Re: Read noise: get it 30x down?
- From: Ilya Zakharevich <nospam-abuse@xxxxxxxxx>
- Date: Tue, 2 Oct 2007 08:51:17 +0000 (UTC)
[A complimentary Cc of this posting was NOT [per weedlist] sent to
Floyd L. Davidson
<floyd@xxxxxxxxxx>], who wrote in article <87y7elzzpz.fld@xxxxxxxxxx>:
Note that a 12-bit ADC has a maximum dynamic range of 72
dB, a 14-bit ADC has a maximum of 78 dB, and a 16-bit
ADC maxes out at 84 dB.
First, IMO using dB in the video context is very misleading (they have
an "extra" factor of 2).
Second, an ideal 12-bit ADC would give noise of about 1/2^14; so when
counting 6dB per 1/2 (instead of 3, as one should...), this is about
84dB. Your other numbers are WAY off.
Which is to say that the 12-bit ADC's typical work
right at their best SNR, while the SNR is greater than
the dynamic range for many of the ADC's with higher bits
per sample.
Correct numbers show that things are much worse than this. 12-bit
converters work approximately like 10-bit ideal converters.
When CCD's reach the point where a 16-bit ADC is needed
to deal with the CCD's dynamic range... we are going to
be simply *astounded* at the high ISO and low noise such
a combination produces! How about "quality" low noise
images at ISO 52,000, and absolutely useful images at
208,000?
You are forgetting about very low QE of the current (well, 2-years
old) generation of sensors (about 0.1). So with non-RGB-Bayer
sensors, the numbers could be quite significant.
Decreasing the read noise well below 3e has, IMO, only one use: you
can bin the pixels by postprocessing; so you can trade resolution vs
noise very late in the pipeline (e.g., before printing), do it
adaptively, and apply intelligent algorithms for choosing the
tradeoffs.
Increasing QE gives much more direct advantage. And anyway, I do not
think that the numbers you cite are attainable without signficant
decrease in resolution.
Hope this helps,
Ilya
.
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