I am writing a Gaussian blur filter in graphics shader code. I want to make the blur parameterized by radius from the users perspective. The best method I can figure to do this is to pick a suitable stopping point for y, say .001, and solve for the variance to plug into the normal distribution function that will achieve that value of y.
Unfortunately I cannot for the life of me solve this equation for v...
$x = 10$ (blur radius)
$$.001 = \frac{1}{2 \pi v^2}e^{-\frac{x^2}{2v^2}}$$.