Jpeg question....

Discussion in 'Digital Photography' started by Paul Laup, Jan 21, 2005.

  1. Paul Laup

    Paul Laup Guest

    Hi all,

    Newbie question, I've googled to no avail.

    I'm having difficulty figuring out the whole jpegs, compression and
    resolution thing. I'm trying to cut down my images to a max of 50kb (for
    ebay incidently) keeping as much quality as possible. When I re-crop and
    save or reduce image size slightly, the resorting file ends up larger than
    it was in the first place. I can't understand it.

    Is there a program that allows you to set a maximum file size before
    adjusting the image characteristics.

    Any advice welcome.

    Cheers,

    Paul
     
    Paul Laup, Jan 21, 2005
    #1
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  2. Paul Laup

    Alan Meyer Guest

    B&B Musmon wrote:
    > >I'm having difficulty figuring out the whole jpegs, compression and
    > >resolution thing. I'm trying to cut down my images to a max of 50kb

    (for
    > >ebay incidently) keeping as much quality as possible. When I re-crop

    and
    > >save or reduce image size slightly, the resorting file ends up

    larger than
    > >it was in the first place. I can't understand it.
    > >
    > >Is there a program that allows you to set a maximum file size before
    > >adjusting the image characteristics.

    >
    > ... After you
    > have resized, which will take you a long way toward your goal you
    > then need to compress the file. Normally this is accomplished by

    just
    > saving it as a JPG and then choosing a percentage of compression.
    > Where the larger the number up to 100% will yield the best resolution
    > and the largest file. I find that 93% works pretty well.


    Very good, free software to do what you need is Irfanview. Google for
    it and download it from the Internet. Notice the Ebay checkboxes in
    the install which may or may not be desirable for you to leave checked.

    As Barry suggested, your first task is to resize/resample the image.
    That reduces the dimensions of the image - making the same picture
    smaller.

    Then you need to write it out with "Save As", setting the "quality"
    setting. One qualification to what Barry said is that the
    "percentages" aren't physical size percentages. 100 doesn't means no
    change in the byte count, and 50 doesn't mean half as many bytes. The
    numbers in all JPEG applications are arbitrary quality settings and
    you'll need to experiment with them to get the tradeoff of size and
    quality that you want. If someone used, say, "90" in one application,
    that may actually translate to 95, 85, or even 60 in some other
    application. So you have to experiment.

    Also, if your image came from a digital camera, be sure to tell
    Irfanview to NOT include the EXIF data in the Save As file. The EXIF
    can add 8-10K bytes that is of no use for an Ebay picture.

    To my knowledge, none of the JPEG compression programs allow you to set
    a maximum output size, and they couldn't easily do it because the JPEG
    algorithms don't know what the output size will be until they've
    actually compressed the data. So I repeat, you've got to experiment.
    Alan
     
    Alan Meyer, Jan 21, 2005
    #2
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  3. Paul Laup

    Ben Thomas Guest

    Paul Laup wrote:
    > Hi all,
    >
    > Newbie question, I've googled to no avail.
    >
    > I'm having difficulty figuring out the whole jpegs, compression and
    > resolution thing. I'm trying to cut down my images to a max of 50kb (for
    > ebay incidently) keeping as much quality as possible. When I re-crop and
    > save or reduce image size slightly, the resorting file ends up larger than
    > it was in the first place. I can't understand it.
    >
    > Is there a program that allows you to set a maximum file size before
    > adjusting the image characteristics.
    >
    > Any advice welcome.
    >
    > Cheers,
    >
    > Paul
    >
    >


    You want to set the dimensions (pixels wide x pixels high) based on the amount
    of screen space you want to use for the image, then set the compression to get
    the file down to the size you want. A big image will be 800x600, and thumbnails
    might be 120x90. 80% quality will look as good as 100% quality, but may still
    result in 200k files. Try 50% or 60% quality.

    --
    --
    Ben Thomas - Software Engineer - Melbourne, Australia

    My Digital World:
    Kodak DX6490, Canon i9950, Pioneer A05;
    Hitachi 37" HD plasma display, DGTEC 2000A,
    Denon 2800, H/K AVR4500, Whatmough Encore;
    Sony Ericsson K700i, Palm Tungsten T.

    Disclaimer:
    Opinions, conclusions, and other information in this message that do not
    relate to the official business of my employer shall be understood as neither
    given nor endorsed by it.
     
    Ben Thomas, Jan 21, 2005
    #3
  4. Alan Meyer commented courteously ...

    > To my knowledge, none of the JPEG compression
    > programs allow you to set a maximum output size,
    > and they couldn't easily do it because the JPEG
    > algorithms don't know what the output size will be
    > until they've actually compressed the data.


    Not really. Paint Shop Pro's JPEG Optimizer will show you
    the compressed file size in real time as you adjust the 1-
    100 compression factor.

    --
    ATM, aka Jerry
     
    All Things Mopar, Jan 21, 2005
    #4
  5. Paul Laup

    Hunt Guest

    In article <>,
    says...
    >
    >>I'm having difficulty figuring out the whole jpegs, compression and
    >>resolution thing. I'm trying to cut down my images to a max of 50kb (for
    >>ebay incidently) keeping as much quality as possible. When I re-crop and
    >>save or reduce image size slightly, the resorting file ends up larger than
    >>it was in the first place. I can't understand it.
    >>
    >>Is there a program that allows you to set a maximum file size before
    >>adjusting the image characteristics.

    >
    >
    >For most photos suitable for ebay, a 50kb file will be plenty of
    >resolution. This is usually a two step process, first you have to
    >resize the file, this isn't just cropping but changing the actual
    >dimensions of the photo. Every software package will have a feature
    >that resizes the photo. I would think that dimensions somewhere in
    >the area of 600X400 more or less will work pretty well. After you
    >have resized, which will take you a long way toward your goal you
    >then need to compress the file. Normally this is accomplished by just
    >saving it as a JPG and then choosing a percentage of compression.
    >Where the larger the number up to 100% will yield the best resolution
    >and the largest file. I find that 93% works pretty well for web pages
    >and probably will work pretty well for Ebay. From there you can make
    >minor adjustments as needed to get a good trade off between quality
    >and the size of the file. Once you have done this once or twice it
    >will become very easy for you.
    >
    >I hope this helps.
    >
    >Thanks
    >Barry


    One adjunct to Barry's suggestion. When doing the re-sizing, monitors can not
    deal with much beyond 120ppi, so you don't want your 600x400 to have a ppi of
    300, or more, 120 will be better than most monitors can handle, though that
    figure is creeping up.

    Hunt
     
    Hunt, Jan 21, 2005
    #5
  6. Paul Laup

    Jürgen Eidt Guest

    "Alan Meyer" <> schrieb
    > To my knowledge, none of the JPEG compression programs allow you to set
    > a maximum output size, and they couldn't easily do it because the JPEG
    > algorithms don't know what the output size will be until they've
    > actually compressed the data. So I repeat, you've got to experiment.


    In cPicture you can set the final file size in KB.
    You either set the quality levels or the pixel size to a fixed value.
    For web pictures you can also set the chrominance level to about 50 and the
    luminance level to 80-90.
     
    Jürgen Eidt, Jan 21, 2005
    #6
  7. Paul Laup

    B&B Musmon Guest

    >I'm having difficulty figuring out the whole jpegs, compression and
    >resolution thing. I'm trying to cut down my images to a max of 50kb (for
    >ebay incidently) keeping as much quality as possible. When I re-crop and
    >save or reduce image size slightly, the resorting file ends up larger than
    >it was in the first place. I can't understand it.
    >
    >Is there a program that allows you to set a maximum file size before
    >adjusting the image characteristics.



    For most photos suitable for ebay, a 50kb file will be plenty of
    resolution. This is usually a two step process, first you have to
    resize the file, this isn't just cropping but changing the actual
    dimensions of the photo. Every software package will have a feature
    that resizes the photo. I would think that dimensions somewhere in
    the area of 600X400 more or less will work pretty well. After you
    have resized, which will take you a long way toward your goal you
    then need to compress the file. Normally this is accomplished by just
    saving it as a JPG and then choosing a percentage of compression.
    Where the larger the number up to 100% will yield the best resolution
    and the largest file. I find that 93% works pretty well for web pages
    and probably will work pretty well for Ebay. From there you can make
    minor adjustments as needed to get a good trade off between quality
    and the size of the file. Once you have done this once or twice it
    will become very easy for you.

    I hope this helps.

    Thanks
    Barry
     
    B&B Musmon, Jan 21, 2005
    #7
  8. Paul Laup

    Martin Brown Guest

    Paul Laup wrote:

    > Hi all,
    >
    > Newbie question, I've googled to no avail.
    >
    > I'm having difficulty figuring out the whole jpegs, compression and
    > resolution thing. I'm trying to cut down my images to a max of 50kb (for
    > ebay incidently) keeping as much quality as possible. When I re-crop and
    > save or reduce image size slightly, the resorting file ends up larger than
    > it was in the first place. I can't understand it.
    >
    > Is there a program that allows you to set a maximum file size before
    > adjusting the image characteristics.


    You tend to get poor results by aiming for a fixed file size. JPEG
    compression is very data dependent. Several JPEG optimisers will show
    you in realtime what the JPEG file would look like and how long it would
    take to download on a 56k dialup.

    I quite like JPEG Optimiser for this since it also allows regions of
    interest to be less compressed than the flat backgrounds.

    PSPro 8+ also has a realtime image optimiser wizard but is not as good.

    Be sure to size the picture for the destination rectangle. No point
    having an 800x600 image displayed in an 80x60 box!

    A rough JPEG quality setting of either 20 or 80 out of 100 depending on
    the convention used by your software is a fair starting point.

    Regards,
    Martin Brown
     
    Martin Brown, Jan 21, 2005
    #8
  9. Martin Brown commented courteously ...

    [snip]
    > I quite like JPEG Optimiser for this since it also
    > allows regions of interest to be less compressed than
    > the flat backgrounds.
    >
    > PSPro 8+ also has a realtime image optimiser wizard
    > but is not as good.

    [snip]

    I've found PSP 8 and 9's JPEG Optimizer an extremely
    valuable asset, and one that I've never had a problem with
    so long as I keep the compression factor reasonable.

    > A rough JPEG quality setting of either 20 or 80 out
    > of 100 depending on the convention used by your
    > software is a fair starting point.


    I always re-open my just-saved JPEGs to be sure there're
    no artifacts or any other kind of image degradation. And,
    for all of my pictures, I find that 15 is about the
    highest compression I can go without seeing artifacts.
    Sometimes I have to go to 18 or so to get the file size
    reasonable, but seldom

    --
    ATM, aka Jerry
     
    All Things Mopar, Jan 21, 2005
    #9
  10. Paul Laup

    HRosita Guest

    Hi,

    In Irfanview, (a free image viewer that you can download from
    www.irfanview.com)
    you can specify the picture size you ultimately want like 1024x768, 800x600,
    etc. Just go to Image > Resize/Resample and choose your size.
    Just don't forget to save the picture.
    Rosita
     
    HRosita, Jan 21, 2005
    #10
  11. On Thu, 20 Jan 2005 19:52:19 -0600, All Things Mopar
    <> wrote:

    >Alan Meyer commented courteously ...
    >
    >> To my knowledge, none of the JPEG compression
    >> programs allow you to set a maximum output size,
    >> and they couldn't easily do it because the JPEG
    >> algorithms don't know what the output size will be
    >> until they've actually compressed the data.

    >
    >Not really. Paint Shop Pro's JPEG Optimizer will show you
    >the compressed file size in real time as you adjust the 1-
    >100 compression factor.


    It will either (a) be guessing at the size, in which case it will sometimes
    get it wrong, or (b) performing the compression and then telling you the
    size.

    Regards,
    Graham Holden (g-holden AT dircon DOT co DOT uk)
    --
    There are 10 types of people in the world;
    those that understand binary and those that don't.
     
    Graham Holden, Jan 21, 2005
    #11
  12. Paul Laup

    bob Guest

    "Alan Meyer" <> wrote in news:1106270539.188098.325190
    @f14g2000cwb.googlegroups.com:

    > To my knowledge, none of the JPEG compression programs allow you to set
    > a maximum output size, and they couldn't easily do it because the JPEG
    > algorithms don't know what the output size will be until they've
    > actually compressed the data. So I repeat, you've got to experiment.
    >


    Photoshop's "Save for Web" will go ahead and calculate the compression
    and give you the final file size, along with side-by-side comparisons. It
    also has an "Optimize to File Size" option, where you can tell it how
    many K to make the final file. It will only go so far though. If you have
    a 5 mp image and tell it to make it 50k, even the lowest quality settings
    result in a 142K image (for the specific image I'm looking at right now).

    For the purpose of Ebay, you don't really need to resample, because Ebay
    will do that anyway (making them much smaller than 640x480). It does save
    on upload time if you have a slow connection though.

    Bob
     
    bob, Jan 21, 2005
    #12
  13. Paul Laup

    Bruce Uttley Guest

    In article <>,
    Alan Meyer <> wrote:
    > [clip]
    >
    >To my knowledge, none of the JPEG compression programs allow you to set
    >a maximum output size, and they couldn't easily do it because the JPEG
    >algorithms don't know what the output size will be until they've
    >actually compressed the data. So I repeat, you've got to experiment.
    >Alan
    >


    Photoshop CS has an "Optimize to File Size" option in its "Save For
    Web". You enter the desired file size in "K" bytes. The "Optimize
    To File Size" window is found from the "Save For Web" window by
    clicking the round, right-pointing arrow to the right of the
    'Preset' pulldown. After entering the value, Photoshop CS tells you
    how big the file is and what compression quality value it chose.
     
    Bruce Uttley, Jan 21, 2005
    #13
  14. On 20 Jan 2005 17:22:19 -0800, "Alan Meyer" <> wrote:

    >To my knowledge, none of the JPEG compression programs allow you to set
    >a maximum output size, and they couldn't easily do it because the JPEG
    >algorithms don't know what the output size will be until they've
    >actually compressed the data. So I repeat, you've got to experiment.


    Why couldn't the program do the experimenting for you? jpegsizer allows
    you to set the size wanted; I assume it does it by trial and error.

    --
    Stephen Poley
     
    Stephen Poley, Jan 22, 2005
    #14
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