100% JPEG quality ?

Discussion in 'Digital Photography' started by Alfred Molon, Jul 29, 2003.

  1. Alfred Molon

    Alfred Molon Guest

    Alfred Molon, Jul 29, 2003
    #1
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  2. Alfred Molon

    Travis Guest

    Alfred Molon wrote:
    > Can anybody explain what 100% JPEG quality means ? Perhaps that
    > the compression ratio can't be lower than that ?


    What is the context of the statment?

    --
    Travis in Shoreline Washington
    Uses a Kodak DC4800
    Travis, Jul 29, 2003
    #2
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  3. Alfred Molon

    Alfred Molon Guest

    In article <>,
    EG*nospam* says...

    > >Can anybody explain what 100% JPEG quality means ? Perhaps that the
    > >compression ratio can't be lower than that ?

    >
    > It is the highest quality setting of the given algorithm being used. From
    > program to program there is no compatibility nor consistency.


    I see. What is the lowest possible compression ratio for JPEG images ?
    --

    Alfred Molon
    ------------------------------
    http://groups.yahoo.com/group/Olympus4040_5050/
    Olympus 4040 resource - http://www.molon.de/4040.htm
    Olympus 5050 resource - http://www.molon.de/5050.htm
    Alfred Molon, Jul 30, 2003
    #3
  4. In article <>,
    says...
    > In article <>,
    > EG*nospam* says...
    >
    > > >Can anybody explain what 100% JPEG quality means ? Perhaps that the
    > > >compression ratio can't be lower than that ?

    > >
    > > It is the highest quality setting of the given algorithm being used. From
    > > program to program there is no compatibility nor consistency.

    >
    > I see. What is the lowest possible compression ratio for JPEG images ?


    You still haven't said what software you use, and as Ed Ruf said, it
    can vary between programs.

    There is a JPEG FAQ by Tom Lane around somewhere. You should be able to
    find it with Google. But anyway, a JPEG compression library
    (I've forgotten the name) commonly used by many imaging programs has 95
    as the practical maximum quality setting. It is possible to go higher,
    but then the size of the file grows very fast without adding any
    visible improvement to the the image. Remember, JPEG is *always* lossy,
    no matter how high a quality setting you use. That's why you should not
    use JPEG as an intermediary format while editing an image. Store the
    image in a lossless format such as 24-bit TIFF or PNG, and only
    compress it to JPEG when you have finished with it.

    You should look at the images yourself to decide how much they can be
    compressed, though 75 is often a starting point, if going by the common
    scale. It's a tradeoff. Increase the number, and picture quality will
    improve (up to about 95, as I said), but the file will grow bigger.

    Remember, what I've said is common, but not standardized. Paint Shop
    Pro goes the other way, with *lower* numbers meaning higher quality,
    but bigger files. Reportedly, they subtract the common number from 100,
    so that in PSP you have to set JPEG compression to 25 to get
    what is commonly known as quality setting 75, set 5 to get 95, and so
    on. I haven't been able to verify if this is exactly true, though.

    Finally, it is probably wrong to refer to the quality with the % sign,
    as it's not a percentage of anything. It's only an accident that the
    practical maximum is close to 100.

    Yngvar Følling
    Yngvar Følling, Jul 30, 2003
    #4
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