View Full Version : Compositing .rpf and elements (diffuse, specular, etc)

Brian Harp
06 June 2003, 11:34 PM
Hope someone can help me to understand this and hopefully I can explain my self what I’m trying to do and hope I'm in the right forum.

I’m trying to learn a real world example of how you would mix the .rpf files and the “Render to Elements” option in 3D Studio Max. Any steps on how to mix these or IF you’re suppose to.

For example, I want to glow specific objects and materials using object and material id’s in the .rpf files In Combustion AND have the control of changing the diffuse, specular, reflection and atmosphere in that scene while having the same control of a .rpf file. Can I do this, this the right process everyone else does?

I would like to have the same control of my “Rendered to Elements” option, such as atmosphere, diffuse, specular, z-depth, and so on as I do for the .rpf files. I know with these .rpf files you have incredible control of that image and the information in it. In Combustion I can use these .rpf files to extract a G-Buffer Object ID or Material ID, and along with it, know where these objects are placed in 3D space (Z-Depth).

I’m trying to understand, if I have a diffuse channel and a specular channel (rendered to elements images), how do you extract the .rpf information out of it and how would the layers be set up in Combustion to work with all the same control as an .rpf.

What are the correct steps to take in creating something like this with the most control? For example, how can you use z-depth information in the diffuse or specular channels of an image in Combustion like you normally would with a .rpf file?

Does anyone have any real world examples on how a 3D compositor and 3D animator approach something like this?
I just want total control of all channels (diffuse, specular, reflection, atmosphere, zi-depth etc) and the object id and material ID's (.rpf)

Hope I explained it clearly enough,

Thank You for your help,

06 June 2003, 09:00 AM
To be honest Brian.

I have not seen anyone mix RPF with render elements. They either use one or the other.

From my experience if I used an RPF to replace a texture on an object, I would use the paint module to paint the different colour atmospheres that would have been generated by the new material.

Trying to superimpose a render element on top of an image that already has this element rendered in the RPF will double the RGB values in those areas which could cause additional problems.

Like I said, this is what I have seen...



Brian Harp
06 June 2003, 04:41 PM
Thanks Grant,

Here are more details on what I'm trying to do.

We have a 3D hallway with columns on each side created in Max. Down the middle of the hallway are several electrical arcs and pulses also created in Max. We want to be able to have the POV move from behind the columns while looking at the arcs and pulses, then move into the hallway for a full view of them. Finally, we will composite this footage in combustion and want to have control over the following:

We want to be able to separately control the glows and effects on each of the arcs and pulses. We also want to control qualities of the hallway imagery such as specular, diffuse and atmospheres. And we want to do with as little rendering as possible.

So, here's the issue:

With RPF, we can easily do most of the above by rendering the hallway as an RPF stream, then the arcs and pulses as another RPF stream, then using the Z-buffer and material/object ids to get the effects described above in the composite. The arcs and pulses layers can be composited into the RPF hallway background using the Z-buffer and will be behind the columns at the first of the shot, then in front at the end...just as we want them. And the material/object ids can be used to separately effect the arcs and pulses.

However, with RPF, it seems we don't have control over items such as atmospheres, reflections, specular, etc. that we get with Render Elements...which is vital to the look of the hallway.

So, the basic question is how do you combine the qualities of each of these image types for compositing? Can you use the Z-Depth information in Render Elements to have the matte effect you get from RPF (e.g. - the arcs and pulses behind/in front of the columns)? Or do you have to do a separate matte/shadow pass if you're using the Render Elements approach?

Or can you combine certain Render Elements with the RPF layer of the hallway to control the specular, atmosphere, etc. qualities?

Or are we SOL?

Thanks again for the help,

06 June 2003, 05:28 PM
I am going to have a stab in the dark here. The elements can be rendered out with an alpha channel or you could use the luminace of the channel to create a selection of the area that you wish to affect and once the selection is applied you could then use the operators in combustion to tweek the settings.

It's a long shot but worth a try.



Brian Harp
06 June 2003, 03:48 PM
Thanks Grant for your help, I'll experiment around.


07 July 2003, 02:28 PM
Hello again Brian:

I tried this yesterday again, and i found a way to use render elements and rpf,with the limitation that you cannot apply 3d post filters. Basically you render one RPF with the object,material,zbuffer info and the render elements in tga/similar format(but be carefull, as i think there is a kind of bug with the alpha channels in 3dsmax and only works for me if i check the premultiply checkbox of tga. For more info on this check this topic: ).

Then open combustion, import all the footage.

Nest the render element layers into a composite.

You cannot apply 3d post filters as they try to read the info required from the same layer footage(please discreet change this!). But you can use show gbuffer,gbuffer extract and so to make alpha channels to use in the nested layers using the COMPOUND CHANNEL SELECTION filter.

If you need help just ask

CGTalk Moderation
01 January 2006, 10:00 AM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.