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11-18-2008, 01:50 PM   #1
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Higher pixel count produces less noise...?

Well, this thread I read topples the idea I have about sensors.

http://www.dxomark.com/index.php/eng/Insights/More-pixels-offsets-noise!

I am a little puzzled by the science behind the testing.

Maybe someone could share the wisdom around!

11-18-2008, 01:59 PM   #2
Damn Brit
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Let me know if you get it figured out James. It's way over my head so I can't let stuff like that interfere with my photography.
11-18-2008, 02:04 PM   #3
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QuoteOriginally posted by Damn Brit Quote
Let me know if you get it figured out James. It's way over my head so I can't let stuff like that interfere with my photography.
Gary, I often left the discussion to the know-it-all

However, I do take away a few basic principles just for the interest of it. However, the statement really changes my way of thinking about measurebation to a degree (After all, I often pixel peep and read about technological data and dismissing them all)

This one puzzles me!
11-18-2008, 02:04 PM   #4
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Then this is the comparison between k20d and k10d sensor

Not much difference at all!!

http://www.dxomark.com/index.php/eng/Image-Quality-Database/Pentax

11-18-2008, 02:08 PM   #5
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i'm having a hard time getting it as well

but i think it has alot to do with the camera's brain.

since each pixel only records a single colour, there is alot of extrapolation that goes during writing time

perhaps noise is also in that equation.

extrapolating 4 weaker signals from 4 pixels ends up being better than the 1 single signal.

again thats just my laymens understanding of it.



(not to mention the fact that the pixels themselves are PHYSICALY more advanced with each new sensor development, consume less electricy, heat up less, cool faster and have less overflow)
11-18-2008, 02:42 PM   #6
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Well I'm not sure what your understanding about sensors are, but if it's similar to mine I don't think this article would topple it

I'm guessing what you've generally come to understand is this: the smaller the size of the pixel on the sensor, the more noise that pixel will have.

This article isn't disputing this, it is arguing on the method to compare noise between sensors that have different resolution/sensor size.

Imagine this hypothetical two camera scenario: you have a 1-megapixel camera and a 4-megapixel camera with identical sensor sizes (APS-C for example). Because of the pixel density (each pixel of the 4-meg sensor is 1/4 the size of the pixel on the 1-meg sensor) you'd expect the 4-meg sensor to have 4x the noise. All this article is saying that it's not fair to say this 4-meg camera is noiser than the 1-meg camera, because you can reduce the resolution of the 4-meg image in PP 4x to reduce the noise by 4x, which gives you the equivalent of the 1-meg camera's. So in this case the noise is essentially the same.

But, lets say because of technological advances the 4-meg pixel camera manages to only be 3x noisier per pixel, you would actually have a overall less noisy sensor in the 4-meg camera compared the the 1-meg camera. Per pixel the 4-meg camera would look noisier, but you'd still get a less noisy output if printing to the same size.
11-18-2008, 03:43 PM   #7
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QuoteOriginally posted by wcleong Quote
Well I'm not sure what your understanding about sensors are, but if it's similar to mine I don't think this article would topple it

I'm guessing what you've generally come to understand is this: the smaller the size of the pixel on the sensor, the more noise that pixel will have.

This article isn't disputing this, it is arguing on the method to compare noise between sensors that have different resolution/sensor size.

Imagine this hypothetical two camera scenario: you have a 1-megapixel camera and a 4-megapixel camera with identical sensor sizes (APS-C for example). Because of the pixel density (each pixel of the 4-meg sensor is 1/4 the size of the pixel on the 1-meg sensor) you'd expect the 4-meg sensor to have 4x the noise. All this article is saying that it's not fair to say this 4-meg camera is noiser than the 1-meg camera, because you can reduce the resolution of the 4-meg image in PP 4x to reduce the noise by 4x, which gives you the equivalent of the 1-meg camera's. So in this case the noise is essentially the same.

But, lets say because of technological advances the 4-meg pixel camera manages to only be 3x noisier per pixel, you would actually have a overall less noisy sensor in the 4-meg camera compared the the 1-meg camera. Per pixel the 4-meg camera would look noisier, but you'd still get a less noisy output if printing to the same size.
That seems to be essentially it. I might argue this point though:
Now assume that the same exposure times and identical ISO settings are used with a low-resolution camera and with a high-resolution camera having four times as many pixels. Since each high-resolution pixel is intrinsically less sensitive, a higher gain (either analog or digital) is applied to the signal, yielding more noise.
From what I read read noise is independent of pixel size and more dependent on the quality of the circuitry.... I can't see the above as correct (though it may be).
Even a difference in microlenses would increase the "efficiency" of a small sensor...
http://www.qsimaging.com/ccd_noise.html
More noise:
http://forums.dpreview.com/forums/read.asp?forum=1018&message=28611331&q=pix...AND+noise&qf=m
http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html#pixelsize
Bottom line: Among the important measures of image quality are signal-to-noise ratio of the capture process, and resolution. It was shown that for fixed sensor format, the light collection efficiency per unit area is essentially independent of pixel size, over a huge range of pixel sizes from 2 microns to over 8 microns, and is therefore independent of the number of megapixels. Noise performance per unit area was seen to be only weakly dependent on pixel size. The S/N ratio per unit area is much the same over a wide range of pixel sizes. There is an advantage to big pixels in low light (high ISO) applications, where read noise is an important detractor from image quality, and big pixels currently have lower read noise than aggregations of small pixels of equal area. For low ISO applications, the situation is reversed in current implementations -- if anything, smaller pixels perform somewhat better in terms of S/N ratio (while offering more resolution). A further exploration of these issues can be found on the supplemental page. Rather than having strong dependence on the pixel size, the noise performance instead depends quite strongly on sensor size -- bigger sensors yield higher quality images, by capturing more signal (photons).

The other main measure of image quality is the resolution in line pairs/picture height; it is by definition independent of the sensor size, and depends only on the megapixel count. The more megapixels, the more resolution, up to the limits imposed by the system's optics.

Last edited by jeffkrol; 11-18-2008 at 04:13 PM.
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