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Rendering in cs4 with alpha channel

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Brendon Sulesky
Rendering in cs4 with alpha channel
on Apr 17, 2013 at 9:47:31 pm

I have looked at several tutorials for rendering alpha channel in after effects but all were for cs5 or cs6, and the tutorials didn't work in cs4 because either it didn't have the correct extensions or because when rendered all I got was a file or files with the file type "File" which doesn't work with any programs. I was able to open one of them and I did see that it may have rendered the alpha channel, but detail had been lost. You know, like there's alpha parts of the video and none-alpha parts and then parts in between that's sorta supposed to blend into the background to look more realistic. The parts in-between are now completely non-alpha, making it look really bad, if you know what I'm trying to say. Is there a way to render a file with alpha channel and keep the in between parts, and not have a file extension that's called "File" and doesn't work with almost any programs?


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Walter Soyka
Re: Rendering in cs4 with alpha channel
on Apr 18, 2013 at 1:40:56 pm

[Brendon Sulesky] "I have looked at several tutorials for rendering alpha channel in after effects but all were for cs5 or cs6, and the tutorials didn't work in cs4 because either it didn't have the correct extensions or because when rendered all I got was a file or files with the file type "File" which doesn't work with any programs."

The render queue hasn't changed a whole lot, so CS5/6 tutorials should be valid for CS4, too.

Can you walk us step-by-step through what you did?



[Brendon Sulesky] "I was able to open one of them and I did see that it may have rendered the alpha channel, but detail had been lost. You know, like there's alpha parts of the video and none-alpha parts and then parts in between that's sorta supposed to blend into the background to look more realistic. The parts in-between are now completely non-alpha, making it look really bad, if you know what I'm trying to say. Is there a way to render a file with alpha channel and keep the in between parts, "

It's probably fine -- it just sounds like you rendered straight alpha.

Please see Aharon Rabinowitz's Understanding Straight vs Premultipled Alpha [link].

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Brendon Sulesky
Re: Rendering in cs4 with alpha channel
on Apr 19, 2013 at 1:20:06 am

Yeah well every tutorial I've watched for cs5 or cs6 said to use quicktime and then put the selection in output module to alpha + RGB, but cs4 only has quicktime movie not quicktime, and quicktime movie apparently doesn't have alpha + RGB. I did what they said in the tuts though and put on the output module preset lossless with alpha and it starts with the format "video for windows". The channels under video output is set to RGB + Alpha and I change the color setting from premultiplied (matted) to straight (unmatted). I then choose "output to" and save it to the folder with the name I choose. Then I select render and wait for it to finish. Once it's done I see it is the file extension "file" and is incompatible with all but one program on my computer (VLC media player which I downloaded specifically for these). When I do open them in VLC media player I can clearly see that the alpha channel is screwed up, if it even rendered an alpha channel (I can't exactly find out because I can't use the file in any video editing software). All the parts of the video where the opacity is low is now full opacity which is not what I want. This is what I did, do you know what I did wrong or anything?
P.S. I just went ahead and brought the video I wanted to put this stuff over into after effects and just rendered it that way and that video is done, but I would still like to know for future projects.

P.S.S. I tried rendering the video with RGB + alpha again later with FLV, TIFF sequence and PNG sequence formats and they had pretty much the same results. Maybe there's something wrong with after effects?


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Walter Soyka
Re: Rendering in cs4 with alpha channel
on Apr 19, 2013 at 2:40:07 am

When you name the output file, are you inadvertently stripping the AVI file extension? Try leaving the .avi after the filename on the output module. You can add it back on in Windows Explorer by renaming the files you've already rendered.

Not all QuickTime codecs support alpha channels. Unless you select one that does, like Animation or PNG, you will not be able to select RGB + Alpha.

Please watch the video I linked to in my last post about premultiplied versus straight alpha. What you are seeing is perfectly consistent with straight alpha, and will look correct when imported into an application that understands straight alpha. I doubt that VLC will not show you alpha transparency.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Brendon Sulesky
Re: Rendering in cs4 with alpha channel
on Apr 19, 2013 at 2:35:11 pm

I don't know how I would be inadvertently stripping the avi file extension, so I cannot properly answer that question. As for being able to place the extension after the name and have it be that extension I did not know about that. I just watched the video in your link and I guess my only problem was I was rendering straight and not premultiplied. The only problem is he didn't explain how to composite straight in other programs so it doesn't look like crap. So I'll stick with premultiplied for now.


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Walter Soyka
Re: Rendering in cs4 with alpha channel
on Apr 19, 2013 at 3:37:35 pm

[Brendon Sulesky] "I don't know how I would be inadvertently stripping the avi file extension, so I cannot properly answer that question. As for being able to place the extension after the name and have it be that extension I did not know about that."

I just dusted off CS4 and tried this, and you're right -- even if you type over the file extension in the "Output to" save dialog, it adds it back in.

If you are using the "Lossless with Alpha" output module in a PC, then your output should be an AVI file. You can confirm this by locating the file in Explorer, selecting it, and press Alt-Enter to get its properties.

If AVI files appear as generic documents on your computer, there is some problem with your system outside of After Effects.

If you choose "Lossless with Alpha," leave the output module untouched, and Ae fails to render an AVI file, then Ae has some kind of problem.


[Brendon Sulesky] "I just watched the video in your link and I guess my only problem was I was rendering straight and not premultiplied. The only problem is he didn't explain how to composite straight in other programs so it doesn't look like crap. So I'll stick with premultiplied for now."

It depends on the other application. Some applications will attempt to guess whether to use a straight or premultiplied interpretation; others may need to be told.

What's the next thing you're trying to do with this rendered file?

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Brendon Sulesky
Re: Rendering in cs4 with alpha channel
on Apr 20, 2013 at 2:30:45 pm

I just want to use it in blender in the video editing section and add it to a video that I was making. I finished it now, I rendered the video I was doing in blender, then put the video in after effects and placed the layer of the animation over it. I found out later by rendering another animation in after effects, premultiplied, that bender is actually pretty good with alpha. It didn't have the black around the edges that were discussed in the video. Here is my finished animation that I wanted to add it to.

https://www.youtube.com/watch?v=-NYa0pII4PU

The subscribe animation at the end was the part I was having trouble with.


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