How to Render RGB Light Pass in 3Ds Max

[soulburn3d]

What do you mean by RGB Light pass?

- Neil

[Aneks]

apply a white shader to your model. either a constant or something without specularity. Use completely saturated red, green or blue for you lights. ie RGB : 255 0 0

[rendermaniac]

Just make your lights saturated red, green and blue and your surfaces white.

The problem with this approach is that reconstructing the colours in 2d can get tricky - you will get a lot of problems with aliasing on edges and anything with opacity will not work. If you try this for hair it will look awful as you get both these problems in abundance.

The edge problem comes because you will need to multiply images together. This will multiply the filtering by itself, making it much harsher. You can get around this by antialiasing in 2D, but that means rendering out really huge images and resizing them later - not really a good saving.

The opacity problem is because you need to multiply surface colours by opacity, and THEN over them on top of each other. The order is important. 2d images are already composited and you can't go back to the (3d) opacity.

A better approach is to rennder out each light seperately - you then just add them together. RenderMan and Mental Ray both support outputting all these passes from a single render.
There is information on how to do this with RenderMan here (rendering lights seperately and simultaneously) http://renderman.org/RMR/Examples/srt2002/index.html#aov

The only case where I'dconsider multiplying CG elements is maybe a shadow or ambient occlusion pass.

Simon

[leoraphael3d]

Thank you very much Rendermanic. It was very helpful tips.
Regarding renderman I have no idea of the renderer. Can you let me know if there are any tutorials for Mental ray with max

Thank you

Best regards
Raphael

[rendermaniac]

With Mental Ray there is a shader called ctrl_buffers by Francesca Luce
http://forums.cgsociety.org/showthread.php?t=209991&page=1&pp=15

This lets you spit out any shading node into a speerate image from one render.

The harder part is linking lights to particular materials that feed into ctrl_buffers. I am not sure how to do thst - especially with Mental Ray.

Also this shader works with Maya. I don't know if it will work with Max.

Simon

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