Tutorials for compositing G-buffer channels/elements?

[rpc212]

Hi all,

Just got Combustion 4 and I am wondering about compositing G-buffer channels/elements and tutorials for doing this. I know this will be a huge improvement for how I work as I always want to add more to my renderings, however, I always seem to run out of memory and having the ability to break scenes up and render out layers and then composite them is just going to be awesome.

I need to know how to composite the G-buffer channels/elements properly so I can get this into my workflow ASAP.

The tutorials that come with Combustion don't seem to cover G-buffer channels/elements. Is the workflow exactly like Max's render elements? The G-buffers have always kind of confused me and I have always wished that Vray had render elements just like Max's.

Any books, tutorials, or videos you guys can suggest would be much appreciated!


Thanks,

[percydaman]

have you read the gbuffer info in the help page? Its all pretty straightforward. If your looking at rendering/lighting in layers, Id recommend looking at max 8's scene states, or a 3rd party tool like RPManager. Its essential for keeping your workflow efficient.

Ive been contemplating creating a tutorial on what Ive learned so far on lighting/rendering in layers but frankly not sure if I have the time or energy.

[rpc212]

Yep, read the stuff on the Help Page for G-buffers. Maybe I am over complicating it in my mind. Although, right now, I feel quite confused about what to combine to get the results I want.

Eg. Using add, subtract, multiply ect and how/when to use them with what G-buffer channels to get the desired output. I know some of this is explained in the G-buffer help index, however, it seems not all the combinations are explained. Either that or I don't understand that to explain all the combinations would take up an enormous amount of pages.

Another example is: Having just a simple cube sit on a plane with a plane as a background. How to render this out with the cube as one layer and the planes as another layer. (The cube representing a building, character, or whatever and the planes representing the environment the building, character, or whatever is sitting in/on.) Then combining these to create the final image.

Anyhow any help would be great!

Thanks in advance!

[Adam H. Stewart]

Check out this thread

You could do the cube thing you are talking about within Combustion using a material or OBJECT ID. The material ID would allow you to seperate the elements into two different elements. Of course you would need to go through all your materials or objects to assign the ID first and it might be easier to use the Vray properties and assign an matt with alpha contribution set to -1. There is more then one way to skin a cat I'm afraid. Check out the thread below I was going through the Vray G-buffer puzzle last week:

http://www.chaosgroup.com/forum/phpB...hlight=gbuffer

I have just started using the G-buffer within Vray and I have to say they are an awesome idea not quite yet realized. They are confusing. I really had to ramp up my AE skills to get my head around the concept -i.e. if you put something in multiply mode the black goes away - I think.

In my experience G-buffer seems to be all about adding things together in different overlay modes, screen & Multiply. I have also had to use set matt channel alot to extract an alpha channel for say a shadow layer (set alpha to luminance), or invert to turn the shadow pass from white on black to something more useful.

Of course then you have the show G-buffer and extra G-buffer options within combustion which is a totally different ball of wax. It can get real confusing real quickly, the potential to get lost in RPF files and Vray layers is massive. Sometimes it can be easier to set up your layered passes seperately with materials, this is something I have started to do using scene states but a word or warning - in 7.5 when you revert back to a scene state with save materials, the materials don't always update in the the Material Editor, so you should always do a quick render test that you are editing something active.

Hope my rambling reply helped.


Good Luck

[percydaman]

if you put something in multiply mode the black goes away - I think.

no its opposite. Add makes the black go away, multiply basically makes the white go away.

[cpnichols]

Keep one important thing in mind.

There is no ADD in photoshop.

I know that you are using combustion, but other who may be reading this may need to know.

[Dynedain]

Keep one important thing in mind.

There is no ADD in photoshop.

I know that you are using combustion, but other who may be reading this may need to know.

There is if you do an image calculations instead of trying to do it through a layer. Also, I've heard that CS2 has Add as a layer mode, but I don't have it yet to verify.

[rpc212]

Thanks Adam for your reply. I'll say the G-buffers are confusing.

If anyone has any tutorials or books they could suggest to learn about compositing channels together that would be great!

Did you guys all learn from trial and error? I wish Vray had the render elements just like the scanline with output to Combustion workspace as, it would seem to me, to be alot easier to figure out. Also documentation via Autodesk is already provided with tutorials ect. To me there just doesn't seem to be much info about the Vray G-buffer channels and thus us newbies are really stuck : (.

Be nice if Chaos could put a compositing tut together to show the power of the Vray G-buffer channels in a compositing package and relate it to other popular compositing packages! Personnally, I'd pay money for this.

[Ramsay]

Also, I've heard that CS2 has Add as a layer mode, but I don't have it yet to verify.

Nope, not that I can see anyway

[rpc212]

I guess this will all be easier when Vray 1.4x.xx comes out and it has the Render Elements like Max's along with being able to save the Combustion workspace when rendering! Can't wait for the next release!

[ShaunDon]

In Vlado's tutorial, he's using a "divide" blend to create the mask for the teapot composite... does this go by any other name in compositing software? I can't find any blend mode in combustion that does the same thing. As nifty as the VRayCompTex material is, I don't really want to be compiling all my render passes using max.

[czoog]

In Vlado's tutorial, he's using a "divide" blend to create the mask for the teapot composite... does this go by any other name in compositing software? I can't find any blend mode in combustion that does the same thing. As nifty as the VRayCompTex material is, I don't really want to be compiling all my render passes using max.

There is no "divide" in combustion as far as I know. We use the vray comptex for the divide portion and do the rest in C*

-Z

[panthon]

I guess u don´t want to render all gbuffers out, you won´t need all of them. The ones i usually render out are

Global illumination
Direct illumination
Reflection
Refraction

Actually, I don´t render diffuse because it´s included in the global illumination buffer.

This way, following the help file, u should get an image similar to the straight render, but somehow, i never get exactly the same image...

Once u have them all, i usually render an rpf file with object id information. This way i can add this information to my reflection layer, to adjust the reflection of any particular object without affecting the others.
That´s the theory, but in fact this method is not 100% working...

It would be great if u could select an object, a window glass for example, and change any channel with minor hassle. If u want it to be less reflective, np, change the color, make it less transparent, erase it, remap it, change the texture...

[vasilescu_anton]

Keep one important thing in mind.

There is no ADD in photoshop.

I know that you are using combustion, but other who may be reading this may need to know.

There is ADD in photoshop since version 7 only that is called Linear Dodge so it won't get confused with the one in After Effects which deals with alphas.