Image size/quality

Discussion in 'Photography' started by J, Jan 8, 2012.

  1. J

    J Guest

    Something I always wondered....'anyone know? :)

    Y'know when you select 'image size' on a digital camera and you can select
    1MP, 2MP, 5MP, 10MP and so on.
    Knowing that there is only one sensor in the camera (say 10MP), how exactly
    does the camera achieve this 'downsizing' to give a smaller pic, and how
    does it affect the image quality?

    J, Jan 8, 2012
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  2. Depends on the camera, but it will either average together groups of
    pixels ("pixel binning", sometimes done to reduce noise at high ISOs on
    compact cameras) or more likely apply a resampling algorithm to downsize
    the image. However some cameras may simply crop the picture, this won't
    be possible at all zoom settings though, but it does give the illusion
    of a longer zoom at lower megapixel settings.
    Gordon Freeman, Jan 9, 2012
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  3. J

    mike Guest

    Digital zoom is quite different as it reduces the viewed area whereas
    image size retains the area just produces a picture with fewer pixels
    and a smaller file size.

    As camera memory is cheap these days I only use the lower settings for
    things like ebay pics to save time downsizing.

    The only advantage of digital zoom over cropping an 'unzoomed' image
    that I can see is that the exposure will be more suited to the bit of
    the image you are interested in. But as most p+s cameras either use
    centre weighted focus or allow you to specify, it's not an especialy
    useful function.

    Can be useful on camera phones to get rid of unwanted background but
    many smart phones allow basic editing.

    mike, Jan 9, 2012
  4. J

    Noons Guest

    Depends highly on the camera's firmware.
    Most cameras will simply change the amount of compression that is
    performed when the image is stored as a JPG file.
    Some will actually resize the image before compressing. This is
    usually the case if the aspect ratio is changed. Most cameras though
    can't really do this on a stored image, as it involves reprocessing
    the RAW image. I can only recall Olympus Pen series as the only one
    capable of doing it on a stored image. Of course, I don't have
    experience of *all* cameras! And of course many cameras can do this
    (once) at original image taking time.

    You'll find that in most cases it's the amount of JPG compression
    ("quality") that is being changed.

    You'd be well advised to take images at max quality/size and then do
    the resize/compression increase/decrease yourself at a later stage.
    Noons, Jan 9, 2012
  5. J

    Alan Browne Guest

    The manual should tell you. My cameras don't do this.

    Probably by re-sampling the sensor image size down (just like re-sizing
    a photo in an photo editor).

    This reduces resolution while (depending on the resizing algorithm) may
    reduce the appearance of noise and poor focus. Since it limits
    display/print size, the depth-of-field appears deeper than it would if
    the image were shown larger.

    A smaller stored size limits how large you can print that image later
    w/o suffering quality loss. If all you do is web/facebook pages and the
    like, then a 1 MP image is more than enough. But if you want to print
    8x10's, then you should store at least 5 MP to get a useable end
    product. And if you need to crop first, then an even larger original.
    Alan Browne, Jan 11, 2012
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