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DGS Exploited

By Florian Wild
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Date Added: 9th December 2009
Software used:
Maya, mental ray

The dgs (left sphere) is obviously much darker - just a matter of settings you'd say. So let's tweak them a bit - let's increase the dgs' diffuse to total white:

500_tid_image_03.jpg
Better, but still very dissatisfying - and the 'Color' attribute of our phong is still darker (0.5 value!) than the dgs' diffuse color. What is the cause of this discrepancy? Having a look at the dgs shader sources, which are freely availabe we see the reason for this. A line of comment says (and it's also applied later on in the code):

[code]* m->diffuse is reflectance rho (0 <= rho <= 1). BRDF f_r = rho/pi.[/code]

This means, the radiance (rho), is being divided by pi (approx. 3.1415etc...). Uhm..

[interlude]
What does radiance actually mean? Here's some useful links describing the term:
http://www.dotcsw.com/poy2001.txt
http://en.wikipedia.org/wiki/Radiance
http://en.wikipedia.org/wiki/Luminance

So radiance is used to indicate how much power will be received by an optical system looking at the surface from a certain angle. The division by pi will be explained later on.
[/interlude]

How could we achieve what the dgs is internally doing, with our Maya shader? You guessed it, let's use the 'Diffuse' attribute of our Lambert material, which acts as a simple multiplier to the 'Color' value. Since we cant literally divide, we need to multiply by the fraction: 1/pi (approx. 0.318). Let's do it:

500_tid_image_04.jpg

Oops, what went wrong? Sure, we set our dgs' diffuse color to white before, let's do so with our phong.
Set the phong 'Color' to total white:

500_tid_image_05.jpg




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