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Z space clipping plane

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bart stevensZ space clipping plane
by on Nov 9, 2010 at 8:23:49 pm

I'm having some difficulty trying to define a positive Z space clipping plane.
I have a very simple composition.
I have text animating on a circular mask with the center at 0,0,0.
I have no problem setting up my " Z-plane" and making the positive Z space (or further from my camera) masked out.
I used a square comp with a white solid for my "clipping plane" and placed it in 3D space at 0,0,0.
The "clipping plane" solid is above the text path in the composition window and set it to "silhouette alpha" mode.
The challenge is creating the opposite mask.
I want to make the positive (or closer to the camera) masked out.
The end result would be two compositions one for positive Z space, and one for negative (foreground and background compositions).
Ultimately this is part of bigger project, where the composite has an actor standing in the middle of a circle.
Any ideas?
Thanks,
B


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Dave LaRondeRe: Z space clipping plane
by on Nov 9, 2010 at 9:44:32 pm

It sounds to me like you might be overthinking this.

If you want text to circle a subject, you make a circle of text, key or mask out out the subject, and put the two on a background.

Am I missing something here?

I had to look up the term "clipping plane" because I had never seen the term used in After Effects. The first thing that came up was an Open GL page. If you're new to AE, here's a tip: don't use Open GL for rendering in AE. The guys at Adobe don't use it. Kapiche?

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


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bart stevensRe: Z space clipping plane
by on Nov 9, 2010 at 10:09:17 pm

thanks for the feed-back Dave,
Yes, might be over-thinking (wouldn't be the first time).

If all my objects were 3D layers, that solution would work fine.
I should have clarified the final composite.
I'm using a combination of live action footage (green screen key)
and the rendered "c.g environment" from my 3D animation package (XSI).
I've split my renders from my 3D animation package into foreground and background layers (defined by the "0" Z plane). The actor is in the middle of background and foreground objects ( in the center of the circle).
Although the renders are from a 3D environment, the renders are 2D layers in my composite.

I've exported my camera data from xsi, so I can combine After Effects 3D (text around circle mask) with my 3D animation (xsi) 3D.

Since my cameras are matched, I want to utilize AE for elements that could render a lot quicker.
So I'm trying to define my After Effects composition the same way and divide foreground and background at the "0" Z plane.

- Clipping planes are not a part of AE, but I didn't know how else to express what I'm trying to accomplish.

Kapiche - on the Open GL ( double checked it was off)

Thanks
-Bart


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Dave LaRondeRe: Z space clipping plane
by on Nov 9, 2010 at 10:28:26 pm

It sounds simple enough: put the camera and chroma-key footage in as 3D layers, then put the foreground ABOVE the camera layer in the comp timeline, the background below the 3d layers in the comp timeline. AAs long as you keep all the 3D layers together in AE, you should be good to go.

Alternately, just do the keying in AE, then use the resulting alpha-channeled footage in your 3D application.

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


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bart stevensRe: Z space clipping plane
by on Nov 9, 2010 at 11:23:23 pm

Thanks for the feedback,
yeah that solution would work, but I want my 3-D text in After Effects to wrap in front of my rendered (2d element) foreground and in back of my rendered (2D element) background.
I thought about bringing the keyed actor into my 3-D application, but I really want to keep them separate until the final composite for better control of all the elements.
I can render the "text wrap" in my 3-D application (xsi), but I just figured there must be a way to "cut in half"(by the Z axis) the After Effects composite.
Hopefully I'm communicating the challenges accurately.
Thanks for your assistance.
-Bart


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Walter SoykaRe: Z space clipping plane
by on Nov 9, 2010 at 10:51:51 pm

Just a quick idea -- if you absolutely need to use a clipping plane, maybe you can use depth passes from XSI for your compositing objects. Render them out along, import them into AE, tweak the threshold and levels, and use them as luma mattes for one side and inverse luma mattes for the other for each compositing object.

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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bart stevensRe: Z space clipping plane
by on Nov 10, 2010 at 12:03:10 am

Thanks for the idea, I've played around with generating depth maps from xsi, but I'm not sure that would accomplish what I'm trying to do.
The After Effects project really just needs to be split in two by the Z axis. I need it to be either A(foreground) or B (background).
The goal is to incorporate AE 3-D layers with rendered 2-D images from XSI. Not sure if I'm communicating accurately or not.
Thanks for the assistance, not many working with XSI and AE.


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Roland R. KahlenbergRe: Z space clipping plane
by on Nov 10, 2010 at 10:24:22 am

I'm with Dave on this one. You should be fine if you set your Maya renders in AE as 3D layers. Do likewise for the chroma footage.

Give that a shot and let us know of the results.

Cheers
RoRK

AE Training in South East Asia. AE templates for sale and rental. Click here for more


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bart stevensRe: Z space clipping plane
by on Nov 10, 2010 at 4:34:15 pm

Since I've exported my camera from my 3d animation software (xsi), if I set my renders as 3D layers they would act like 3D planes when being represented by my camera. I tried that idea with collapsed transformations, but that was unsuccessful too.

Finally got it figured out though...
Obvious answer there all along.
I just combined the comp with the positive Z space "masked out" as my bottom background element (2D pre-comp with same camera). And I use the same comp without the mask as my top foreground element.
Definitely over-thinking this one.

Thanks for the feedback everyone.


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