Re: Megapixels and noise

"David J Taylor"
<david-taylor@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in
news:v8oKi.20516$c_1.4584@xxxxxxxxxxxxxxxxxxxxxxxxxx:

It would be interesting to change
it to Gaussian-distributed noise (i.e. normal white noise), and
perhaps allow an element of photon-limited noise.

Anyone have a nice function to simulate photon noise? I can do it in
Mathcad, but Mathcad only does poisson noise (and most other noises) by
creating a vector of poisson-distributed errors based on a single input
value, and to take an actual RAW file (or computer-generated image) with
low noise and simulate a much lower photon capture, I have to use Mathcad's
built-in function with each call for each pixel going through the process
of creating a vector (which is very slow), and then extracting one of its
elements to replace the original pixel.

I would like a function newval=poisson(val,scale) where scale is the
floating point number to scale the input (val) before creating poisson
error.

I thought about drizzling the original image onto a new, black image,
incrementing the pixels if they pass an "is the original greater than a
linear random number" test, after randomly selecting pixels, but I'm not
sure if that will give the correct results, and may take a while. However,
you may be able to watch the image grow, which would be interesting.

--

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John P Sheehy <JPS@xxxxxxx>
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