Signal to noise ration (SNR) in relation to senor size and pixel density

Discussion in 'Digital Photography' started by john, Dec 6, 2003.

  1. john

    john Guest

    There's been many posting about this subject, but i don't quite understand
    why a bigger sensor can have a better SNR, while increasing the pixel
    density on a fixed size may result in more noise.

    is there any websites that explains this?

    thanx in advance.
     
    john, Dec 6, 2003
    #1
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  2. Re: Signal to noise ration (SNR) in relation to senor size and pixeldensity

    john wrote:
    > There's been many posting about this subject, but i don't quite understand
    > why a bigger sensor can have a better SNR, while increasing the pixel
    > density on a fixed size may result in more noise.
    >
    > is there any websites that explains this?


    I don't know of a website but I know the answer. A bigger sensor tends
    to also have larger light gathering sites. The fact that they can
    gather more light means they don't have as much "room" for noise.
    Cramming more, smaller pixels into a sensor means those sensors have
    less light gathering capability.

    So, based on that a 5mp CCD that is the same size as a 4mp CCD will have
    more noise because the individual sensors have less light gathering
    capacity.

    Obviously the amount of noise will depend on the quality of the sensor
    and since technology is improving all the time this is subject to change.
     
    Andrew McDonald, Dec 6, 2003
    #2
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  3. john

    Don Stauffer Guest

    Re: Signal to noise ration (SNR) in relation to senor size and pixeldensity

    There can be many contributions to noise, but there are indeed two
    sources that depend on pixel size. The first is photon noise. The
    smaller a pixel for the same scene brightness and exposure, the fewer
    photons strike each pixel. Since we cannot have fractional photons,
    there is a stairstep function here and that stairstep response is a form
    of noise.

    Closely related is electron shot noise. The smaller the pixel, the
    smaller the capacitance well the photon-generated electrons are stored
    in before readout. Since we cannot have fractional electrons, the ratio
    of one electron to the maximum electron capacity of the storage well
    (capacitor) is essentially the best possible dynamic range. Low dynamic
    range and signal-to-noise are essentially the same thing.

    The first problem is particularly bad in dim light, and is why digital
    cameras seem noisier than film in dim light.

    john wrote:
    >
    > There's been many posting about this subject, but i don't quite understand
    > why a bigger sensor can have a better SNR, while increasing the pixel
    > density on a fixed size may result in more noise.
    >
    > is there any websites that explains this?
    >
    > thanx in advance.


    --
    Don Stauffer in Minnesota

    webpage- http://www.usfamily.net/web/stauffer
     
    Don Stauffer, Dec 6, 2003
    #3
  4. Re: Signal to noise ration (SNR) in relation to senor size and pixel density

    "Don Stauffer" <> wrote in message
    news:...
    > There can be many contributions to noise, but there are indeed two
    > sources that depend on pixel size. The first is photon noise. The
    > smaller a pixel for the same scene brightness and exposure, the fewer
    > photons strike each pixel. Since we cannot have fractional photons,
    > there is a stairstep function here and that stairstep response is a form
    > of noise.
    >
    > Closely related is electron shot noise. The smaller the pixel, the
    > smaller the capacitance well the photon-generated electrons are stored
    > in before readout. Since we cannot have fractional electrons, the ratio
    > of one electron to the maximum electron capacity of the storage well
    > (capacitor) is essentially the best possible dynamic range. Low dynamic
    > range and signal-to-noise are essentially the same thing.
    >
    > The first problem is particularly bad in dim light, and is why digital
    > cameras seem noisier than film in dim light.
    >


    And here I was thinking I could have an intelligent conversation with anyone
    about anything.

    Juan
     
    Juan R. Pollo, Dec 6, 2003
    #4
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