shaddow pass and Nuke

[nomads]

Hi

I am comping objects onto a back plate in nuke.

What is the preferd way of rendering the shadow pass?

In Nuke I am using a grade node to colour correct the backplate using the shadow pass.

The image from vray comes with an alpha containing shadow information. This affects the back plate. Should I re render without the shadow info in the alpha? And just use the shadow pass info?


Also should you colour correct the shadow on the back plate differently than the shadow on the 3d object?

[svetlozar.draganov]

The best option would be to render two separate passes with and without shadows - this will give you a greater freedom in the compositing stage.
However it would be very helpful for us if you could send us a practical example of your V-Ray/Nuke workflow since there might be a better way to achieve the effect you are looking after.

[nomads]

Hi Svetlozar,

I have put together a simplified work flow and all the files.

https://www.dropbox.com/s/y7js5zwkja...asses.zip?dl=0

My strategy is to do two passes. Beauty and reflections etc in one and the shadow and AO in the second.


Here are a the problems I am noticing.

1/ In nuke I cannot recreate the beauty pass. The reflections are too week.

2/ The shadows are to week. This is probably vray max. I tried to get the shadows from the hdri.

I did no bother with GI because there is noting the bounce back.

I would relay welcome any tips.

[Morbid Angel]

I had a look at your script some notes:

render in two passes - one torus, second torus invisible to camera (only its shadow on the ground)

do not use raw reflection - it has troubles rebuilding back. Use raw lighting + raw gi * diffusefilter + reflection + specular + refraction

use shadow below torus to grade the plate down, you can mix the shadow (direct with ambient occlusion shadow) to create more of occlusion like feel.

[nomads]

On the first pass... Should I include a shadow pass just for the torus?

On the second pass if the shadow is just for the ground I could turn down the samples on the dome light to speed up the render? Apply a little blur.

Also as the shadow is not strong enough from the HDRI dome light should I do a third pass and take the shadow from a VraySun. If so should I split the ground and torus again into two passes?


Reflection. Going back to the VrayReflection has cleared up my reflection problem.

I thought the VrayRawReflection * VrayReflectionFilter was supposed to give you more control.

[svetlozar.draganov]

Please note that the Raw Render Elements are not calculated properly if the corresponding Base Element is not added.
In your case Raw Reflection element is extracted but Reflection one was not - that's why the end result is different.

[Morbid Angel]

you dont need a shadow pass on the torus.

for the ground shadow yes you could do things like that but generally its easier not to mess with the settings

last option is up to you...you also have occlusion to help you in that case