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Render Settings for Particular+Alpha Comp

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Irene Vega
Render Settings for Particular+Alpha Comp
on Mar 7, 2011 at 7:17:14 pm

Hi everyone,

I edited a video clip adding Particular effects. It's the first time I've ever used it and I would like to know what would be the correct/best settings to render the particulars with a transparent background (alpha)?

The thing is, since I'm working with other members of a team, we will assemble everyone's different effects in the videoclip. I used the footage as reference so I could place the particulars in certain segments. I used masks, pre-comps, lights, and motion tracking to place them, but I don't need the actual videoclip to show up, just the effects by their own.

So here are my questions:

-Before rendering, do I have to set my layers in the composition in a particular order? hide/show anything?

-In the render settings panel there is an Alpha and RGB+Alpha option, which one do I have to use? And if someone would explain to me what is the difference I would appreciate it (:

-No OpenGL? why?

-Also, for the compression, should I use the Animation codec/setting? I usually set this to H.264, but I've read it doesn't support alpha channels, is that right? Is there an alternative to the Animation setting so the file isn't too big? Does it affect render time?

Sorry for all the questions thrown out in here haha, I would like to have everything as clear as possible, since the render I'm doing right now is taking 2.45 hours /: and this information will certainly be of good help for future projects (:

Thanks in advance!! :D


P.S. I use AE CS4.


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Joey Foreman
Re: Render Settings for Particular+Alpha Comp
on Mar 7, 2011 at 9:01:14 pm

[Irene Vega] "-Before rendering, do I have to set my layers in the composition in a particular order? hide/show anything?"

Don't sandwich any 2d layers between 3d ones. Turn off the visibility for the background video that was your reference. If you hit the checkerboard icon at the bottom of the comp panel, you should see checkerboarding under your graphics. This isn't necessary for rendering, but just a visual reference to confirm that there is transparency to render. You can also see your alpha channel by clicking the RGB icon on the comp panel and choosing alpha. Again, this doesn't affect your render, it just let's you see the alpha you'll be rendering.


[Irene Vega] "-In the render settings panel there is an Alpha and RGB+Alpha option, which one do I have to use?"

RGB + Alpha. RGB is the graphics you created (the color info), Alpha is a grayscale image that defines the transparency, black being fully opaque, white fully transparent. Some applications require the Alpha channel to be separate from the RGB channels. Most non-linear editors and most compositing apps can read one that's embedded. You'll most likely want your alpha to be Straight, rather than Premultiplied.

For more info:

http://help.adobe.com/en_US/aftereffects/cs/using/WS08A8A927-0E3A-48a6-AFF9...


[Irene Vega] "-No OpenGL? why?"

It hasn't been fully implemented for all graphics cards and platforms, and can introduce errors into your renders.


[Irene Vega] "-Also, for the compression, should I use the Animation codec/setting?"

It depends. Do you know what app will be used for editing? I won't speak for Premiere or Avid, but if it's Final Cut Pro 7 I'd recommend ProRes 4444. It has greater bit depth, but a lower data rate than Animation. It's optimized for working with in FCP.

[Irene Vega] "I usually set this to H.264, but I've read it doesn't support alpha channels, is that right?"

Yes, that's right. And some NLE's can't edit it, FCP being one.


[Irene Vega] "Is there an alternative to the Animation setting so the file isn't too big?"

File size should be at the bottom of your priority list. High resolution, high bit depth, pristine graphics with transparency have large file sizes. You have to live with that. Fortunately, storage is cheaper than it's ever been, and getting more so all the time.

"Does it affect render time?"

High resolution, high bit depth, pristine graphics with transparency take a while to render. You have to live with that, or buy a faster computer. They don't currently make ones that are fast enough;), though render farms can help.

Joey Foreman
Editor/Compositor/VFX Artist


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Irene Vega
Re: Render Settings for Particular+Alpha Comp
on Mar 7, 2011 at 9:29:02 pm

Thanks for your responses!

Yes, I definitely need to do some research regarding alpha and compression, it's just I haven't had the time yet and needed some quick advice being that this project is due tomorrow Dx

[Joey Foreman] "If you hit the checkerboard icon at the bottom of the comp panel, you should see checkerboarding under your graphics."

Okey, I did, hid the video and clicked "toggle transparency grid" and all i can see is the particulars over a black background /:

[Joey Foreman] "You can also see your alpha channel by clicking the RGB icon on the comp panel and choosing alpha."
When I clicked this, everything turned white.

I don't think there is transparency to render, right?.. but I'm not sure, how can I change this?


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Joey Foreman
Re: Render Settings for Particular+Alpha Comp
on Mar 7, 2011 at 11:22:31 pm

I don't know. You must have an image layer or a background solid that's filling your comp under the particles.

Can you post a screen grab of your AE interface, showing all of your layers?

Joey Foreman
Editor/Compositor/VFX Artist


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Joey Foreman
Re: Render Settings for Particular+Alpha Comp
on Mar 7, 2011 at 9:42:20 pm

[Joey Foreman] " Alpha is a grayscale image that defines the transparency, black being fully opaque, white fully transparent."

Sorry, that should have said the reverse. Black is fully transparent, white fully opaque.

Long day.

Joey Foreman
Editor/Compositor/VFX Artist


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Irene Vega
Re: Render Settings for Particular+Alpha Comp
on Mar 7, 2011 at 11:37:45 pm

Oh God. You've no idea how relieved I felt xD haha! So if my final render shows the Particulars over black background, it rendered correctly??


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Joey Foreman
Re: Render Settings for Particular+Alpha Comp
on Mar 8, 2011 at 12:30:26 am

No, sorry. Our threads got crossed and you've misunderstood. The black and white pixels I referred to are what make up the alpha channel itself. I still don't know why you weren't able to see the alpha in alpha view in the composition. You should have been able to.

The black in your render is no sure sign of your clip having an alpha channel. It could just be black pixels rendered in the RGB channels.

Import your render back into AE. In the project panel info, you should see millions of colors +.

Drag this to the make new comp icon, click the channel display icon in the comp panel, and choose alpha. Your particles should appear as white on a black background. If you just get a fully white image, then you don't have transparency.

If not you have to go back to your comp and figure out what's filling up the comp and preventing the transparency being rendered.

Joey Foreman
Editor/Compositor/VFX Artist


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Irene Vega
Re: Render Settings for Particular+Alpha Comp
on Mar 8, 2011 at 5:51:06 am

Baw.. yeah the thread kinda messed up and I thought I had got it right.

Anyway, I tried what you told me and, indeed, the black background has no transparency. I checked my 238423856965 layers and what i found is that there are some black Solids I used as background to add some glow with adjustment layers (using fast blur) to the Particulars. What I noticed is that, when I delete this solids, I finally get the transparency I need, but the new problem is that the Particulars don't show up anymore over the video.

This is a screen cap:



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Joey Foreman
Re: Render Settings for Particular+Alpha Comp
on Mar 8, 2011 at 2:54:13 pm

I can't relate your description of the problem to what I see in the screen cap. I see a Particular layer above a black solid, but it appears you've deleted the video layer you were compositing over.

Bring your video layer back in and turn off the solid. If you can't see the particles over the video, then you'll need to adjust the Particular effect parameters until you can.

Don't forget that you can always set your video layer to be a Guide Layer. That way you don't have to turn it off or delete it before you render.

Joey Foreman
Editor/Compositor/VFX Artist


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Irene Vega
Re: Render Settings for Particular+Alpha Comp
on Mar 12, 2011 at 6:06:24 am

Sorry for the late response. I should have explained the screen cap a little bit better.

The image shows one of the many pre-comps I created for the main composition. The selected layer is the solid I've been having trouble with. Every pre-comp I created (about 20 more or less) needs it for the glow (created with fast blurs) to show up. When I turn them off (in every pre-comp I have), I finally get the transparency I need, but in my main comp the particulars stop showing.

I hope I can explain myself better with these screen caps.

Here's an image of the main comp:


Every pre-comp looks like this:


Each solid in the pre-comp creates the black background that blocks the alpha/transparency I need. But when I hide them, the Particulars disappear:


And when I go back to my main comp, they are also no longer visible:


When the solids are not hidden, the Particulars show but there is no transparency.


I hope it's clearer this time.
So does anyone know a possible solution that might prevent the Particulars to disappear when I hide the solids so AE can render an alpha channel?


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Joey Foreman
Re: Render Settings for Particular+Alpha Comp
on Mar 12, 2011 at 8:54:41 pm

Okay, so it looks like you're creating your particles as inverted luma mattes, and I don't really understand why.
Why not turn off the solid at the bottom, set the Track Matte on the particular layer to None, and turn off the blue solid above it?

I'm just not following the logic behind the track matte scheme you've set up.

Joey Foreman
Editor/Compositor/VFX Artist


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Cassius Marques
Re: Render Settings for Particular+Alpha Comp
on Mar 10, 2011 at 9:44:13 pm

You're probably getting black instead of alpha because of some effect you applied on those adjustment layers, you have to make sure to use only effects that can render over transparent, You see the video when it is below everything because you have set them(the effects) to screen.

The worst problem is that you can't rely on multiple blending modes, the person responsible for compositing it after wont be able to differ the layers and will only be able to set one blending mode. It is going to look different.

Bottom line is from that screenshot you are using the particles set to normal and some random effect to screen... You wont be able to have both...so on that case I suggest rendering 2 files. Particular with alpha and whatever else you're using screen, over black.


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Tudor "Ted" Jelescu
Re: Render Settings for Particular+Alpha Comp
on Mar 7, 2011 at 9:04:04 pm

It looks like you may benefit of some reading regarding alpha channels and compression.
For best result in VFX you want to work at the highest possible resolution and color depth, without any quality loss all the way to the final render. Once you do that then you go on to compressing the final piece for playback. So yes, you will have big size files.
Render settings: "Alpha" renders out the alpha channel only. "RGB+Alpha" will give you the color information and the alpha channel in one file. You want to render to an uncompressed codec or file sequence. Best is to use file sequences- TGA or uncompressed TIFF.
When you work with particles though, it is best to render out the final comp and not the particles with an alpha and then composite, especially if you are using a different blend mode than normal.

Tudor "Ted" Jelescu
Senior VFX Artist


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