Common Refraction Questions

By Ray Dream Technical Support. April 1995.
Below are some common questions regarding Refraction settings in Ray Dream Designer 3 and how they are calculated.

Q: How does the RDD refraction value of 0-100 relate (if at all) to real world refraction indexes (Hard to think of considering the limited range of indexes. For example, glass has a refraction index between 1 and 1.5, a diamond about 4)
A: The Index of refraction = 100 / (100 - Slider value) This equation is an approximation, but should be close enough.
Q: When having 'lighting through transparent objects' selected in the rendering options, does Designer take into account the thickness and curvature of an object when calculating refraction?
A: Refraction is calculated at surface normals. Curvature is taken into account. Since refraction is calculated on every surface, if you place a refractive sphere in front of a pattern, the pattern will be refracted twice before it hits the camera. Once when it enters the sphere and again when it exits the sphere.
Q: If using a grayscale texture map to specify varying levels of refraction, how do 255 possible levels of gray correlate to values from 0-100...i.e. how would the acceptable glass refraaction value of 3 be represented in grayscale?
A: The correlation is linear (i.e. a gray value of 127 would be about 50. The conversion factor is 2.55. The index of refraction of glass would be 1.5 which would be a numerical value of about 39 which would be a gray value of about 100 (39 * 2.55).
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RDD Refraction / David Ramirez / dram@netcom.com / 11 September 1995