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10-21-2010, 03:40 AM   #31
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QuoteOriginally posted by jolepp Quote
an ideal ADC would simply count the passing electrons as they are hoovered from each photosite by a voltage gradient and assuming it had a long enough counter any analog amplification would be only be a potential source of noise (?). The trouble is that an ADC can never be quite that accurate as electrons are elusive fellows due to the strangeness - from our point of view - of the quantum world they natively live in. Also, the practical ADC designs I know of are based on multiple analog voltage comparisons spread in in either in time (slow, simple, cheap) or space (fast, complex, expensive) so it seems they'd absolutely need the analog amplification for sample and hold at least.
I don't disagree.

An ideal image sensor sensel would detect the single moment where charge (an electron) is added and increment a counter right in the sensel (btw, the counter may not be possible to be embedded at every sensel; but to embedd a 64MB SDRAM memory bank right into the sensor chip creates huge opportunities like memory-limited rather than full well capacity-limited DR). By having to decide between 0 and 1, you can amplify by whatever factor to make the counting as noise free as possible. E.g., physicists sometimes use the avalanche effect in their experiments to make sure each and every electron is counted correctly. That may not be an option here (it's not impossible though) but you get the idea.


My only and initial point was that the CMOS sensor design goal is to make the measurement of the well charge as precise and noise-free as possible independently from the maximum number of electrons in the well. Therefore, to have a large or variable analog gain is not a design goal in itself and there is no reason to rant about high ISO being made in the digital domain. It would be if high ISO had large readout noise but this doesn't seem to be the case here.


Last edited by falconeye; 10-21-2010 at 03:46 AM.
10-21-2010, 06:54 AM   #32
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QuoteOriginally posted by falconeye Quote
Yes. Same if you would artificially add "grain" to an ISO 100 file for artistic reasons: the file size would grow. Holds true for JPG in particular.

It's the reason too why video at low light uses more of the 4GB limit than video at good light. Some people wonder why the K-7/5 stops recording video before the 4GB limit is reached. It does because it precomputes max. recording time with a lot of noise in mind.

The 30MB/Raw on the K-5 is kind of a maximum though, reached after lossless compression became impossible. I am not sure, but I think it is possible that the JPG quality depends on the ISO setting too (ie., it tries to compress more aggressively at higher ISO settings. Maybe, there's a difference between 3 and 4 star quality here).
Thanks!

I was wondering what was happening each time I used any NR whatsoever .... better be careful with this then!

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10-26-2010, 10:33 PM   #33
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Seems that GordonB is confirming the basic premises of my OP in the dpreview forum:
QuoteQuote:
2) All ISO's above 1600 are still achieved by digital multiplication.
3) Compulsory raw NR is still applied for all raw files of ISO 3200 and up (or maybe for above ISO 1600, I don't have samples of the 1/3 stop ISO's).
4) The compulsory raw NR applied above ISO 1600 is at about the same level as was applied for the k-x.
To put this compulsory raw NR into perspective, it applies an averaging/blurring of about a pixel diameter of about 1.33 pixels, which sounds like one would lose quite a bit of resolution other than this is a Bayer sensor so the maximum resolution that can be obtained is likely for an equivalent of about 1.25 pixel diameters, meaning that we are only losing about 7.5% in linear resolution to this compulsory raw NR that can't be turned off. Perhaps my only regret is that the NR would not start until ISO 6400 rather than 3200, but there is every change that the NR engine is cross hard-wired with the digital multiplication that produces the higher ISO sensitivities above 1600 and they can't be separated.
QuoteQuote:
But knowing this, one could shoot at max ISO 1600 (or just under the RAW NR threshold), and when higher effective ISOs are required use underexposure and push techniques in PP to achieve these.
QuoteQuote:
Yes, one could shoot at ISO 1600 and boost the EV compensation yourself in post processing, although the thumbnails and previews are going to be really dark and not too useful in confirming even a proper Auto Focus (AF) lock. Maybe there aren't any AF lock problems with the new AF system though
Regards, GordonBGood
Original post: Re: Stunning k-5...: Pentax SLR Talk Forum: Digital Photography Review
10-27-2010, 12:28 AM   #34
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QuoteOriginally posted by secateurs Quote
Seems that GordonB is confirming the basic premises of my OP in the dpreview forum:Original post: Re: Stunning k-5...: Pentax SLR Talk Forum: Digital Photography Review
I’m interested that you explain the various stages in the diagrams shown by Rawr

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