Image Based Illumination

Creating image based lighting with the RenderMan Artist Tools 

Introduction  - Creating Image Based Lighting

Here we'll cover the workflow involved in setting up image based lighting with Slim. For more information about image based lighting in general, you'll find a trove of info out on the web. 

Image base lighting

Using IBI

1 -  Open the Tutorial Scene 

For this tutorial, open the scene: 
/mtor/scenes/ibi/ibi.ma

This scene contains a model of a dragon perched upon a rock. We'll light the dragon using image based lighting techniques in conjunction with Slim. By the end of this lesson you should have an understanding of how to create image based lighting effects with Slim.

Hint: To see the subdiv visualization in Maya, you may want to select the dragon and toggle object x-ray:
RenderMan-> Pixar Subdivs-> Toggle Object X-ray

 

The Maya scene.

2 - A Preliminary Render

Your image should look like the "before" image on the right. There are no scene lights, so the geometry is black. The back ground color is set to blue. 

To illuminate this scene we'll use an environment texture, plugged into an environment light. All illumination will come from an image map. This is what image based illumination is all about.   

 No scene lights
 

So let's get started. 

Scene with image based illumination

3 - Create an Environment Light & Shaders

Now we'll create a setup for image based lighting:

1) First we'll start by creating an ensemble. From the palette perform the following operation:

File-> Create Appearance-> Ensemble-> Ensemble

Open the Ensemble by double clicking it in the palette. 

2) Attach an Environment light, by clicking on one of the light connections and selecting "Environment." The environment light's environment map will be used for the image based lighting. (The environment map could be be named "world" and it would affect the entire scene. The environment can be attached directly to objects or plugged into an ensemble to affect specific surfaces. For this example we're attach our environment light to a ensemble.)

3) The third step entails creating a shading model that knows how to generate image based lighting effects from an environment map. Fortunately for us, all of Slim's out-of-box shading models know how to do this. Select the shading model connection and pick "Plastic."

Your ensemble should look like the image on the right.

Create a new Ensemble 
with a Plastic & an Environment Light

4 - Load in the Environment Map

1) Choose an "Environment Map" by opening the file picker () and selecting "rocks_intensity.tif" from the rmantex directory.

Next we must convert the texture. From the texture menu ( ) select: 
Convert-> Convert Textures. 
For this image Slim adds the syntax:
[txmake rmantex/rocks_intensity.tif -envlatl -smode black -tmode black -resize up].

Alternatively, you may use an HDR image. Load in the HDR image and convert it, but add the "-float" flag to create a floating point tiff which will preserve the high dynamic range information. It's like the above with the following addition:  
[txmake rmantex/rocks_intensity.tif -envlatl -smode black -tmode black -resize up -float]
For more info about converting your HDR images from the command line see: Note A - Working with HDR Imagery

2) Next you'll notice that by default an environment light is setup to cast reflections, specular effects. Diffuse effects are disabled by default. We must enable them:

Diffuse Effects -> Method -> "Occluded Environment"

The occluded environment will create nice soft shadows based on scene geometry while combining illumination from the environment map. 

3) Next we'll change the way that Specular Effects are generated. By default it is a simple blurry lookup of the map from the surface. We can get higher fidelty by sampling the environment:

Specular Effects -> Method -> "Sampled Environment"
 

Configure the environment map.
 

The map adjusted for light intensity --rocks_intensity.tif

5 - Image Based Lighting Controls

Now depending on what kind of material we want to create, we must adjust the parameters. 

The most important parameter the "Samples" parameter listed under the "Diffuse Effects" collection in the environment light setting. Low settings (64) will be faster but will be spotty. Higher settings (1024) will be much higher quality but take longer to render.  

Image based lighting
 

6 - Adjusting IBI

In the image on the right, we've added a matte shader to the floor by turning it's specularity to zero. For the dragon, we've created another shader which is shiny red.  

A matte shader attached to the ground
and a red shader attached to the dragon. 
      

A metal effect
  

Here's an example showing how glass objects can be created with image based lighting. Slim's Glass shading model can get illumination from scene lights or environment lights. 

Conclusion

Image based lighting can be used to create sophisticated lighting, without the use of any scene lights, soley through the use of environment maps. 

Slim's default shading models ready "out-of-box" for image based lighting. 

These effects can be used on their own or combined with traditional lighting techniques. 

Tips and tricks for working with IBI

Note A - Working with HDR Imagery

 
After the HDRI is converted you can load it into Slim, no need to convert it again because of Slim's new support for tiff textures.

Alternatively, you may convert an HDR image with Slim. Load in the HDR image and convert it like normal, but add the "-float" flag to create a floating point tiff which will preserve the high dynamic range information. It's like the above with the following addition:  
[txmake rmantex/rocks_intensity.tif -float]