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Old 17-03-2015, 09:35 AM
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This is similar to the debate about no need for calibration with Sony ccds.

Until you do the experiment and see that a flat actually adds noise to the image.

So this is relevant to noisy sensors more than anything. I would not have though Tony spent a lot of time with DSLRs. Perhaps his recent 60Da got him interested or he is trying to appeal to a wider audience than the CCD mob.

His DVDs on image processing are very good. I have watched them all. I don't particularly like his highly contrasted image processing but at least I know how he does it. He's like the original Pix Insight style image processor. He also several useful techniques that I use from time to time but some of it is getting a little dated now with advances in some software making the tricks redundant.

Greg.
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Old 17-03-2015, 10:34 AM
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Shiraz (Ray)
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Originally Posted by multiweb View Post
Hi Ray, no doubt dithering is a proven solution and a very powerful tool to remove noise and to some extend dust motes and other static patterns.
All the processes highlighted in the video aren't bad, but it is a bit rich to talk about noise reduction with non linear data. We might as well stack JPEG files and call it a day hey?
Hey, don't get me wrong, I am not advocating using the Hallas workflow, just saying that the main thrust of his presentation (and the title of this thread) is to do with DSLR noise reduction without using darks and flats - this part may be very sensible.

It would very sad if rejection of some parts of his presentation resulted in an overall impression that this means that the idea of using drizzle to get rid of noise (as an alternative to darks and flats) is equally questionable - it clearly is not. I wonder if drizzle stacking with hot pixel removal might possibly be even better than full calibration in the situation where darks, flats and lights are not fully temperature matched and where there is likely to be some form of low level manipulation of RAW data (eg a modern DSLR). I don't recall anyone ever posting any results either way.
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Old 17-03-2015, 11:25 AM
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Ray, why would you want/need to temperature match the flats?

Re: Noise, one can also do Gaussian pixel blurring to smooth out flat noise (but still retain sufficient definition of dust motes). I generally take 100 flats per filter/session to minimise noise, which is possible when using a light box.
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Old 17-03-2015, 11:27 AM
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multiweb (Marc)
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Hey, don't get me wrong, I am not advocating using the Hallas workflow
Not at all. I know you don't.
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Old 17-03-2015, 11:42 AM
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Ray, why would you want/need to temperature match the flats?

Re: Noise, one can also do Gaussian pixel blurring to smooth out flat noise (but still retain sufficient definition of dust motes). I generally take 100 flats per filter/session to minimise noise, which is possible when using a light box.
Hi Barry. The flats need to be dark subtracted (or at least bias subtracted). in either case, would expect that dark/bias level would vary with the temperature of the camera, so you could be subtracting a different bias from that inherent in the flat. Likely to be minor cf the mismatch of dark and lights, but still possible.

agree that if you do dither, hot pix rejection plus dither stacking gets rid of noise and then you can use smoothed flats to clean up any dust etc without adding more noise.
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