Render passes

[J_Bug]

Could someone with experience in this area help by describing any workarounds for deriving the following render passes from VRay?

Color/Diffuse
Direct light
Shadow
Reflection/Specular
Refraction
GI

Thanks in advance,
--Jon

[percydaman]

Well for me it usually involves alot of material and lighting changes. Make everything white mat, lose all reflections, turn off all direct lights, set environment to white and render. Theres your ambient occl pass.

I dont do it alot so I dont recall exactly what I do for each pass, just thats a pain in the butt to do it. When I DO need separate passes for a fairly complex scene, I find I usually resave the scene so that when I start changing materials and settings I dont forget where all my mats go.

Check out this greeat tut by seraph. Its pretty damn good

http://www.seraph3d.com/composite_main.htm

He just needs to add a tut on doing a reflection pass

[J_Bug]

Hey thanks soooo much this is great information

Much thanks to Seraph likewise

--Jon

[cocolas]

yeah, thanks much, percydaman!!!..as well as Seraph.....great work!



paul.

[Seraph135]

No problem guys. I'm glad you found them valuable. Reflection pass is do-able. I'll try to put something together in the next week or so.

Tim J

[J_Bug]

Seraph135:

Wow Very cool

I have some other links on this subject at home that I'll post here for all who haven't seen them. They aren't as in depth as yours but very interesting non-the-less.

One question if you don't mind...

Are these techniques primarily used for composition into a live action plate or are they also as useful to you for a complete CG environment.

Thanks again,
--Jon

[percydaman]

They are also useful for a completely cg environment as you can tweak any given pass for contrast and so on. Makes pipelines quicker as you dont have to rerender entire scene again.

[cocolas]

Seraph135:

Wow Very cool

I have some other links on this subject at home that I'll post here for all who haven't seen them. They aren't as in depth as yours but very interesting non-the-less.

One question if you don't mind...

Are these techniques primarily used for composition into a live action plate or are they also as useful to you for a complete CG environment.

Thanks again,
--Jon

Jon, it would be really cool if you could post those links you have, as well....

thanks!

paul.

[DP]

we find that often we need to isolate a material in the scene in addtion to the alpha of the whole scene, so we made a dirty script to alter that material to a 100% self illumnated white, and all other materials black...then we just stick that in the render queue afterwards.

I say its dirty, because the target material needs to be a specific name, it cant cope with shapes for some reason, the material needs to 1st in the editor, and it doesnt edit the vray renderer because we dont know the scripting needed for vray's renderer. But 10 secs of manually doing those extra bits means that we can alpha out materials with ease and still have them obscurred by geometry, thus making a good mask for windows etc. That combined with a simple material means we can also isolate the enviroment from reflections, but still retain reflected geometry.

But it would be nice if vray just had passes

[J_Bug]

cocolas:
It's strange, I went home and immediately posted the link but it's not here now. IE crashed on me a few times but I thought it was after the post I'll have to post it tonight.

DP:
Thanks for this explanation it's very informative. I'm seeing now that it's much easier than I imagined. I guess I'll just have to use these techniques on a few projects to get the hang of them and then it'll be like writing my own name I wish I had a chance to use them in my day to day work. I even went to a two week film camp where we comped CG into live plates with MAX (I had to use the scanline and skylight instead of VRay )but they didn't teach us these techniques)

--Jon

[J_Bug]

here ya go

http://www.andrew-whitehurst.net/tutorials.html

--Jon

[cocolas]

nice!!
thanks jon

paul.

[richard_rosenman]

Hi Jon;

Here are some of the techniques I use.

Generally, every commercial we do is split up into 'x' number of layers so that the compositor will have the most amount of control over it. We don't go overboard and render out 25 layers (although it has come to that for some jobs) but we usually do end up with around 4 - 6 layers per scene.

The first layer I always render is the background. This is, of course, with any character/subjects excluded from the scene although if the character/subject will not be moving, I will sometimes make it 'not visible to camera' but keep it in the scene so that the area in which the character/subject makes contact with the floor/ground is affected and therefore darkened due to the GI shadows.

The second layer is always the character/subject. This is always rendered with the exact same lighting set-up as the background was rendered with (you obviously want the character to match the background lighting) and sometimes I make the background 'not visible to camera' so that it's color will also influence the character. Sometimes I also use the rendered background map as a light-map in conjunction with my lighting rig.

Third layer I usually do is the shadow pass which I do the 'old-school' way and break into two layers. The first layer is everything assigned a white material, with only the main light casting a shadow. The character/subject is 'not visible to camera' so that the shadow it casts is rendered, but it isn't. This I usually call 'char_shadow'. Then I hide the character and re-render the same scene which I call 'char_noshadow'. I then bring the two layers into any compositing program and do a difference pass to reveal only the shadow. Difference passes are great and they can be used for a wide variety of things, including reflection passes, etc.

The fourth layer I often render is the reflection pass. This is simply hiding everything except the reflective object, making it fully reflective (perhaps with a falloff effect if it is required) and then rendering it out. In the compositing software, I can then comp it any which way I want. (screen/multiply/overlay/etc.)

The fifth (and sometime redundant) layer is the spec pass. This is only done when I really need one (ie. for wet characters/subjects that need a really strong highlight) or when I need the specularity to be of a different color and/or treatment. This is as simple as assigning a black, matte material to the character/subject, with a very high specularity and rendering this out, to be composited as a screened layer. Sometimes I do a seperate spec pass for eye highlights like I did for "Plumber".

Ummm.....that's really about it. you can get far more technical and break the above mentioned layers into many more sub-layers of even finer control but often the above is enough for me. Of course, every project is different and requires different layers/effects but they all follow these basic principles.

I think I wrote another post a long time ago (a much longer one) in which I go much more in depth on how I break up my layers specifically for character animation. You might want to try a search for this as it shouldn't be too hard to find since I don't post that much or that often.

Anyways, hope this helps. If you have any questions, don't hesitate to ask.

-Richard

[J_Bug]

Richard:

Thanks, this really helps with understanding the workflow. I found the other post you mentioned. Wow don't know how I missed this great information, I was probably surfing your site after seeing the start of the post and forgot to check back. Here is a link for all who haven’t viewed it either.

http://www.chaoticdimension.com/foru...266&highlight=

Well, I've got some reading and test scene creation to work on so I'll be back soon

Thanks so much to all who contributed to this post. I think this is a very significant point in my learning true professional techniques to approaching CGI.

--Jon

[OmeN]

Brilliant post.
Im just about to embark on my first project being rendered with vray.
Ofcourse I've composited scene's before however im doing my homework first if there is anything special i can do.