i.e. invert it)
on Jan 19, 2012 at 5:54:24 pm

Okay so I did the rotobrush and got the matte I wanted.
Alpha channel view shows a white as transparent.

When I export video with alpha premultiplied it will not work inside softimage.

When I go to composition export a still frame it works fine as I can invert the matte in softimage.

As far as I can tell, the still photoshop layer preserves the matte and somehow the video looses it. I have tried all types of export.

Any suggestions on why a still psd frame export works and a video with alpha doesn't?

A sincere thanks for anyone who is willing to help.

John



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Erik Waluska
Re: Export rotobrush matte to softimage (i.e. invert it)
on Jan 19, 2012 at 8:45:47 pm

I'm a Softimage user too, but not a guru. First, in what format are you rendering out the movie file? I have found that Softimage prefers image sequences or AVIs but not Quicktime movies. Try rendering out a PNG sequence with a straight alpha from AE. You can extract the alpha with a channel picker node in Softimage.


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John Estes
Re: Export rotobrush matte to softimage (i.e. invert it)
on Jan 20, 2012 at 1:45:59 am

Erik,
Nice to have a softimage user! I feel like I am in the minority there. I rendered out a .png sequence, and confirmed the alpha in nuke and in sony vegas. But when I put it in softimage and use the alpha as a transparency map, it doesen't work. Not sure what you are referring to as the channel picker node, but I will see if I can find it.

As an aside, do you know how to get the still image sequence to play back in the preview window like a .avi does. All it gives me is the first still image ( just a seperate question for you).

Thanks,

John



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Dave LaRonde
Re: Export rotobrush matte to softimage (i.e. invert it)
on Jan 19, 2012 at 9:22:03 pm

There's a litany of things to do to get a movie with an alpha channel. First is to select a codec that supports alpha channels. Have you imported the rendered clip into AE to confirm transparency?

If you know the whole alpha channel drill, could it be the difference between Straight and Premultiplied alpha channels?

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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John Estes
Re: Export rotobrush matte to softimage (i.e. invert it)
on Jan 20, 2012 at 1:40:35 am

Dave and Erik thanks for your responses.

Let me try to get more in detail for you. I am generally knowledgable but not an expert in either application.

So, I rotobrushed a sequence in after effects. Specifically removed the foreground element.

Confirmed that there is a alpha Matte generated via the channels button. Image is black background white subject isolated.

My intent would be to export to an .avi that can accept alpha channels as the 4th channel. Inside Softimage I should be able to invert the channel but that doesn't work.

From after effects:

I use cineform ( now GOPRO) as an intermediate codec.

In after effects, I selected it as the codec and confirmed RGB + alpha for render.

I rendered as lossless ( required by cineform to do the alpha channel thing).

( I have confirmed the presence of a RGBA it inside Nuke with alphas in tact as it deals more clearly with this stuff as far as I can tell ).

I bring it into softimage. Apply a phong with a image texture ( the .avi I expored with the alpha channel) and then inside the shader property page, I apply a transparency map by going to the ppg transparency tab and select the "use alpha" to use for the transparency (here I have the chance to invert it) When I do I get some funky half transparency.

Doing the same process with a still image exported from the composition ( that appears to be inverted) gives me a transparency (white) + RGB channel with a alpha transparency as it should be. But thisthing gets long and drawn out. Bottom line the same doesn't work with the .avi.



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Dave LaRonde
Re: Export rotobrush matte to softimage (i.e. invert it)
on Jan 20, 2012 at 2:13:00 am

Well, you did everything except the one thing I asked: did you import the rendered file into AE to confirm an alpha channel?

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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John Estes
Re: Export rotobrush matte to softimage (i.e. invert it)
on Jan 20, 2012 at 3:55:41 am

Dave,
Sorry. Is there a specific way you would like me to do that? I can import an image in and then in the footage pane (where you can switch from RGB to alpha) and it shows the alpha channel.

Here is the thing, I import to Nuke composting software and it shows no alpha on the video, but does on a image sequence. Then I import it into Vegas software and select it to be interpreted as "dirty" and it shows the transparency. So it seems to vary by software as to its being recognized. But I think the answer to your question is yes. Seems to show an alpha channel.

Though I can get confused on this, as far as I can tell it has an alpha channel. I just downloaded the new cine form as further research made the alpha support questionable.

Is there another codec for video that supports an alpha channel I can try? I prefer to avoid an image sequence.

Thanks

John



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Dave LaRonde
Re: Export rotobrush matte to softimage (i.e. invert it)
on Jan 20, 2012 at 3:46:30 pm

When you import alpha channel footage into AE, it guesses at the the proper alpha channel interpretation by default. There are two: Straight and Premultiplied.

Then make a comp quick-like. Add a colored solid to it. Add the footage you've ALREADY RENDERED IN AE to this comp as the uppermost layer. If it shows up the way you expect it to, look at the Interpret Footage settings. They should tell you if it's Straight or Premultiplied.

I suspect you rendered one kind of alpha channel, but the application in which you want to use it needs the other kind, or you need to change settings in the other application.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Erik Waluska
Re: Export rotobrush matte to softimage (i.e. invert it)
on Jan 20, 2012 at 4:12:23 pm

I agree with Dave that the alpha type is the most likely suspect. If not, could you post a screenshot of the shader setup you are using with the transparency settings?


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