Resolution / compression question

Discussion in 'Digital Photography' started by Dan Bjarnason, Aug 26, 2003.

  1. With the Canon S40, what's the difference between compression and
    resolution? Are these two concepts related?

    Does one of them refer to the size of the file and the other refer to
    the quality of the picture (e.g. detail, color etc).

    I just can't understand how resolution and compression are related.

    Thanks
    Dan Bjarnason, Aug 26, 2003
    #1
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  2. Dan Bjarnason

    Tom Thackrey Guest

    On 26-Aug-2003, Dan Bjarnason <> wrote:

    > With the Canon S40, what's the difference between compression and
    > resolution?


    Resolution is the size of the image. It is usually measured in pixels, for
    example 640x480 pixels. In a film camera it would be the size of the
    negative. Larger images make it easier to make larger prints that look good.
    They also take more space on your memory card.

    Compression is a technique for reducing the size of the image FILE, not the
    size of the image. The compression you refer to is probably JPEG compression
    which achieves small file sizes by discarding some information from the
    original image. This is called lossey compression. In cameras it is usually
    described in terms of quality (SHQ - super high quality, HQ - high quality,
    SQ - standard quality) or compression factor (High, Medium, or Low
    compression). The more you compress a JPEG image the smaller the file gets
    and the more informaiton is discarded.

    Are these two concepts related?

    no

    >
    > Does one of them refer to the size of the file and the other refer to
    > the quality of the picture (e.g. detail, color etc).


    Not really. See above.

    File size is often used as a measure of image size. A 6 megapixel image
    would create an 18 megabyte (6x3) uncompressed file. An 18MB uncompressed
    image file contains a larger image than a 12MB uncompressed image file.

    File size can also be used to describe compression. A 6MP image (18MB)
    compressed into a 1MB file would have 18:1 compression. A 6MP image in a 3MB
    JPEG file has less loss (AKA compression artifacts) than a 1MB JPEG of the
    same image.

    >
    > I just can't understand how resolution and compression are related.


    They aren't.


    --
    Tom Thackrey
    www.creative-light.com
    Tom Thackrey, Aug 26, 2003
    #2
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  3. Dan Bjarnason

    Patrick L. Guest

    "Dan Bjarnason" <> wrote in message
    news:...
    >
    >
    > With the Canon S40, what's the difference between compression and
    > resolution?


    See below

    >Are these two concepts related?


    No.


    >
    > Does one of them refer to the size of the file and the other refer to
    > the quality of the picture (e.g. detail, color etc).


    Resolution is the number of pixels per square inch, sometimes refered to as
    DPI or PPI. Compression will reduce file size, and introduce artifacts if
    it is not lossless compression.


    > I just can't understand how resolution and compression are related.



    They are not related.

    Patrick
    Patrick L., Aug 27, 2003
    #3
  4. Dan Bjarnason

    Guest

    In message <>,
    Dan Bjarnason <> wrote:

    >With the Canon S40, what's the difference between compression and
    >resolution? Are these two concepts related?
    >
    >Does one of them refer to the size of the file and the other refer to
    >the quality of the picture (e.g. detail, color etc).
    >
    >I just can't understand how resolution and compression are related.


    Resolution of an image file simply refers to the number of pixels in the
    file, like 2560*1920, or 1280*960, etc. Compression has to do with how
    the pixels are stored in the file. No compression at all involves
    nothing more than storing the picture as a grid of data. Lossless
    compression looks for pattern or repetition in an image, to avoid
    storing redundant information, but the picture has all its original
    detail when you view it. Lossy compression, which is what you get when
    you save in the JPEG format, loses some of the finer detail in a picture
    to make the file smaller, and when you view the picture after
    compression, it has some detail missing. With low compression, you
    might not see the difference. With heavy JPEG compression, the picture
    starts to look like a bunch of 8*8 pixel tiles with water-waves insides
    them. You will also get halos around sharp edges. Compression does not
    affect the number of pixels; no matter what compression is used, the
    number of pixels remains unchanged.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    , Aug 31, 2003
    #4
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