Let's improve grain


I like the proposed darktable noise. How does it compare to the current implementation at other “ISO” levels?

(Andrea Volpato) #42

To spot some differences one could look at the lightness histograms of the grain for 10%, 50% and 90% gray.

The darktable grain at 100% intensity has the following histograms.

The 10% and 90% histograms look a lot narrower. I wonder if it would be nice to tweak them so that they match your grain @Carmelo_DrRaw, which is more sophisticated.

It performs essentially in the same way since it is only a tweak of the weights and frequencies of the noise octaves.
Here are the power spectra trends.

For direct comparison here is the old implementation.

(Andrea Volpato) #43

@Carmelo_DrRaw, can I ask you a favor?
Could you apply the film grain of your implementation to this image:

I’m interested to see the full lightness profile of the grain.

(Carmelo Dr Raw) #44

Here is my result:

I can provide you results with other grain densities if needed…

(izara) #45

First of all, I think your work is very impressive, thank you for sharing it! Can I ask you a question? When you say:

“The light filtering trough the photographic film will be affected uniformly and we need to add the noise to the logarithm of the exposure.”

Why do you add the noise to the logarithm of exposure and not to the density of the film? I’m just wondering, maybe I don’t completely understand how the process works, because if the grain is in the film it should be added to the film, isn’t it?

And also, when you say uniformly you mean the noise follows a normal gaussian distribution?

Thank you in advanced!