Alpha question

[agep]

I do have a chor setup containing a dome and a character. I use the dome with an hdr image for reflection (reflection map on a material on the character itself is out of the question). So my problem is this: I need to render an animation with only the character (alpha) eg make the dome cast shadows but not make it visible in the render... Any tips?

[KenH]

Would this do it? If you use targa in the render options, you get an alpha option. If this is on, the models will be "separatable" from the background color. If you select OpenEXR then there are more options.

[agep]

If this is on, the models will be "separatable" from the background color

The point is that Im not using the backgroundcolor, but an actual model as background (the dome), which gives me an all white alpha. What Im looking for is an model option such as "include in alpha" or something like that

[thefreshestever]

i´m not really sure, but yves wrote on his site about skydomes that you could set a skydome to 100% tranparency and it will still cast reflections (if "cast reflections" is turned on for this model of course...)...

but i don´t know how a:m will handle the alpha channel then.... is a model that´s completely transparent completely excluded from the alpha? should be i´d say....

[Fuchur]

i´m not really sure, but yves wrote on his site about skydomes that you could set a skydome to 100% tranparency and it will still cast reflections (if "cast reflections" is turned on for this model of course...)...

but i don´t know how a:m will handle the alpha channel then.... is a model that´s completely transparent completely excluded from the alpha? should be i´d say....

 

The easiest way to handle this: First render everything out like you want it (color-wise), than deactivate every light and render again. Now use the second image as an alpha-channel in your 2d-programm and everything should work.

 

*Fuchur*

[agep]

is a model that´s completely transparent completely excluded from the alpha? should be i´d say....

It sure is excluded from the alpha, but doesn't cast reflection though

[agep]

easiest way to handle this: First render everything out like you want it (color-wise), than deactivate every light and render again. Now use the second image as an alpha-channel in your 2d-programm and everything should work.

That is my backup plan... But since it is an animation it sure would be nice to have it all in one;)

[agep]

Since the camera is static during the animation, my second backup plan is to actually just cut out those patches in the dome that are visible in the camerafield, I don't think that is going to be noticeable in the reflections. Need to do a few tests

[HomeSlice]

easiest way to handle this: First render everything out like you want it (color-wise), than deactivate every light and render again. Now use the second image as an alpha-channel in your 2d-programm and everything should work.

That is my backup plan... But since it is an animation it sure would be nice to have it all in one;)

 

Since the second "alpha channel" render will only be used for the alpha channel, you can just render it in "Shaded" mode with "16 polys per patch" resolution (after you turn off the sky dome of course). That should go much quicker than the first pass.