Re: Pixel size of individual Pixel

Discussion in 'Digital Photography' started by Robert E. Williams, Sep 14, 2003.

  1. Pdelpriore wrote:

    > Anyone know the dimension of one pixel in the CCD array of theNikon Coolpix
    > 885?
    >
    > Paul


    Well, the sensor size is 7.18 X 5.32 mm. (Usually referred to as 1/1.8")
    That is about 38.2 million square microns
    The sensor has 3.34 million sensor cells (3.14 million actually form the image)

    Sooo, each sensor cell occupies 11.44 square microns, or 3.38 x 3.38 microns.
    Of course, there is a little unused space between cells so each active site is
    somewhat smaller than 3.38 microns on a side.
    But for purposes of comparison I always just use the gross size.
    The size of an individual sensor cell is very important, because the larger it
    is, the greater is the signal/noise ratio and the better is the color purity of
    the signal.
    5 MP images on a 1/1.8" sensor, just about push the quality limits at the
    present time.
    Many folks feel that 4MP images from a 1/1.8" sensor are better than 5 MP
    images from the same size sensor.
    Slightly less resolution but better color rendition and less noisy.
    Seems like everything in life is a tradeoff.
    Bob Williams
    Robert E. Williams, Sep 14, 2003
    #1
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  2. >Robert E. Williams on Sunday 14 September 2003 00:44 wrote:

    >> Sooo, each sensor cell occupies 11.44 square microns, or 3.38 x
    >> 3.38 microns. Of course, there is a little unused space between
    >> cells so each active site is somewhat smaller than 3.38 microns on a
    >> side. But for purposes of comparison I always just use the gross
    >> size.


    Stefan Patric <> writes:
    >IIRC, the average size
    >of the actual light sensitive diodes in 1/1.8" CCDs is around 3 to 4
    >microns, not 11.


    He said they were 3.38 microns on a side, which agrees with what you
    remember. The "11" number is the *area* in square microns, not the
    pixel pitch. 3.38^2 = 11.4.

    Dave
    Dave Martindale, Sep 16, 2003
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  3. Robert E. Williams

    Don Stauffer Guest

    We need to differentiate here between the size of a pixel and a
    detector. A pixel is an element of the grid that makes up the image.
    That is, the dimension of a pixel is the center-to-center spacing of the
    array.

    The actual photosensor element can never be larger than a pixel, but may
    be substantially smaller. A smaller detector (low fill factor, as the
    terminology goes) makes almost NO difference in resolution. It can
    affect sensitivity.

    Actually, lower fill factor does do a slight edge sharpening, or at
    least tends to peak the MTF at higher spatial frequencies, but this is a
    relatively minor effect.

    Some high fill factor chips can have a slight crosstalk problem, but
    again the effect is generally minor.

    In summary, the pitch of the array, i.e, the pixel size, is what
    determines resolution. Other than the sensitivity effect, the fill
    factor, or percentage of the pixel area actually sensitive to light, is
    not that much of a concern.

    One qualification to the detector never being larger than a pixel is
    that in some arrays the actual photosenstive region is NOT
    differentiated into pixels, but is continuous. But the
    collecting/storing electrodes still define the effective detector size
    for the pixel.

    --
    Don Stauffer in Minnesota

    webpage- http://www.usfamily.net/web/stauffer
    Don Stauffer, Sep 16, 2003
    #3
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