best compression for saving photos in jpeg?

Discussion in 'Digital Photography' started by Brian, Dec 22, 2004.

  1. Brian

    Brian Guest

    What is the best compression (1 - 100%) to use when saving a scanned
    colour photo in jpeg?
    I was to be able to display the photo on the computer screen and also
    be able to print the saved photo on a inkjet printer.

    If I have very little compression then the saved photo file size is
    too big in size. Is there a general rule I can use to decide the best
    compression to use?

    Regards Brian
     
    Brian, Dec 22, 2004
    #1
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  2. Brian

    imbsysop Guest

    0% .. :) jpg being a "lossy" compression every compression factor
    applied will degrade picture quality ... so you will have to balance
    between picture size and stored/needed/expected quality ..
    (Paintshop pro 9 has a nice (save_as/optimizer) feature that will show
    you picture deterioration versus compression factor applied ... )
    FWIW
     
    imbsysop, Dec 22, 2004
    #2
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  3. You need to determine this for yourself - what is acceptable to one person
    may not be to another. Printing is likely to require a higher quality of
    image than display on the computer screen (as the screen is limited to
    about 1MP and your scan is likely to be more than that). You also need to
    be sure that you are scanning to a sufficient number of pixels per inch.

    David
     
    David J Taylor, Dec 22, 2004
    #3
  4. Brian

    dylan Guest

    I tend to use:

    For best quality printing or editting later 1 to 5% (assuming you need to
    save space and do not want to use TIFF etc)
    For viewing on PC or 'general' printing 10%
    For internet 15 to 25 %
     
    dylan, Dec 22, 2004
    #4
  5. Brian

    Bruce Lewis Guest

    It sounds like the compression factor in the program you're using is
    reversed from the -quality switch in the cjpeg program I use, so switch 0%
    and 100% in the information below, from cjpeg's manual page.

    I personally find quality 75 to work well even with photos that have
    lots of high-contrast transitions.

    The -quality switch lets you trade off compressed file size against
    quality of the reconstructed image: the higher the quality setting, the
    larger the JPEG file, and the closer the output image will be to the
    original input. Normally you want to use the lowest quality setting
    (smallest file) that decompresses into something visually indistin-
    guishable from the original image. For this purpose the quality set-
    ting should be between 50 and 95; the default of 75 is often about
    right. If you see defects at -quality 75, then go up 5 or 10 counts at
    a time until you are happy with the output image. (The optimal setting
    will vary from one image to another.)

    -quality 100 will generate a quantization table of all 1's, minimizing
    loss in the quantization step (but there is still information loss in
    subsampling, as well as roundoff error). This setting is mainly of
    interest for experimental purposes. Quality values above about 95 are
    not recommended for normal use; the compressed file size goes up dra-
    matically for hardly any gain in output image quality.

    In the other direction, quality values below 50 will produce very small
    files of low image quality. Settings around 5 to 10 might be useful in
    preparing an index of a large image library, for example. Try -quality
    2 (or so) for some amusing Cubist effects. (Note: quality values below
    about 25 generate 2-byte quantization tables, which are considered
    optional in the JPEG standard. cjpeg emits a warning message when you
    give such a quality value, because some other JPEG programs may be
    unable to decode the resulting file. Use -baseline if you need to
    ensure compatibility at low quality values.)
     
    Bruce Lewis, Dec 22, 2004
    #5
  6. Brian

    dylan Guest

    My figures are from PSP where 1 is highest quality and goes down to 100
    which is highest compression.
     
    dylan, Dec 22, 2004
    #6
  7. Brian

    Jim Guest

    "Best" with respect to what?
    "Best quality" = least amount of compression
    "Best size" = most amount of compression.
    Most people select a medium compression value, and that might be OK for you
    provided that you do not edit the image very many times.
    Jim
     
    Jim, Dec 22, 2004
    #7
  8. Brian

    Ron Hunter Guest

    Use the minimum compression that will give you the file size you need
    for your purpose. The more you compress, the more data you lose.
    Always save the original. Remember, HD space is something like $.50US a
    gigabyte these days, so adding HD space is a pretty cheap alternative.
     
    Ron Hunter, Dec 23, 2004
    #8
  9. Brian

    Jürgen Eidt Guest

    I can second that.
    And 95% quality level really gives you the optimal value to start with.
    A 100% doesn't scale to the gain you get for quality and everything less is
    covered by the 50 cent/GB (nice value BTW ;) )
     
    Jürgen Eidt, Dec 23, 2004
    #9
  10. Brian

    Ron Hunter Guest

    Yes, considering that only a very few years ago, a 1GB HD cost $2200!!!!
    Amazing!
     
    Ron Hunter, Dec 23, 2004
    #10
  11. Brian

    Bruce Lewis Guest

    I agree that you should always save the original. However, isn't that
    50cent number ignoring the time/money required to keep things backed up?
     
    Bruce Lewis, Dec 23, 2004
    #11
  12. Brian

    Brian Guest

    I just want to scan some camera photos that I borrowed.
    I may not have access to the photos again as they will be sent
    overseas, so I need a good scan job.

    Regards Brian
     
    Brian, Dec 24, 2004
    #12
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