Project files: glossyreflections.zip

Since reflective materials are generally not perfect mirrors, the reflected image tends to look more or less blurred. Materials with aligned micro structures, such as brushed metals, may also look anisotropically blurred, making the reflections stretch out in one direction.

The scene contains a metallic cylinder on a marble table, in order to introduce the various features of glossy reflections. 

Enabling Glossy Reflections

Rendering the image as it is in the scene gives the following result:

The reflection of the table looks unrealistically sharp. To change this, select the metal material on the cylinder and open the Turtle settings. Since this is a reflective material, it has a Glossy Reflections section:

Check the Glossy Reflections box and render again.

The reflection on the cylinder is now much blurrier but also a bit noisy as well.

This cylinder looks too blurry, let's increase the Sharpness value on s_cylinder node to 500.

The cylinder is now somewhat less blurry, but it's still noisy in some parts of the reflection.

Decreasing the noise

Insufficient sampling of glossy reflections shows up as noise in the image. Extremly unsharp reflections in particular will be noisy. There are two ways of decreasing this noise; either increase the global Super Sampling settings or increase the number of Reflection Rays in the material settings.

Let's increase the Maximun Rays on the s_cylinder node to 25.

Now most of the noise is gone. Increasing the number of rays further will decrease the noise even more.

Combining Glossy Reflections and HDRI Environments

We can add a HDRI environment using the Image Based Lightning feature of Turtle. We will use the kitchen hdri-file from Paul Devebecs homepage. The Image Based Lightning we will use are:

Rendering the image gives the following result, the reflected environment is also glossy:

Anisotropic Glossy Reflections

Now assign the shader s_cylinderAnisotropic to the p_cylinder object. Enable Anisotropic box of the glossy material settings to give the cylinder a brushed look. In addition to this, the Sharpness and Spread parameters has to be tuned to give a good result.

Understanding Sharpness and Spread

The tangents of the surface defines the direction in which the surface will look brushed when using anisotropic glossy reflections. Having a large value for SpreadX will spread out the reflection along the tangents and a large value of SpreadY will spread it out perpendicular to the tangents. If they are the same the material won't look anisotropic at all.

To emphasize the anisotropic aspects, change the value of spreadY to 1.

A rendering of the scene gives the following result:

Rotating the Anisotropic Direction

Finally let's rotate the direction of anisotropy. This is done by altering the angle parameter of the glossy material settings. To match the Maya anisotropic shader interface a rotation of 180 degrees means 90 degrees in the Turtle glossy settings.

Finding good parameters for anisotropic settings may be difficult. This image shows a few settings:

From left to right:

• No glossy reflections
• Sharpness 80, Maximum rays 25, non Anisotropic
• Sharpness 400, Maximum rays 25, Anisotropic, SpreadX 80, SpreadY 1
• Sharpness 400, Maximum rays 25, Anisotropic, SpreadX 1, SpreadY 80

Summary

Glossy Reflections may improve the look of all reflective surfaces. There is a lot of parameters to change that helps you customizing the result and make the reflections look exactly the way you want them to.

The Ashikimin Shader

The Ashikimin surface shader is especially suited for anisotropic glossy metallic objects. The main differences between the Ashikimin shader and the standard Maya anisotropic shader is that the specular highlights and glossy reflection always match up in the Ashikimin shader and that you can attenuate the reflections.

Attenuated Reflections

The Ashikimin shader can attenuate the glossy reflections after a distance. A distance less than the start attenuation will be treated as usual. Everything with a greater distance than the end attenuation will be sampled in an environment map. In the area inbetween Turtle will crossfade between the proper reflection and the environment map. You can connect a standard environment map to the shader, use the camera environment or connect a IBL reflection map. If you use the shader reflected color node, you must connect an env. shader. Only altering the color will not affect it. Consider the image below.  

The first is the standard glossy shader with no attenuation. The other two show to different types of attenuation. The attenuated ones have a grey environment map connect to them. The attenuated ones are much less noisy than the standard one. You can see this from the sampling image below (white is 32 samples/pixel, black is 1 sample/pixel).

This is of course a very simple example to demonstrate the functionality. Using the Ashikimin shader with a scene specific environment map generated with Turtles environment cameras can yield very good looking results in much less time than a "proper" glossy reflections.

Caveats

Inconsistent UV mapping will produce strange results.

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