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c-r-u-x
07-10-2012, 11:59 AM
Hey everyone. I'm approaching full-on multipass compositing for the very first time and while I thought everything about it should be pretty much self-evident I have to acknowledge that I don't really know what the heck I'm doing.

The shot I'm working on is a render from Vue - maybe you can help me and tell me in what order and especially with which merge operations I need to approach these layers in order to assemble something that looks like the beauty pass.

Here are the passes I have:

http://www.c-r-u-x.de/IRTF/multipass.png
CLICK HERE FOR FULL SIZE (http://www.c-r-u-x.de/IRTF/multipass.png)

And here is what they should look like (i.e. the beauty pass):

http://www.c-r-u-x.de/IRTF/beauty.png
CLICK HERE FOR FULL SIZE (http://www.c-r-u-x.de/IRTF/beauty.png)

Don't mind the merge operations in the screenshot - I started playing around wildly with some of them, so stuff like the "hypot" operation on the indirect lighting pass stems from that desperation. :shrug: (Not that I know what merge operations to actually use but I'm pretty sure it's not "hypot"... or is it? :rolleyes: )

Cheers,
Chris

earlyworm
07-10-2012, 02:57 PM
Not familiar with Vue's multi-pass. But judging from the documentation http://www.scribd.com/doc/88989444/209/G-Buffer-and-Multi-Pass-Options it doesn't look too different from any other renderer...

Diffuse + Specular + Ambient + Indirect Lighting + Atmospheric Gain + Atmospheric Filter + Background

(where + is a Plus node inside Nuke)

As far as Diffuse Lighting and Specular Lighting go. I think you'd need to output Material Colour as well. Then you would multiply Diffuse Lighting with Material Colour and you'd multiply Specular Lighting with Material Colour. The result of doing this would give you the same result as the Diffuse and Specular outputs.

The Shadows pass is already included in your Diffuse pass. Having the separate shadows pass allows you to attenuate the shadows in the Diffuse Pass (ie. you can lighten or darken the shadows).

Hope that helps.

c-r-u-x
07-10-2012, 04:11 PM
Not familiar with Vue's multi-pass. But judging from the documentation http://www.scribd.com/doc/88989444/209/G-Buffer-and-Multi-Pass-Options it doesn't look too different from any other renderer...

Diffuse + Specular + Ambient + Indirect Lighting + Atmospheric Gain + Atmospheric Filter + Background

(where + is a Plus node inside Nuke)

Whoa... you just blew my mind. I always thought Plus and Merge (Plus) are the same thing... turns out they're not. But what exactly is the difference?

Now here is the image assembled like you suggested. But the Atmosphere Filter doesn't work with a Plus - it turns everything White (as you can maybe see in the thumbnail, it's mostly white). The result looks a lot closer to the beauty pass but still not quite there.

It doesn't look like the shadows are actually already in there.

Here it is without the shadows:
http://www.c-r-u-x.de/IRTF/noshadows.png
CLICK HERE FOR FULL SIZE (http://www.c-r-u-x.de/IRTF/noshadows.png)

Here I multiplied the shadows in. The foreground looks better now but the background is too dark. Maybe I'll have to plus the Atmosphere Gain after the Shadow multiplication.
http://www.c-r-u-x.de/IRTF/pluseverything.png
CLICK HERE FOR FULL SIZE (http://www.c-r-u-x.de/IRTF/pluseverything.png)

Still not looking like the beauty pass but getting closer. This is what it'll have to look like:
http://www.c-r-u-x.de/IRTF/beautypass.png
CLICK HERE FOR FULL SIZE (http://www.c-r-u-x.de/IRTF/beautypass.png)

I'm still not sure what to do with the Atmosphere Filter though...

And can you please explain to me the difference between the Plus operation in the Merge node and the standalone Plus node?

earlyworm
07-10-2012, 05:51 PM
If you are going to multiply the shadows in, I'd probably do it after the diffuse and specular outputs have been added together and before you add the ambient and atmospheric outputs - neither of which should be affected by direct shadowing information. The documentation suggests that the background should be added with the rest of the outputs but if your happy with using an over go with it.

The Plus node is just a Merge node set to Plus. If you want to test this, merge two constant nodes with a value of 0.18 together and see if the pixel values add up correctly to 0.36.

c-r-u-x
07-11-2012, 11:10 AM
So now I changed the order and some of the merge operations and I'm getting fairly close but two things are still odd. Firstly the ambient (i.e. the teal cracks in the rocks) look brighter and have a different colour than in the beauty pass and secondly the entire image is more crisp than in the beauty pass.

Maybe both of these are caused by the Atmosphere pass not being composited properly yet - but I can't quite figure out what this description in the documentation (http://www.scribd.com/doc/88989444/209/G-Buffer-and-Multi-Pass-Options) is supposed to mean for me:



Atmosphere filter: this component, together with the Atmosphere gain component containsthe effects of the atmosphere on the rendering. It is necessary to hold this information on twolayers, because of a limitation in the Photoshop layer handling (no true additive mode); this component is saved as a normal (i.e. additive) layer in Photoshop documents.

Atmosphere gain: this is the second half of the atmosphere effect; it is saved as a product layer in Photoshop documents.


Atmosphere filter is supposedly an additive layer but if I plus it, everything turns white. Atmosphere Gain is supposedly a 'product layer' but if I multiply it, everything turns really dark. If I multiply Filter and plus Gain, I get pretty close to the beauty pass - but, as I mentioned before, not quite.

This is how I assembled the passes:
http://www.c-r-u-x.de/IRTF/multicomp03.png
CLICK HERE FOR FULL SIZE (http://www.c-r-u-x.de/IRTF/multicomp03.png)

This is how this multipass comp looks:
http://www.c-r-u-x.de/IRTF/multipass03.png
CLICK HERE FOR FULL SIZE (http://www.c-r-u-x.de/IRTF/multipass03.png)

This is the beauty pass:
http://www.c-r-u-x.de/IRTF/beautypass03.png
CLICK HERE FOR FULL SIZE (http://www.c-r-u-x.de/IRTF/beautypass03.png)

If you open up the two images in different tabs and switch between them you can see the difference.

Any idea what to do with the atmosphere layers to get the ambient colour right and maybe have it soften the image so it looks like the beauty pass? Or is Vue cheating and doing stuff in the beauty pass that isn't in the multipasses?

I looked again at the postprocessing pass for something like that but it's just empty.

Thanks already for all your help!

Chris

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