Linear Workflow dedicated website

Master Zap have launched a site on linear workflow http://www.lysator.liu.se/~zap/lwf/ There is nothing much on there at the moment but it will surely gets filled with a good amount of great information in the near futur.

I thought it was worth talking about that site, you should check it out regularly...I know I will.

Physical Sun And Sky addon Update

I have updated the Physical Sun and Sky plugin for Softimage. This update fix the bug where if you pick a light source instead of creating a new one the script would crash.

You can grab the version 1.1 here

Thanks to Robert for finding this bug.

Softimage 2010 demo

The Softimage 2010 version is finally out. You can download the demo on the Autodesk web site.
http://usa.autodesk.com/adsk/servlet/pc/index?siteID=123112&id=13572885

I was happy to see that it comes with Mental Ray version 3.7.55 ... Maya uses version 3.7.53.
It is nice that both software are finally using the same version. Softimage was always one Mental Ray version behind.

But at first glance there doesn't seem to be a whole lot of 3.7.5 features implemented in Softimage 2010. I will investigate more.  The nicest feature I can think that would be usefull is the map data which can be used to save particle information.  This could prove useful to pass particles system from Maya to Softimage. I will definitely look into that.

Linear Workflow in Softimage

Softimage have great options to work in a Linear Workflow (LWF), in this post I will explain how to setup Softimage Preferences to work with the Physical Sun and Sky setup

By default Softimage is setup to render in a non-physical way, when using a Physical setup you need to change these option to make sure that all you color swatches and textures are linearized.

Here is the scene setup.

The diffuse value of the green sphere.


The texture connected in the diffuse slot of the sphere to the right.








In the preferences, the Color profile for the texture is set to Linear and the Color Management is not active. Rendering the scene with a gamma of 2.2 in the Photographic Exposure shader give you this.

Everything is washed out!  The typical non linear render. 

Notice how the green of the sphere doesn't match the color swatch of the shader and how the texture is washed out.

We can fix this quite easily.

In the Preferences, in the Rendering section, under the Image tab, set the Color Profile to Automatic.

The automatic Mode will linearize sRGB image and keep high dynamic range image linear. You can also change this in the each image clip.

You will also need to enable the Color Management in the Display section of the Preferences

In the Photographic Exposure shader you will need to set the gamma to 1.0. Since Softimage is now in charge of the gamma, you can remove the gamma from the exposure shader.

Now when you render you will get a a better result in the UI.

You might have noticed that the green color swatch in the shader now match the render result. This is exactly what we want, now the color you set in your swatch match the render... how wonderful!

But if you render the current pass to disk in a 8 bit format, when you look at the renders everything is darker...

This is because Softimage Color Management is only applied in the UI, when you render to disk the gamma is not applied to the output. This is quite useful when doing compositing because you are not dealing with baked-in gamma.  All you need to do is apply a 2.2 gamma at the end to get the proper result.

In a comment of my previous post, Edin pointed out that it is possible to apply the gamma when rendering out to disk. In the pass option, locate the Pass Gamma Correction section and enable the Apply Display Gamma Correction

You end up with this result.

For some reason the gamma not applied to the environment ... this is not a big deal because you will rarely use the physical sky as your background. But it is something to keep in mind when using this pass option.

I hope this little tutorial was helpful. Feel free to point out any errors or omission in this post ... or even suggest alternative methods.

Finally, here are 2 links that you might find useful. They discuss LWF in Softimage and in Vray
http://community.softimage.com/forum/autodesk-softimage/rendering/softimage-gamma/page-1/
http://www.aversis.be/tutorials/vray/essential_gamma_01.htm

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.

Download the addon here

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.

mia exposure photographic AE template

Maya doesn't ship with an AETemplate for the mia_exposure_photographic so you end up with an Attribute Editor showing raw attribute without any logic.

If you read the Mental Ray documentation on the photographic exposure shader you can see that if the film_iso attribute is set to zero then the shader is in Arbitrary mode, then many attributes are ignored, like the camera_shutter and f_number for example.

I have created this AETemplate to add some logic in the Attribute Editor of the shader. The Template also group attributes logically and hides the more advance attributes.

Download the AETemplate here (View the readme.txt for installation)

EDIT (sept 04, 2009): I have update the script to force the automatic photon energy attributes of the physical sun shader to ON. This is usefull if you want to shoot photons from the physical sun.

It is also sugested in the documentation to set the rgb_unit_convertion value of the physical sun and sky to 0.318 when using the physical tonemapper.

To help you acheive this, you can download a modified render global script created by David Jonhson that will promp you with a choice of tonemapper to use when creating a physical sun/sky setup and set the appropriate rgb_unit_conversion value.

>You can visit David site to download the script.

I have created a slightly modified version of David script.

David use a gamma value of 1 in both the simple and physical tonemapper and set the miDefaultFramebuffer at 0.45.

I prefer using a gamma value of 2.2 in both shader and leave the miDefaultFramebuffer value at 1.

This is purely a personal choice. I prefer controling the gamma in the tonemapper to avoid confusion.

My script also uses a promp dialog instead of a small window.

Again this is purely personal. I find this method simpler and more straightforward.

Download my version of the script.

Both method are equaly good in my opinion, you can pick the one you feel more comfortable with.