Denoise only dark areas? Luma key?

[Lyris]

Hey forum,
I have a source here that has a lot of noise in dark areas that needs reduced.

FFT3Dgpu(sigma=6) effectively kills this, but of course kills details in other areas to an unacceptable extent.

How do I merge the FFT3D'd filtered version and the original, using the original for most of the luminance range but switching back to the noise filtered version for a range of levels, say 0-10?

I can't post a sample on this occasion, sadly... but hopefully it's a clear enough description.

[feisty2]

a=last
g_mask=mt_lut("x 128 >= 255 x 16 <= 0 x 16 - 255 * 112 / ? ?").mt_invert()
denoise=FFT3Dgpu(sigma=6)
mt_merge(a,denoise,g_mask)

[Lyris]

Thank you my good sir :) And the "Useful AVIsynth scripts" folder grows once more!

[lisztfr9]

The idea has the drawback to reduce the amount of details in hairs, often dark.

L

[Forensic]

I have had very good success with TemporalDegrain(degrain=3,ov=4,blksize=16,HQ=2)
These settings preserve details, especially at the lower luma levels.