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Compositing and render passes

Posted on March 4, 2007 2 Comments
Filed under Miscellaneous

I was talking to my friend Mental Ray beta tester Jamie Cardoso lately, and realised that he was rendering his visualisations in single passes.

People who are not involved in rendering might not see the point but you need to think that if it takes you 5 hours to do a render and you realise that the Global illumination is too strong or the colours are too bright then you will have to do few more 5 hours renders until you get it right.

Ok you can always render a small area of your visualisation but if it is not you but the client who is not happy about the render and he needs to see the 8 pictures you have been asked to do every time you submit stuff for approval, then you are in real trouble.

Max and Combustion offer a great way to work in passes but you need to learn combustion and that can be really daunting task. Combustion to me is a bit like the Zbrush of compositing. Great when you know it, horrible when you open it for the first time. Well that’s when you compare it to After Effect, Shake is just as confusing.

combustion.jpg

So what does this leaves you with? Cebas PSD Manager is only $172 and allows you to export your passes straight into Photoshop. Each pass goes into the correct transfer mode.

Unlike Combustion, working on videos would be a real pain. Now there is an other way and that one doesn’t requires any plugins. Mental Ray!

By default mental ray allows you to render passes but the problem is, how do you transfer them into photoshop? I didn’t actually read the mental ray manual since I am not too keen on that rendering engine so I looked for answers elsewhere and found them in the Max to Combustion workflow. Here is how you do it:

The Background layer uses the Normal transfer mode

The Diffuse layer is directly above the Background layer, it is composited using the Normal transfer mode.

The Specular layer is composited using the Add transfer mode. The Self-Illumination, Refraction, and Reflection render element layers are also composited using the Add transfer mode.

The Shadow layer is composited above the Specular layer to dim color in the shadowed areas. By default, the Shadow layer uses Normal transfer mode because its alpha channel controls how much the black and white shadows dim the Specular and Diffuse layers beneath it in the stacking order.

For the composite to match the 3ds Max scene, the Shadow layer must be below the Reflection, Refraction, and Self-Illumination layers. Otherwise, these three layers would also be dimmed.

If the composite has an Atmosphere layer, the layer appears above the Self-Illumination layer. The Atmosphere layer must be composited over all the other layers that are turned on. The Atmosphere layer uses the Normal transfer mode.

By default, the Alpha layer is turned off because it is not required, but it is very useful for compositing additional layers. The Z Depth and Blend render elements are also not required for a composite, so the layers are turned off in the composite when these elements are rendered in 3ds Max.”

Autodesk owns the copyrights of the extract above, I hope they won’t give me any problem. Come on guys I am making your softwares more popular!

The entire content is in the Combustion manual, in the last chapter called:

Combustion and 3dsmax>using render elements>Transfer modes and stacking order.

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