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Noise levels as a function of pixel size



 
 
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  #1  
Old December 13th 05, 04:53 PM posted to rec.photo.digital,rec.photo.digital.slr-systems
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Default Noise levels as a function of pixel size

Is there some formula or scientific basis to estimate noise levels as a
function of pixel size? At the moment I'm assuming that noise levels
decrease with the square root of the size increase, i.e. doubling the
pixel area should lower noise levels by the square root of 2. Is this
correct? I'm only referring to "pixel" noise, i.e. not read noise, A/D
conversion noise and other external noise sources.
--

Alfred Molon
------------------------------
Olympus 50X0, 7070, 8080, E300, E500 forum at
http://groups.yahoo.com/group/MyOlympus/
Olympus E500 resource - http://myolympus.org/E500/
  #2  
Old December 13th 05, 05:09 PM posted to rec.photo.digital,rec.photo.digital.slr-systems
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Default Noise levels as a function of pixel size

Alfred Molon wrote:
Is there some formula or scientific basis to estimate noise levels as
a function of pixel size? At the moment I'm assuming that noise levels
decrease with the square root of the size increase, i.e. doubling the
pixel area should lower noise levels by the square root of 2. Is this
correct? I'm only referring to "pixel" noise, i.e. not read noise, A/D
conversion noise and other external noise sources.


The photon-limited noise is proportional to the square root of the number
of photons collected. So, if everything else is equal, a pixel which is
double the linear size will connect four times the number of photons, and
the noise will be twice as much. Therefore the signal to noise ratio will
be doubled.

Doubling the area will increase the signal-to-noise ratio by a factor of
square root (2), with the signal being doubled and the noise being root 2
higher.

David


  #3  
Old December 13th 05, 05:56 PM posted to rec.photo.digital,rec.photo.digital.slr-systems
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Default Noise levels as a function of pixel size

On Tue, 13 Dec 2005 16:53:06 +0100, Alfred Molon wrote:
Is there some formula or scientific basis to estimate noise levels as a
function of pixel size? At the moment I'm assuming that noise levels
decrease with the square root of the size increase, i.e. doubling the
pixel area should lower noise levels by the square root of 2. Is this
correct? I'm only referring to "pixel" noise, i.e. not read noise, A/D
conversion noise and other external noise sources.


Photon counting is a Poisson statistics problem, so the noise goes like
the square root of the signal. The signal/noise ratio thus goes like
1/sqrt(signal). Doubling the linear size of a pixel increases the area
(and hence the signal) by a factor of four. The noise only doubles, so
s/n doubles.

More generally, the s/n ratio scales with the linear size of the pixel.

-dms
  #4  
Old December 15th 05, 08:37 PM posted to rec.photo.digital,rec.photo.digital.slr-systems
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Default Noise levels as a function of pixel size

In article ,
Alfred Molon wrote:

Is there some formula or scientific basis to estimate noise levels as a
function of pixel size?


No. Try a Kodak 14n and a Canon 5D both at iso 1600, and you'll see.

Lourens
  #5  
Old December 15th 05, 08:48 PM posted to rec.photo.digital,rec.photo.digital.slr-systems
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Default Noise levels as a function of pixel size


Lourens Smak wrote:
In article ,
Alfred Molon wrote:

Is there some formula or scientific basis to estimate noise levels as a
function of pixel size?


No. Try a Kodak 14n and a Canon 5D both at iso 1600, and you'll see.

Lourens


There are limits to noise performance base on pixel size. Not every
camera comes close to these limits, but no camera passes them.

Scott

  #6  
Old December 15th 05, 09:36 PM posted to rec.photo.digital,rec.photo.digital.slr-systems
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Default Noise levels as a function of pixel size

I don't see why this would be any different than low noise amplifier
design, so double the area and the SNR improves by 3db (linear square
root of two).

I don't know if cameras do this, but you could sample the sensor with
the shutter closed, then sample with the shutter opened. A certain
amount of noise will be cancelled. [Double correlated sampling.]

Alfred Molon wrote:
Is there some formula or scientific basis to estimate noise levels as a
function of pixel size? At the moment I'm assuming that noise levels
decrease with the square root of the size increase, i.e. doubling the
pixel area should lower noise levels by the square root of 2. Is this
correct? I'm only referring to "pixel" noise, i.e. not read noise, A/D
conversion noise and other external noise sources.
--

Alfred Molon
------------------------------
Olympus 50X0, 7070, 8080, E300, E500 forum at
http://groups.yahoo.com/group/MyOlympus/
Olympus E500 resource - http://myolympus.org/E500/


  #7  
Old December 15th 05, 09:51 PM posted to rec.photo.digital,rec.photo.digital.slr-systems
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Default Noise levels as a function of pixel size


"Lourens Smak" wrote in message
...
In article ,
Alfred Molon wrote:

Is there some formula or scientific basis to estimate noise levels as a
function of pixel size?


No. Try a Kodak 14n and a Canon 5D both at iso 1600, and you'll see.

Lourens




Yes, there is scientific basis to estimate noise levels as a function of
pixel size.

The intrinsic noise from the CCD or CMOS pixel is mainly a function of
thermal energy, and independent of pixel size. The signal is a result of
light hitting the pixel surface, which is a function of pixel size because a
larger pixel collects more light. Therefore a larger pixel will have a
higher signal to noise level. So if you get the same signal output, a larger
pixel will have less noise than a smaller pixel.


Wannabe
=======

  #8  
Old December 16th 05, 12:04 AM posted to rec.photo.digital,rec.photo.digital.slr-systems
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Default Noise levels as a function of pixel size

Lourens Smak wrote:

In article ,
Alfred Molon wrote:

Is there some formula or scientific basis to estimate noise levels as a
function of pixel size?


No. Try a Kodak 14n and a Canon 5D both at iso 1600, and you'll see.



And the 'full frame' 6 MP Contax N Digital has noise levels that are
even worse than the Kodak!

Far worse, in fact, even at low ISO.

;-)

  #9  
Old December 16th 05, 01:02 AM posted to rec.photo.digital,rec.photo.digital.slr-systems
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Default Noise levels as a function of pixel size

Alfred Molon wrote:
Is there some formula or scientific basis to estimate noise levels as a
function of pixel size? At the moment I'm assuming that noise levels
decrease with the square root of the size increase, i.e. doubling the
pixel area should lower noise levels by the square root of 2. Is this
correct? I'm only referring to "pixel" noise, i.e. not read noise, A/D
conversion noise and other external noise sources.


See "http://clarkvision.com/imagedetail/does.pixel.size.matter/"
 




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