Clouds in Mental Ray's Physical Sun and Sky (Maya Render Tutorial)

Mental Ray physical sun and sky clouds maya tutorial

In this Maya and Mental Ray tutorial we are going to take a look at an effective and quite simple tecnique to achive realistic clouds in Mental Ray Physical Sun and Sky inside Maya.
If you are interested in realistic exterior renders in Maya and Mental Ray you can't miss this article! 

TYPE: Free maya tutorial

CATEGORY: Rendering Maya, Lighting, Mental Ray

STATUS: Available since 17 Nov 2013



Clouds in Mental Ray Physical Sun and Sky (Maya Render Tutorial)

Exterior windmill render tutorial mental ray maya with clouds


INTRO


There's a lot of mess about how to obtain cloudy skies in Maya renders with Mental Ray Physical Sun and Sky. I read many maya tutorials about that but none really worked properly so I decide to make one myself...hope it will help you in your render creations!

We are going to talk about 3 effective and quite simple methods to achive realistic clouds with Mental Ray renderer and Maya. Anyway in the last method (the third) I make deep explanations because I think it's the most convenient than the other two.   


Let's get started!


WHY I NEED CLOUDY SKIES?

The answer is simple: if you are trying to achive realistic renders you need details, then you have to take care of your skies as much as your ground.
Doing some "cloudy work" can massively enhance your renders...the render below wouldn't be the same without a nice background sky!

 

Windmill render 3d in mental ray with maya clouds



I collected 3 main method to achive cloudy skies, I called them:

1) Internal 
2) 
External

3) Hybrid   



METHOD 1: EXTERNAL CLOUDY SKY (compositing)



The external method is the most popular and simple, just render your exterior scene with the proper alpha or matte channel and composite the final image with your favourite 2D composition software (photoshop, after effects, nuke, ecc..). 


Mental ray sun and Sky with clouds in maya windmill

 External method: the background sky were added in Photoshop 


3d windmill render + maya sky compositing

Windmill 3D model rendered in Maya + Alpha mask + Background sky image


When working with composited external skies you should always keep in mind that the sky does not really exist in your scene, this will make your scene render fast but you won't render reflections and refractions properly..... take care!


Composited sky reflections in mental ray renderComposited sky transparent refractions in mental ray render
 
External Cloudy Sky Method: no reflections and refractions of the sky are rendered



External Method Summary

PROS:  1) Very fast, no additional rendere times because the cloudy sky doesn't really exist in the 3d scene      
        2) Easly customizable, you can easly change the apparence of the sky with external applications        

CONS: 1) No reflections: the sky will not be present in reflected surfaces                                                       
2) No refractions: you won't see the sky in your transparent surfaces                                       
3) No real light contributionthe external sky will not cast or recive light, the overall appearence
of the 
rendered light will not be influenced by the external sky (you will always get a          
clean day 
illumination type even if you put an overcast sky)                                              

 




METHOD 2: INTERNAL CLOUDY SKY (all 3D)


I'm not a big fan of the internal method because its very time consuming: basically we have to create and render the entire environmental sky inside Maya. This "brute force" approach will give you the most realistic result but it will take a lot of time in creating, tuning and rendering. 


Fluid effects sky in maya and mental ray windmill


With the Internal cloudy sky method you won't have problems with reflections and refractions, you will also get realistic illumination and shadows.

To build real 3D clouds you need to use and master dynamic particles or fluid effects, you can find tons of tutorials in the net.
I created and setup a fluid system to obtain clouds, I put about 10 mins in creating and tuning my clouds (not a big time) but my render times gone crazy!!


Windmill render in Maya with no clouds Windmill render in Maya with fluid effects clouds
 
No clouds: render time 2:20 min                                                      Real 3D clouds: render time 21:51 min
 

 

Maya Fluid effects clouds and MR sun and sky reflectionsMaya Fluid effects clouds and MR sun and sky refractions

Internal Cloudy Sky Method: reflections and refractions of the sky are rendered properly


I advise you to use the internal method just if you must (like when you have to render an animated 3d environment with animated clouds).

 



Internal Method Summary
 

PROS:  1) Realistic reflections and refractions                                                            
          2) Physically accurate lighting                                                                                     
3) Animation capabilities                                                                     

CONS:   1) Lots of workYou have to create and tune the entire environment inside Maya. 
        2) High render time volumetric effects are famous for their crazy render times! 


 


METHOD 3: HYBRID/FAST METHOD
 

Mental Ray Clouds in physical sun and sky Maya render


The third method is an hybrid between the internal and the external method: we use an external sky image to drive the internal rendered sky.
By the way this is my favourite method.

                                                 

                          

STEP 1: find a good panoramic sky image 

First of all we need a Cloudy Sky Image (download here for free), HDR images are advised.

 

background environment Cloudy sky HDRI

 

 

STEP 2: create Mental Ray sun and sky system 

 

Open your scene and create the Mental Ray's Sun and Sky from the Maya render settings.

 


Create Mental Ray physical Sun and Sky in Maya



STEP 3: create and connect Maya and Mental Ray nodes


Create these nodes from the Hypershade: 

1) luminance

2) multiplyDivide

3) mib_lookup_spherical

Maya and Mental ray cloudy sun and sky nodes

 

Connect those nodes as follow:

 

1) luminance node to Physical Sky's multipler attribute

Mental Ray clouds luminance node to Physical Sky's 


2) multiplyDivide to Luminance

Mental Ray clouds multiplyDivide node Physical Sky's 


3) mib_lookup_spherical to multiplyDivide's input 1

Mental Ray clouds mib_lookup_spherical node Physical Sky's


4) sky texture file in the mib_lookup_spherical's Texture attribute

Mental Ray clouds mib_lookup_spherical sky texture

 

 

STEP 4:  tune the multiply node 


We need to pump up the values of the multiply node (try some vaues between 2 and 10), high values can generate burned areas and artifacts.

multiply node with mental ray sun and sky clouds

 

 

 

STEP 5: tune sun position 

 
Hybrid cloudy skies can follow sun, just find the prefeer position of the Mental Ray sun node, the sun will be rendered behind the clouds! 


Mental Ray physical sun and sky in Maya: sun position

 

 

STEP 6: experiment other Maya texture nodes


You can use other types of textures to drive physical sun and sky clouds. In this example I use a the maya fractal texture node.

 

Mental Ray physical sun and sky in Maya: connecting fractal node


 Using fractal node will give you lower quality results, but you can easly animate the fractal clouds to create some interesting effects.

 

Mental Ray Physical Sky with fractal clouds in Maya



As expected the hybrid cloudy sky method render Refractions and reflections properly.


Mental Ray Physical Sky fractal clouds reflectionsMental Ray Physical Sky fractal clouds refractions

 

Hybrid Method Summary

 

PROS:   1) Reflections and refractions are 100% working                                                                           
            2) Fast render times                                                                                                                                           
  3) Easly customizable in post-production                                                                                            
                   4) Realistic light contribution                                                                                                               

  CONS:    1) Possibly view dependant artifacts                                                                                                                  
    2) Not 100% physical accurated light contribution.                                                                              
           

 

 

FINAL WORDS

Hope you had fun reading this Maya render tutorial. Feel free to make some questions or leave a feedback!

Antonio

 

 

 

Comments   

 
0 #1 wang zane 2013-10-15 05:13
:D greatfull!!!!
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0 #2 wang zane 2013-10-15 05:14
good sky~~render light l like it .
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0 #3 Marcos Ribeiro 2013-10-15 15:52
Hi Antonio, you managed to achieve a superb environment..pe aceful and colourful place! Nicely done!
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0 #4 Antonio Bosi 2013-10-16 10:04
Hi mates, thanks for the comments!
I start 2 new important works this week, so I think I will be able to publish this tutorial next week! Sorry for the late
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0 #5 Lecra 2013-10-21 18:40
Antonio, sei grandissimo! Bellissimi capolavori!
Il tuo sito e' magnifico.

Saluti dalla Svizzera
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0 #6 Antonio Bosi 2013-10-22 16:41
Quoting Lecra:
Antonio, sei grandissimo! Bellissimi capolavori!
Il tuo sito e' magnifico.

Saluti dalla Svizzera


Grazie per essere passato...tropp i complimenti !! :oops:
Un saluto!
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0 #7 jayzu 2013-12-08 18:35
Another Great Tutorial sir,
you make me want to learn more and more ;-)
Any chance if you can post Tuscan Kitchen or milan's Apartment Tutorials as well?? :-)
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0 #8 Anas 2013-12-29 13:50
Great!

Love your work.
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0 #9 fardeen 2014-01-16 11:53
simply best
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0 #10 BP 2014-01-30 14:19
If you use custom env slot for material with single sample env set to 1 and reflection distance you can also reflect entire sky with all reflections including reflections of 3d mesh... :)
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0 #11 Antonio Bosi 2014-02-05 23:02
Quoting BP:
If you use custom env slot for material with single sample env set to 1 and reflection distance you can also reflect entire sky with all reflections including reflections of 3d mesh... :)


Yes it could be a good addition for the external method, but you need to create a specific spherical/cylin drical map to make it work nicely. Thx for posting ;-)
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0 #12 Chloe 2014-04-03 03:36
Thanks!! It's so helpful, thank you so much
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0 #13 Greshawn 2014-05-11 21:41
Your tutorial showed me how to do this, and ive been trying for hours.

Seriously, Thank you.
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0 #14 Antonio Bosi 2014-05-13 13:57
You are welcome guys, see you in the next tutorial ;-)
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0 #15 Naguip 2014-06-22 23:18
Best tutorial I found in the web, thank you!
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