Need help with Radiosity compositing

[ariander]

http://ariander.com/wip/hdri_compositing/testrender2.jpg

This is the plane with the image in the lumonicity chanel, but as you see the radiosity-shadows on the floor disapear.

[AdamT]

This is a reply I clipped from the forum a few months ago: works quite nicely:

"A tutorial how to fake a floor is in progess. Because of my pour english, audity from renderosity will translate it soon.
Here a short description how I make it:
- use the sample-scene from dosch (add a hdri-map to the spheres)
- place a disc in the scene, where the floor should be
- place the objekt on the floor
- make all objekts, exlude the sphere witch is visible for the cam + refelction, invisible for the renderer
- render the image in the final resolution you want
- make all objects visible
- make a new material with the rendered image in the color-chanel
- map the new material with frontal-mapping on the disc
- set the saturation (radiosity) for this material in the material-manager to 0%
- make a new material, map it by plane on the disc and rotate it, so that it lies on the disc
- use the function "fit to object" in the object-manager
- let the texture-tag select
- edit the first material with the rendered image
- put a sla-projector in the alpha-chanel
- edit the projector
- set the projection to "plane"
- use "copy tag" to get the settings of the second material
- use a circle-gradient as the shader
- the color should range from white to black
- delete the second material from the disc

That´s it. You maybe have to make a composite-tag for the disc, so that it don´t cast shadows. I deactivate the "generate radiosity" for the disc and the other objects. That´s faster and look also good. The rest is testing ;-)

__________________
CU,
holle."

So the key is the circular gradient, which fades the projected background into the real background.

[ariander]

Thanks AdamT!
I'll try that..

[maced]

Try:

http://www.ek3d.at/tutorial/ektutorial-n1.html

http://www.maxoncomputer.com/tutorial_detail.asp?tutorialID=243&site=

[designresponse]

Use a shader called 'Shadow Catcher' on a floor plane or disc and your background can literally be a background image. The shader will just render as shadows only giving the impression that a floor is there.
I don't know where I got this shader from but it is very useful, somebody else might be able to help you with a link to it.

Peter

[Peoples]

Hi!

This render is made with my own HDRI image and the BG picture taken from the same place as the HDRI. I put the bg image in the color channel of a material and assigned that material to a floor w/ frontal mapping and a background object. I used a sky with a composite tag seen by camera unchecked. The hdri material is on the sky object. This is the result I got:

http://www.hut.fi/~vhautala/renders/audiComp.jpg

[hundredthirtyseven]

I don't know if this is relevant, but: what to do when HDRI shadows aren't enough? I mean with simple radiosity GI (no HDRI) you can still use the "shadow" menu of the light object, so you can still cast some extra shadows if radiosity can't, but with HDRI it is not possible, because you don't have shadow options under the luminance channel or under the compositing tag. Or is it possible? Cause sometimes (most of the time) HDRI shadows are really dull.

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