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how to map an alpha+ avi onto a plane

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adeeb oberoihow to map an alpha+ avi onto a plane
by on Jan 15, 2011 at 6:24:12 am

I would like to map an AVI of a chroma keyed dancer onto a plane in 3ds max and make the plane transparent so that you only see the dancer in the render.
I have 3ds Max 2010. What is the best way to do this???

Can any one advice me on this, I am stuck with a project I am working on.


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Graham MacfarlaneRe: how to map an alpha+ avi onto a plane
by on Feb 5, 2011 at 3:11:42 pm

* Are you using Scanline / Vray / MentalRay / etc... ?
* Does the Avi contain an alpha channel or do you have a separate avi or image sequence with the black and white alpha information?

(I would recommend not using avi files as an asset in Max, try using an image sequence instead, as Max then only needs to load one image at a time rather than loading a whole avi to playback one frame.)

Also, if you have any damaged or conflicting codecs on your system you risk stability problems in Max.

Graham Macfarlane
3D animator and VFX specialist
London UK


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adeeb oberoiRe: how to map an alpha+ avi onto a plane
by on Feb 11, 2011 at 5:28:23 pm

Hi, thanks for the reply.

I am using the normal standard Max render.

I did have an avi with alpha channel but it didnt work.

Now I also rendered the same footage with a white mask reset the materials. I feel its a big work around but it does work. Strange that Max does not see an alpha channel, other 3d applications do.

What kind of sequence do you suggest for usage in Max?

Another problem I am running into is after I render the Max file in RPF and want to use the 3d channel in AE, the depth of field sees the whole plane and not only the keyed footage.

Regards,

Adeeb


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Graham MacfarlaneRe: how to map an alpha+ avi onto a plane
by on Feb 11, 2011 at 8:41:09 pm

I'm sure the avi with which contains the alpha channel will work in max as long as you have done the following:

* Load it into the diffuse slot of the material
* Load again (or make a copy but not instance of the diffuse slot) into the opacity slot
* Within the opacity slot make sure that the Mono channel Output is set to alpha.

For any animation that Max needs to load into a scene I go for either JPG, PNG or TGA normally.

If lossless compression is not too important and file size is of concern then go for a JPG with max quality. It provides one of the lowest files sizes around can be created/saved very fast and caches into RAM fast too.

If lossless compression is important but file size still an issue then I'd go for PNG (non interlaced). Gives a moderate file size, is created/saved fairly quick although caching can be a little slow.

If lossless compression is important and file size is of no concern go for TGA with RLE compression. Large-ish file size, is created/saved lightning fast and cashes like a bat out of hell too!

I always find it important to consider how fast image sequences are to make and work with when considering which to go for on a project. If the sequence duration is quite short then it wont matter much but if your dealing with a very long sequence, any app (Max or AE) will take longer to render or load the frames and slow you or your rendering down.

As for your last Q, don't use Scanline!! Scanline zdepth cannot understand opacity in surfaces and views them as opaque. Vray for example (and probably most other 3rd party renderers) would solve this issue for you out of the box.

Graham Macfarlane
3D animator and VFX specialist
London UK


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adeeb oberoiRe: how to map an alpha+ avi onto a plane
by on Oct 6, 2011 at 2:27:05 am

Hi Graham,

I have an other similar project coming up, I plan to use your advice above.

You suggest not to use scanline but Vray, thing is, the project was just build in scanline. Is there any other option to get z depth information on transparent planes?

Looking forward to hearing from you,

Adeeb Oberoi


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Graham MacfarlaneRe: how to map an alpha+ avi onto a plane
by on Oct 6, 2011 at 12:47:43 pm

If you have access to a compositing package then one work around could involve the following workflow:
1) Render off your animation (with scanline) without the transparent plane at all (a background render pass).
2) Render the plane with no transparency (Plane pass).
3) Render off the plane again but only showing the black and white keying information (Plane transparency pass).

Lastly, comp all three render passes together in say After effects.

Example AE composite structure:

* Plane pass (using opacity from: Plane transparency pass)
* Background render pass

Hope that helps

Graham Macfarlane
3D animator and VFX specialist
London UK


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adeeb oberoiRe: how to map an alpha+ avi onto a plane
by on Oct 19, 2011 at 9:51:44 pm

Thanks, It helps.

Problem I have now is that your previous advice doesnt work
Your advice was:

* Load it into the diffuse slot of the material
* Load again (or make a copy but not instance of the diffuse slot) into the opacity slot
* Within the opacity slot make sure that the Mono channel Output is set to alpha.

The last step doesnt work, I can not set the mono channel output to alpha somehow. When I move over it the little hand shows and I can not select.

Hope you can help.

Regards,

Adeep Oberoi


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Graham MacfarlaneRe: how to map an alpha+ avi onto a plane
by on Nov 2, 2011 at 2:53:46 pm

If you can't set the mono channel output this means that the asset you have loaded into Max contains no alpha channel.

That previous workflow I suggested is not really applicable any more, since you should no longer require the use of the opacity slot.

The latter workflow I suggested requires you to render off that 3rd pass with the plains alpha information displaying from the diffuse slot of the material so that the plain's alpha is directly renderable as a solid surface(eg alpha = 1)
This allows you to cut the plain out in post rather than at render time, which will solve your zdepth issues.

Graham Macfarlane
3D animator and VFX specialist
London UK


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