I'm a little confused about the gaussian filter function which can be found on several sources.

What's confusing to me is that I've found at least 3 different equations for the same thing...

I've marked the differences in red color.

Wikipedia lists it as: (http://en.wikipedia.org/wiki/Gaussian_filter)

g(x) = (1 / (sqrt(2 * PI) * rho)) * exp(-(x*x) / (2 * (rho * rho)))

While the one found in Real-Time-Rendering, Third Edition defines it as:

g(x) = (1 / (sqrt(2 * PI) * rho * rho)) * exp(-(x*x) / (2 * (rho * rho)))

And finally the code that I've got from one of MJP's samples:

g(x) = (1 / (sqrt(2 * PI * rho * rho))) * exp(-(x*x) / (2 * (rho * rho)))

What am I missing here ?

Not sure what you mean by "Assuming that you meant to divide by rho instead of multiplying by rho at all places". What scaling are you talking about ?

RTR defines it as: http://d.pr/i/3Dsg

Where is this squared rho coming from ?

Hmm, I'd imagine the RTR is a typo because typically you don't want to scale and you want to be normalized to 1 when you integrate over the domain -\inf to \inf. That's what the term out in the front is for. I don't have the book on me at the moment to see in context what they are talking about.

-= Dave

Ah yes sorry I keep confusing these symbols names (maybe I should just call it the standard deviation ) and yes it seems I've made some mistakes in the parentheses (fixed it now) but that scaling factor is basically what I'm confused about the reason why it's in there.