Canon A300: What resolution when zoom in 5x? Calculation?

Discussion in 'Digital Photography' started by lbbss, Jun 10, 2004.

  1. lbbss

    lbbss Guest

    Can someone explain this to me? when you zoom in at 5.1x with a 3.1 mega
    pixel camera, what resolution do you get?
    I am thinking of buying canon A300, and wanted to know what resolution I
    would get when using the digital zoom. Calculation 3.1 divided by 5.1
    = 0.63 mega pixels? Is that correct calculation?
     
    lbbss, Jun 10, 2004
    #1
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  2. lbbss

    John Briggs Guest

    "lbbss" <> wrote in message
    news:...
    > Can someone explain this to me? when you zoom in at 5.1x with a 3.1 mega
    > pixel camera, what resolution do you get?
    > I am thinking of buying canon A300, and wanted to know what resolution I
    > would get when using the digital zoom. Calculation 3.1 divided by

    5.1
    > = 0.63 mega pixels? Is that correct calculation?
    >
    >


    I don't think so. The 5.1x is in both width and height so the area
    magnification is 5.1 x 5.1 = 26.01. So you would get 3.1/26.01 = 0.119MP.
    Note also that the camera would still save the image at the current setting
    for resolution by interpolating pixels. So at highest resolution you would
    still get a 3.1MP image - it just wouldn't look very good!

    Some Sony cameras have a so-called "smart zoom" which you can only use at
    lower resolution settings. This effectively just crops the centre portion of
    a full resolution image and shouldn't need to interpolate pixels.

    I don't know if the A300 has an optical zoom but you'd be much better off
    with optical rather than digital zoom.

    John
     
    John Briggs, Jun 10, 2004
    #2
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  3. "lbbss" <> writes:
    >Can someone explain this to me? when you zoom in at 5.1x with a 3.1 mega
    >pixel camera, what resolution do you get?
    >I am thinking of buying canon A300, and wanted to know what resolution I
    >would get when using the digital zoom. Calculation 3.1 divided by 5.1
    >= 0.63 mega pixels? Is that correct calculation?


    No.

    With most cameras, you first have to separate the optical and digital
    zoom factors. Optical zoom gives real resolution increase, digital zoom
    does not. I think the A300 does not have any optical zoom, so this
    isn't a factor.

    Now, a digital zoom factor of 5 means an enlargement of 5 times in both
    width and height, so an area that was originally 1/25 of the image is
    enlarged to fill the whole image area. In this case, with 5.1X digital
    zoom, the number of sensor pixels contributing to the output is

    3.1 / (5.1*5.1) = 0.12 megapixels, or 120 kpixels

    or about 400x300 pixels.

    Thus, any final image size larger than 400x300 is likely to look
    unsharp.

    Dave
     
    Dave Martindale, Jun 11, 2004
    #3
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