Adding separate objects to a scene?

[cgboy]

Hi, hope i can help. But Firstly need to clarify what is it you really want.

1) Do mean how do u composite render passes into a existing background?

There are 2 ways of compositing: layer based and node based? either way you just need plenty of alpha channels setup already when u render these files.

or

2) Do you mean you want to setup it all in a 3d program so you render all the different passes/layers (depend how u set it up)?

I think if your question is about Creating Alpha channels. Right?

If you created anything in 3d you will get automatic an alpha channel, just depend what file format u save. targa has good alpha but file size is large. i usually just use simple .png with transparent forr simple composites. really depends on your target platform medium to be used.

Well there are many ways in doing things in 3d but usually in a 3d program it seems u need a matte material (example from 3dsmax) to applied to objects you do not want to include in your renders but want to include shadows, reflections etc.. and render this out to composite to your original render passes. Cause this matte gives you alpha channels in your renders to remove anything you do not need when compositing

Many people use a few copies of their original scenes and just turn on/off what they need with this technique to combine in a compositing program.

Anyways i usually will render the background last with its own pass so i have a clean layer for other renders to be composite on top.

hope that helps.

[cwisbg]

i kindof figured it was the alphas, but in photoshop the alpha channel is just white. and how do i get everything except the object to be transparent?

[cgboy]

Hmm in this case well usually i would try to setup my scene with the object i want to isolate and put a matte material to what i do not want to render with the objects.

then render it with alpha channels. u then should see some black in the alpha channels.

if its all white, one Case is you might have lots of cg elements that cover the whole scene. that is why the matte/shadow material is important to mask out the other objects.

If you do not want to rerender or setup it all agian. usually we will then go the hard way by hand painting and rotoscope the alphas to isolate the objects.


try render just putiing a sphere. u will get a white circle alpha rght. cause there is no background. if thereis then u will too get all white if the background was created in 3d.

Again try playing with the matte material applying to the background elements and rerender u should see the differences.

hope that helps again.

[cwisbg]

That makes sense, my scene is packed so that is most likely why it dosnt have alphas. Thanks

[cgboy]

no worries, hope that helps, let me know when u finish. curious to see how it turns out.

:)

Jimmy

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