In-camera NR vs. separate darks

Started 1 month ago | Questions thread
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DavidWright2010 Veteran Member • Posts: 3,704
In-camera NR vs. separate darks

When I turn off 'long exposure noise reduction', and take some darks at the end of the session, the results are never as good as the in-camera noise reduction. Even considering that I could get twice as much light when I skip the in-camera NR (and therefore 1.4X better S/N, all other things being equal. it's still worse.

For quite a while I attributed this to 'operator error', and thought, with experience, it would be better.

But the noise is still worse using the classic workflow of separate darks.

So - another test.

Here are two exposures (each as part of a set). The camera is a Pentax K-1. The first is 15 seconds at ISO 1600 and f/10. With the in-camera NR, this took 30 sec. The RHS is the same exposure with in-camera NR turned off, and the 'master dark' subtracted (the master dark that DSS produced when I processed the full set of lights, darks, and flats)

I didn't just blindly subtract the dark from the light on the RHS - I adjusted the dark intensity to get the best improvement in S/N.

Then I used the app 'ImageJ' to get a plot of a line cut through these images:

LHS image:

RHS image:

I suppose I could draw ranges for the peak-to-peak (or RMS) noise and calculate a pair of S/N values, but by eyeball measurement, I'd say the LHS S/N is 30x the RHS value.

If the darks were as effective an in-camera NR, both images above should have the same S/N. (But the right produced in half the time.)

Here is a 100% crop from each image:

So has in-camera NR improved to the point that separate darks are no longer the best workflow?

Or is it still just me still not doing the classic worKflow correctly?


 DavidWright2010's gear list:DavidWright2010's gear list
Sigma DP1 Merrill Sigma DP2 Merrill Sigma DP3 Merrill Sigma SD1 Merrill Pentax K-1 +1 more
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Pentax K-1
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