Reflections

Specular reflection is the perfect reflection of light from a surface. The law a reflection states that the direction of the incoming ray and the direction of the reflected ray produce the same angle about the surface normal. Perfect specular reflection produces a mirror like surface.

ReflectionsDuring the lighting calculation the reflected color is one component of the final pixel color. The reflectivity of the surface material determines how much the final surface color is derived from the surface color contribution and how much is contributed to reflected color. A mirror is fully reflective and has not color contribution from its surfaces.

Reflections

Reflections add more realism to computer generated images, but the viewer does not always pay close attention to what is visible in a reflection. This creates opportunity to use fake reflections. Traditional ray traced reflections can be time consuming, so finding shortcuts to simulate reflections can create more desirable render times. Environment maps are an efficient way of simulating a reflected environment.

Environment Maps

Using refection maps is an alternative method of simulating reflections. The reflected ray pulls a color value directly from an environment map instead of calculating the actual reflection. Instead of reflecting objects in the scene, the reflection is taken from image data stored in the environment map. A common type of environment map is a environment cube where each side of a cube is textured

ReflectionsRay traced reflections are the most accurate type of reflections, but they are render intensive. Additional rays are shot out into the environment to collect reflected color information.

ReflectionsRay traced reflections can produce perfect specular reflection. The incident vector is traced to the surface point and based upon the surface normal and incident vector direction a reflection ray is shot out into the environment and a color value is returned to produce the reflected color for that surface point.

Blurry ReflectionsIn order to simulate certain real world reflections, it is sometimes necessary to create blurry reflections for surfaces that are not perfectly specular like mirrors. Instead of the reflected ray bouncing in one direction, the reflected ray is broken down into multiple rays and bounced out in multiple directions returning multiple color values which are combined to produced the final color contribution from reflection for that surface point.

Blurry ReflectionsBlurry reflections take much longer to calculate that normal specular reflections. In some cases it makes sense to render a separate reflection pass and blur the reflected image before it is composited into the final frame. This can produce the look of blurry reflections without the long render times.

Refraction

Refraction occurs when the incoming ray strikes a transparent surface and travels through the surface. Just like reflected color, refracted color is one component of the final color. The transparency of the surface material determines how much of the final color is attributed to refracted color and the reflectivity of the surface material determines how much of the final surface color is attributed to reflected color.

Refraction

When a refracted ray enters a new material it changes direction. The degree of change is determined by Snell’s Law. Snell’s Law describes the relationship between the angle of incidence and the angle of refraction. The amount of refraction that occurs depends on the difference in Refractive Index of the two materials and is described by Snell's law: η1 sin θ1 = η2 sin θ2

The refractive index (η) equals the speed of light in vacuum divided by its speed in the material in question.

ExamplesAir = 1.0003Water = 1.33Glycerol = 1.47Immersion Oil = 1.515Crown Glass = 1.52Diamond = 2.42

Refraction