Friday, September 4, 2009

Physical Sun and Sky in Softimage

If you have used the Physical Sun and Sky in Maya and Softimage, you may have noticed that in Softimage the setup is halfway done. Only the sky is created, no lens shader is used and the Sun is using a soft light shader instead of the physical sun shader.

If you want to have a setup similar to Maya you have to connect everything manually. I got tired of connecting all the shaders manually so I have modified the Initialize sky shader script to include all those changes.

Once installed (see Softimage Help on how to install addons) you will have a new entry in the Pass > Edit menu : Initialize Physical Sun/Sky Shader
The Initialize window is similar to the default Initialize Sky Shader window. Choose your pass and you sun light then click Apply.
The plugin will create the physical Sky shader in the pass environment stack.
It will also add a photgraphic Exposure shader in the pass lens stack and set the pass lens stack mode to Add After Camera Lens Shaders.
And most importantly it will add a Physical Sun shader in the light shader, replacing the default soft light shader.

Now you have all the proper shaders to create physically accurate renders.
But some of the default values in these shaders are not correct, the plugin will take care of adjusting them correctly.

In the Physical Sun shader you will notice that most properties are controlled by an expression, exactly like in Maya.

You can edit the shadow softness and shadow samples of the Sun in this shader.

Most of the values in this shader need to match the value of the Physical Sky shader exactly. Connecting these values with expression is the easiest way to keep these values linked.

In the Physical Sky shader, the multiplier values is set to 1 instead of 0.1 and the rgb Unit Convertion is set to 0.318

As mentioned in the Sun and Sky Mental Ray documentation:
When setting the rgb Unit Convertion values to 0.318, the final rendered pixels in the image are true photmetric luminance values in candela per square meter.

These true luminance values then fit perfectly as input to the photographic tone mapper.

For the Photographic Exposure shader, the plugin sets the F-Stop Number to 16 and the c/m2 Factor to 1.
Setting the c/m2 Factor to 1 is important to stay in true photographic mode. 
These setting represent the Sunny 16 rule in photography. As discussed in the Physical Exposure Mental Ray documentation.

To adjust the brightness of the image you can simply adjust the Shutter Time and the F-Stop.

Note that the gamma value is set to 2.2. It is possible to work in linear workflow in softimage, but I decided to keep the values to the Mental Ray default.

I will discuss linear workflow using the Physical Sun and Sky in a future post ... so stay tuned.

Finally the plugin sets 2 more things: it enables the Final Gathering and set the Ambiance Color to Black. (Don't forget to set the Final Gathering for the Region Render as the plugin do not set it) 

With this setup you will have the exact same setup as Maya ... If you downloaded the Maya modification script provided in the previous post and you create a physical sun and sky setup using the Photographic exposure.

Here are renders done in Maya 2010 and Softimage 7.5. Both renders are using the default Physical Sun and Sky settings mentioned in this post and mia_materials (architectural shader).

Maya 2010

Softimage 7.5

As you can see the result is similar in both application.

I hope you like this plugin.


  1. cool nice job man... here is something that might intrest you

  2. thanks a lot!

    note: if you try to pick a light-source and apply afterwards your script crashes... anyway, without choosing a light-source the script works fine.

    (maybe for an update)


  3. Thanks for the bug report Robert. I did't think to test this since I didn't modified the original script in the pick light section... I will look into it.

  4. np, glad to be of service ;-)


  5. Hello,
    First of all thank you for providing this addon :)
    I have a small Bug Report.
    In Softimage 2010(64bit-windows) the Lens Shader isn´t added to the Camera automatically.


  6. I have tested it in Softimage 2010 32 bit and it works fine. I don't have access to a 64 bit machine at the moment so I can't test the 64 bit version unfortunately. But I don't see why it should not work.

    Also the lens shader is added to the pass lens shader stack not to the camera lens shader stack. This way all the camera will have the lens shader.

  7. Hello again,

    I´m sorry Sylvain, my fault! Working fine now, just checked the camera lens shader stack.

    Thanks again

  8. thanx a lot man!

    i just would like to understand better if i must change the multiplier value on physical sky to 0.1 or keep it on 1? i really didnt understand that!
    the same about the RGB values...

  9. Anyway its a simple and fantastic addon!

  10. Keep the multiplier at 1 and the rgb unit convertion at 0.318 to stay in true photographic values. I prefer this personally because even though you need to set huge value in your light intensity, they make sense (once you get used to it)

    When you are in that mode, you know that a light representing a 600Watt light bulb (around 80 000 if I remember correctly) will always react correctly. Let's say you want to create a day time and a night time render of the same scene.

    Like in real life you will adjust you camera to the appropriate fstop,iso, etc, the difference will be the sun being there or not ... the 60 watt light will be the same value in both setups. In the day time scene the light will not create that much light, but in night it will light up the whole room.

    I hope this makes sense

  11. I have the same problem with picking a light, XSI 7,01 Win 64, scripy crashes too :(

  12. make sure to get the updated version. Follow the link on this post.

    I thought I updated the download link in this post... but I didn`t.

    I fixed the download link in this post now

  13. Great plugin!
    I had to do a scene with sun & sky and photographic exposure and this tool is a real time-saver!

  14. Great Addon, thanks a lot !
    As the "visibility distance" in mia_physical_sky shader is a VOLUME effect, it doesnt work when
    using your script. Thats because your script adds
    the mia_physical_sky shader to the enviroment,
    not to volume shaders list.

    so if u want to use the "visibility distance"
    feature, u have to connect the shader manualy
    to the volume shader list.

  15. lol...I was looking for infos about how using physical sky with Softimage...Of course, it brought me on your tha man Kobayashy!!

  16. Great Addon! Thanks :)
    I use to work with the physical sun & sky with 0.03 as intensity value. your true photographic values seems to be accurate and natural. I have only one problem, the sss compound dosen't work correctly with this settings. It gives a black light map...
    Any suggestions??

  17. great work!!! I always be asking myself why physical sun and sky just doesn´t work like in maya, with all linked and the parameters set right, or at least working acceptable and the light with the physical thanks a lot!!!!!

  18. I second Hakim Harrouche`s comment it gives a black light too for the sss compound

  19. I unfortunately never used the SSS compound and I have no experience with skin shaders and sss, so I am afraid I can't help you much.

    Maybe the compound is clamping value in the 0-1 range? that would be my first guess

  20. From 3ds Max Area site: "Also, turn off Screen (Soft) Compositing Of Layers, also on the Advanced Options rollout; otherwise the output of the SSS shaders is clamped to a low dynamic range and will appear to render black.” I just tried this, and it worked for XSI.

  21. Also, from the same post: "To use a mental ray fast SSS material together with the high-dynamic range Sun & Sky solution, be sure to turn on Scatter Indirect Illumination on the material’s Advanced Options rollout so that the material can scatter the skylight, which is considered indirect." I'm using SkinSSS, which doesn't have this check box, so I can't test it. Hope this info isn't too late. ;-)

  22. Hi Friend

    your tool is pretty useful for me. the only problem that I got is that the constant material i use gets dark. I mean I have used a 100% pure white constant material but after applying your S&S it becomes 100% black!



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