Isolating Reflection in Maya

#1

Hi All,
I’ve asked this question a couple of times and didn’t get any reply. I’ve searched all over the net and no answers.

I would like to know how to isolate a reflection pass from the floor. I have a chair placed on a very reflective floor and would like to extract the chair reflections from the floor. I’ve tried a “Use Background Shader” but it didn’t work.

I’m wondering is this is even possible in Maya. I’ve tried it in maya 2009, 2012, and 2015 still no success.

Pls can someone save a life?

Thanks

Jon

#2

Hi Jon,

Hope you are doing well!

for this particular pass, you can use selection pass.

  1. add some constant colors to the object (Chair).
  2. add secondary pass (AOV), Reflection.
  3. You can extract it in Composting software or photo editing software.
    (I guess you are using Mental ray as a renderer, But this can be done in any Render engine)

http://forums.cgsociety.org/attachment.php?attachmentid=180252&stc=1
Hope this will answer your issue.

Good luck.

Thanks
Sagar

#3

Hi Karsa,
From the image u attached, seems you did what I want to do. However, I don’t seem to understand the process you wrote, and I’m not a pro like you.

  1. What is a “selection pass?”
  2. Why do I have to add a constant color beside the chair color (wood color)
  3. Secondary pass? What is AOV?

Yes, I’m using Mental Ray. I’d do the comp in AE though.
I’d be extremely grateful if you could patiently help me get this process as clear as possible.

Hope to hearing from you again.

Thanks

Jon.

#4

Hi Jon,

First let me answer your Questions.

1. What is a “selection pass?”
2. Why do I have to add a constant color beside the chair color (wood color)
Basically, if you want to select something from scene in Editing software to change the color or pump up the brightness, you have to render 1 Pass in constant R\G\B color. all image editing or composting software’s can select R\G\B colors and make “selection” of it for editing, thats why it is called selection pass or mat pass.

3. Secondary pass? What is AOV?
Maya or any renderer can output additional data (specular highlights, reflections, shadows, etc.) into separate image files, called Secondary pass or AOV (Arbitrary Output Variables)
Secondary passes are useful for compositing. It can be more efficient to adjust certain effects in compositing (such as tweaking specularity) than rendering the image over and over again.

Now, The Process for Above pass is very simple.

  1. Create a render layer or make copy of your file, name it “Reflection Mat”.
  2. select your specific Object you want to select in Compositng.
  3. assign Lambert shader to it.
  4. change the Diffuse color to R (1,0,0)
  5. make difusse 1.0 (0.8 by default)
  6. Render your scene with same lighting setup.
  7. if you are using Final gather, make your chair’s cast FG off. in shape nodes Metal ray section
  8. Then add contribution pass in in render layer by right click
  9. add reflection pass from Render setting> Passes
  10. you have to render 2-3 times to get the same result like above example.
    11.floor should be black and only chair should be visible in reflection pass image

May be you can test it with Planes and sphere first.

Hope I have explained it!
Good luck

Thanks
Sagar

#5

Hi karsa,
I know about the Matt., and I’d go ahead and follow your steps and try this this out. If I’m lost somewhere, could it be possible I send you the scene to check?
And by the way, while rendering passes, must I turn on Maya’s default light ON? The reason I ask is, if I turn it off, my renders will become dark and sometimes completely black. Even when I have a directional light in the scene. Though I normally turn the intensity down and rely on my IBL.

Thanks.

Jon

#6

Moving this question to the correct forum

#7

Which Forum did you move it to, pls!
Thanks

#8

CGTalk > General Techniques > Lighting and Shaders > Isolating Reflection in Maya

Lighting challenge forum are for mini-lighting challenge. Please take some time to read the rules of the forum and subforum before posting.

#9

Hi karsa
Is there a way i can send you the file to check my setup?
I still did not get the reflection I want like the one u did.
can I email it to you?
I can’t attach it here.

Tks

Jon

First let me answer your Questions.

1. What is a “selection pass?”
2. Why do I have to add a constant color beside the chair color (wood color)
Basically, if you want to select something from scene in Editing software to change the color or pump up the brightness, you have to render 1 Pass in constant R\G\B color. all image editing or composting software’s can select R\G\B colors and make “selection” of it for editing, thats why it is called selection pass or mat pass.

3. Secondary pass? What is AOV?
Maya or any renderer can output additional data (specular highlights, reflections, shadows, etc.) into separate image files, called Secondary pass or AOV (Arbitrary Output Variables)
Secondary passes are useful for compositing. It can be more efficient to adjust certain effects in compositing (such as tweaking specularity) than rendering the image over and over again.

Now, The Process for Above pass is very simple.

  1. Create a render layer or make copy of your file, name it “Reflection Mat”.
  2. select your specific Object you want to select in Compositng.
  3. assign Lambert shader to it.
  4. change the Diffuse color to R (1,0,0)
  5. make difusse 1.0 (0.8 by default)
  6. Render your scene with same lighting setup.
  7. if you are using Final gather, make your chair’s cast FG off. in shape nodes Metal ray section
  8. Then add contribution pass in in render layer by right click
  9. add reflection pass from Render setting> Passes
  10. you have to render 2-3 times to get the same result like above example.
    11.floor should be black and only chair should be visible in reflection pass image

May be you can test it with Planes and sphere first.

Hope I have explained it!
Good luck

Thanks
Sagar[/QUOTE]