Gbanvl
08-23-2005, 07:48 PM
I made a simple model a couple of days ago and quickly did a setup for natural light using the Max scanline renderer and skylight.
http://www.flickr.com/photos/sightrays/35984790/in/photostream/
Then I started experimenting with Mental Ray materials and wanted to try to use them in a virtually identical scene with the same kind of lighting effects.
http://www.flickr.com/photos/sightrays/36571355/
For the second image I made a basic, light gray material, and substituted a MR area Spot for the Max Direct light with area shadows that I had been using for the key light.
<p>I know that in order to get any effect from skylight in Mental Ray you need to turn on Global Illumination and Final Gather, so I've done that. But I haven't changed any of the other Mental Ray settings.<br>
The problem as I see it is that I am not seeing any shadows cast by one object upon another by the skylight, and I should. Skylight does seem to darken the armpits of the model a bit, but does nothing to darken the shadow the model casts on the floor, and the floor object does not occlude the skylight on the botton surfaces of the model as it does when using the scanline renderer.
<p>I would use ambient occlusion to substitute for skylight but that would mess up the backdrop I have set up, a shadow/matte material that merely recieves shadows so that it can blend with whatever background I choose to use.
<P>Adding a map to the skylight doesn't seem to help either. I have a gradient from white at the top to black at the bottom that I sometimes apply to the skylight when doing renders where I don't include a floor. That works in the scanline renderer in Max, but doesn't seem to work for me in Mental Ray.
<p>I'm sure there must be a simple solution to this but I don't know enough about global illumination techniques yet for it to occur to me.
http://www.flickr.com/photos/sightrays/35984790/in/photostream/
Then I started experimenting with Mental Ray materials and wanted to try to use them in a virtually identical scene with the same kind of lighting effects.
http://www.flickr.com/photos/sightrays/36571355/
For the second image I made a basic, light gray material, and substituted a MR area Spot for the Max Direct light with area shadows that I had been using for the key light.
<p>I know that in order to get any effect from skylight in Mental Ray you need to turn on Global Illumination and Final Gather, so I've done that. But I haven't changed any of the other Mental Ray settings.<br>
The problem as I see it is that I am not seeing any shadows cast by one object upon another by the skylight, and I should. Skylight does seem to darken the armpits of the model a bit, but does nothing to darken the shadow the model casts on the floor, and the floor object does not occlude the skylight on the botton surfaces of the model as it does when using the scanline renderer.
<p>I would use ambient occlusion to substitute for skylight but that would mess up the backdrop I have set up, a shadow/matte material that merely recieves shadows so that it can blend with whatever background I choose to use.
<P>Adding a map to the skylight doesn't seem to help either. I have a gradient from white at the top to black at the bottom that I sometimes apply to the skylight when doing renders where I don't include a floor. That works in the scanline renderer in Max, but doesn't seem to work for me in Mental Ray.
<p>I'm sure there must be a simple solution to this but I don't know enough about global illumination techniques yet for it to occur to me.