Olympus-OM
[Top] [All Lists]

Re: [OM] Digital Noise

Subject: Re: [OM] Digital Noise
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Tue, 22 Sep 2015 10:16:07 -0400
That's because you didn't read the footnotes to part 2

--------------------------------------------------------------
Footnotes

*1 The most salient noise sources upstream of ISO amplification include reset noise, pixel amplifier noise, and dark current shot noise for longer exposures (which we won't dive into). Reset noise originates from variations in the voltages each pixel is reset to after a charge is read (ideally, they'd all be reset to the exact, same voltage). These variations - that show up as changes in intensity across neighboring pixels - can largely be mitigated by a process called correlated double sampling (CDS), which samples and subtracts the reset voltage at any pixel from the total voltage due to exposure. It can almost be thought of as a dark frame subtraction, and is very effective, lowering pixel-to-pixel variations, as well as pixel-level amplifier noise, to the level of single electrons in modern sensors. However, CDS isn't completely effective, and so a non-zero noise component still remains. For reasonable exposure lengths, any remaining reset and pixel amplifier noise post-CDS are probably the largest sources of upstream read noise. [Jump back to text]

*2 Downstream read noise includes all sources from and after, or 'downstream of,' ISO amplification. This includes noise from the programmable gain amplifier (set by your ISO setting), noise from the analog to digital conversion process, as well as any noise introduced in the pathways between all these electronic components in your camera. [Jump back to text]

*3 How much of this light a camera is able to make use of depends on its sensor efficiency, which is beyond the scope of this article. We mention it here, though, because sensors with higher efficiencies will record more of the available light during any given exposure: leading to less shot noise and a slightly cleaner result in our exposure latitude test. [Jump back to text]

*4 There are other sources of noise that are beyond the scope of this article. Thermal noise builds up with long exposures, amplifier glow can lead to 'hot spots' at the edges of your image, pixel-response non-uniformity can lead to noise even in brighter areas of your image, and quantization error further limits signal-to-noise ratio in shadows. [Jump back to text]
-------------------------------------------------------------------------

Chuck Norcutt



On 9/22/2015 8:47 AM, Wayne Harridge wrote:
Thanks (I think) for that reference Moose.

Unfortunately I don't think it addresses increased noise from long
exposures, ok the relative shot noise increases when the amount of light
hitting the sensor is low and you tend to use longer exposures when the
light level is low, but this is also the time when you also might opt for
high ISO.  No mention of increased noise at long exposures due to heating of
the sensor.
--
_________________________________________________________________
Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
Archives: http://lists.thomasclausen.net/mailman/private/olympus/
Themed Olympus Photo Exhibition: http://www.tope.nl/

<Prev in Thread] Current Thread [Next in Thread>
Sponsored by Tako
Impressum | Datenschutz