Question - Boosting DPI

Discussion in 'Digital Photography' started by Dryb66, Apr 8, 2004.

  1. Dryb66

    Dryb66 Guest

    I'm new to digital photography. If I have a JPG image from my camera (Olympus
    C-5000) at 144 dpi resolution and bump it up with Adobe to 300 dpi as a TIFF
    file am I loosing any quality?

    I've read that with each save of a JPG file there is a loss of some quality.
    What I need is the high resolution that 300 dpi provides.
    Thanks.
     
    Dryb66, Apr 8, 2004
    #1
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  2. Dryb66

    Lucas Tam Guest

    (Dryb66) wrote in
    news::

    > I'm new to digital photography. If I have a JPG image from my camera
    > (Olympus C-5000) at 144 dpi resolution and bump it up with Adobe to
    > 300 dpi as a TIFF file am I loosing any quality?


    Nope, as long as you save as a TIFF file.

    > I've read that with each save of a JPG file there is a loss of some
    > quality. What I need is the high resolution that 300 dpi provides.


    Why not set the file to 300dpi before each print? There's no real need to
    save a 300dpi TIFF version unless you're planning on doing some editing.



    --
    Lucas Tam ()
    Please delete "REMOVE" from the e-mail address when replying.
    http://members.ebay.com/aboutme/coolspot18/
     
    Lucas Tam, Apr 8, 2004
    #2
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  3. Dryb66

    Guest

    Dryb66 <> wrote:
    > I'm new to digital photography. If I have a JPG image from my camera (Olympus
    > C-5000) at 144 dpi resolution and bump it up with Adobe to 300 dpi as a TIFF
    > file am I loosing any quality?


    > I've read that with each save of a JPG file there is a loss of some quality.


    Right, but this has nothing to do with adjusting dpi. You can adjust the
    dpi setting for an image and save it either as a pds file, or tiff if you
    are using Photoshop. If you need a compressed file, you can always save a
    jpg and a pdd or tiff file. There's no reason to chose exclusively one format.
     
    , Apr 8, 2004
    #3
  4. Dryb66

    Jim Townsend Guest

    Dryb66 wrote:

    > I'm new to digital photography. If I have a JPG image from my camera (Olympus
    > C-5000) at 144 dpi resolution and bump it up with Adobe to 300 dpi as a TIFF
    > file am I loosing any quality?


    You're doing absolutely nothing to the resolution of your image...
    DPI is a printing term. Until you actually print your image
    changing the DPI is a wasted effort.

    If you look at whatever program you're using to show you DPI,
    you'll see that all DPI is, is the number of pixels (dots) in your
    image divided by the number of inches you want to print at.

    Example.. Your image is 1760 pixels (dots) wide. Your DPI shows
    as 144.. Lets figure out the size of your image if you print it.

    1760 dots / 144 dots per inch = 12.2 inches.

    In other words, if you spread your image on paper and cause every 144
    pixels in your image fill up one inch of paper.. Then the printed image
    will be 12.22 inches long. It MUST be 12.2 inches long.

    If you chage the DPI to 300 then your image will print at:

    1760 dots / 300 dots per inch = 5.86 inches

    (Try this and see).

    ALL you do when you change DPI is change the size of the *document*
    that will come out of your printer. DPI has *no* effect on the
    quality of the pixels or resolution of your image as it exists
    on your hard drive.

    All you are setting when you set DPI is a couple of bytes at the
    beginning of the file. These bytes are there because the JFIF
    standard says so.

    These bytes are read by your printer and tell it how big to print the
    image. DPI is for printing only.

    > I've read that with each save of a JPG file there is a loss of some quality.
    > What I need is the high resolution that 300 dpi provides.


    Saving JPEG files over and over will degrade your image. But again.. changing
    DPI does absolutely nothing to with the pixels in your image.. DPI only
    determines how big the image will be when you *send it to the printer*.

    The best strategy in your case is to save the original JPEG and never
    overwrite it. That way it will never degrade.
     
    Jim Townsend, Apr 8, 2004
    #4
  5. Dryb66

    Guest

    In message <>,
    (Dryb66) wrote:

    >I'm new to digital photography. If I have a JPG image from my camera (Olympus
    >C-5000) at 144 dpi resolution and bump it up with Adobe to 300 dpi as a TIFF
    >file am I loosing any quality?


    Possibly; depending on the settings you use, the image may be resampled.
    I do not resample unless the print size I want would use less than about
    200 PPI (pixels per inch, much more meaningful than DPI, since an image
    doesn't have dots the way a printer does). I will multiply the width
    and height of the image by exactly 2 or 3, as needed, to surpass 200
    PPI. I never use any non-integer values (unless they are much larger
    numbers than 2 or 3), as they destroy detail in a sharp image from a
    camera with a sharp lens.


    I view dealing with embedded DPI in general to be bad practice, unless
    you want the image to jus print quickly in the future at a fixed size,
    without any processing done to it, because that is really the only thing
    an embedded DPI is good for. I just tell the program that is doing the
    printing what size (in inches) I want the print to be; no need to deal
    with DPI.

    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    , Apr 10, 2004
    #5
  6. Dryb66

    Guest

    In message <5304840.PzCIjxSiXh@muxnet-news>,
    Jim Townsend <> wrote:

    >You're doing absolutely nothing to the resolution of your image...


    Depends on the program and the settings used. Changing DPI can
    sometimes result in resampling the image at a ratio that destroys
    detail.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    , Apr 10, 2004
    #6
  7. Dryb66

    John Navas Guest

    [POSTED TO rec.photo.digital - REPLY ON USENET PLEASE]

    In <> on Sat, 10 Apr 2004 06:48:35
    GMT, wrote:

    >In message <>,
    > (Dryb66) wrote:
    >
    >>I'm new to digital photography. If I have a JPG image from my camera (Olympus
    >>C-5000) at 144 dpi resolution and bump it up with Adobe to 300 dpi as a TIFF
    >>file am I loosing any quality?

    >
    >Possibly; depending on the settings you use, the image may be resampled.
    >I do not resample unless the print size I want would use less than about
    >200 PPI (pixels per inch, much more meaningful than DPI, since an image
    >doesn't have dots the way a printer does). I will multiply the width
    >and height of the image by exactly 2 or 3, as needed, to surpass 200
    >PPI. I never use any non-integer values (unless they are much larger
    >numbers than 2 or 3), as they destroy detail in a sharp image from a
    >camera with a sharp lens.


    Not necessarily -- that depends on the resampling algorithm.

    --
    Best regards,
    John Navas
    [PLEASE NOTE: Ads belong *only* in rec.photo.marketplace.digital, as per
    <http://bobatkins.photo.net/info/charter.htm> <http://rpdfaq.50megs.com/>]
     
    John Navas, Apr 10, 2004
    #7
  8. Dryb66

    Guest

    In message <3rNdc.4925$>,
    John Navas <> wrote:

    >[POSTED TO rec.photo.digital - REPLY ON USENET PLEASE]
    >
    >In <> on Sat, 10 Apr 2004 06:48:35
    >GMT, wrote:
    >
    >>In message <>,
    >> (Dryb66) wrote:
    >>
    >>>I'm new to digital photography. If I have a JPG image from my camera (Olympus
    >>>C-5000) at 144 dpi resolution and bump it up with Adobe to 300 dpi as a TIFF
    >>>file am I loosing any quality?

    >>
    >>Possibly; depending on the settings you use, the image may be resampled.
    >>I do not resample unless the print size I want would use less than about
    >>200 PPI (pixels per inch, much more meaningful than DPI, since an image
    >>doesn't have dots the way a printer does). I will multiply the width
    >>and height of the image by exactly 2 or 3, as needed, to surpass 200
    >>PPI. I never use any non-integer values (unless they are much larger
    >>numbers than 2 or 3), as they destroy detail in a sharp image from a
    >>camera with a sharp lens.

    >
    >Not necessarily -- that depends on the resampling algorithm.


    There's no such thing as lossless non-integer upsampling; light sampled
    uniquely to original pixels spreads out to multiple pixels, so you lose
    detail close to the original sampling's maximum frequency.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    , Apr 10, 2004
    #8
  9. Dryb66

    John Navas Guest

    [POSTED TO rec.photo.digital - REPLY ON USENET PLEASE]

    In <> on Sat, 10 Apr 2004 12:57:27
    GMT, wrote:

    >In message <3rNdc.4925$>,
    >John Navas <> wrote:
    >
    >>In <> on Sat, 10 Apr 2004 06:48:35
    >>GMT, wrote:
    >>
    >>>In message <>,
    >>> (Dryb66) wrote:
    >>>
    >>>>I'm new to digital photography. If I have a JPG image from my camera (Olympus
    >>>>C-5000) at 144 dpi resolution and bump it up with Adobe to 300 dpi as a TIFF
    >>>>file am I loosing any quality?
    >>>
    >>>Possibly; depending on the settings you use, the image may be resampled.
    >>>I do not resample unless the print size I want would use less than about
    >>>200 PPI (pixels per inch, much more meaningful than DPI, since an image
    >>>doesn't have dots the way a printer does). I will multiply the width
    >>>and height of the image by exactly 2 or 3, as needed, to surpass 200
    >>>PPI. I never use any non-integer values (unless they are much larger
    >>>numbers than 2 or 3), as they destroy detail in a sharp image from a
    >>>camera with a sharp lens.

    >>
    >>Not necessarily -- that depends on the resampling algorithm.

    >
    >There's no such thing as lossless non-integer upsampling; light sampled
    >uniquely to original pixels spreads out to multiple pixels, so you lose
    >detail close to the original sampling's maximum frequency.


    In general, the difference is not visually detectable with a good resampling
    algorithm.

    --
    Best regards,
    John Navas
    [PLEASE NOTE: Ads belong *only* in rec.photo.marketplace.digital, as per
    <http://bobatkins.photo.net/info/charter.htm> <http://rpdfaq.50megs.com/>]
     
    John Navas, Apr 10, 2004
    #9
  10. Dryb66

    Paul J Gans Guest

    wrote:
    >In message <3rNdc.4925$>,
    >John Navas <> wrote:


    >>[POSTED TO rec.photo.digital - REPLY ON USENET PLEASE]
    >>
    >>In <> on Sat, 10 Apr 2004 06:48:35
    >>GMT, wrote:
    >>
    >>>In message <>,
    >>> (Dryb66) wrote:
    >>>
    >>>>I'm new to digital photography. If I have a JPG image from my camera (Olympus
    >>>>C-5000) at 144 dpi resolution and bump it up with Adobe to 300 dpi as a TIFF
    >>>>file am I loosing any quality?
    >>>
    >>>Possibly; depending on the settings you use, the image may be resampled.
    >>>I do not resample unless the print size I want would use less than about
    >>>200 PPI (pixels per inch, much more meaningful than DPI, since an image
    >>>doesn't have dots the way a printer does). I will multiply the width
    >>>and height of the image by exactly 2 or 3, as needed, to surpass 200
    >>>PPI. I never use any non-integer values (unless they are much larger
    >>>numbers than 2 or 3), as they destroy detail in a sharp image from a
    >>>camera with a sharp lens.

    >>
    >>Not necessarily -- that depends on the resampling algorithm.


    >There's no such thing as lossless non-integer upsampling; light sampled
    >uniquely to original pixels spreads out to multiple pixels, so you lose
    >detail close to the original sampling's maximum frequency.
    >--


    All sampling, up sampling or down sampling amounts to
    plugging values into a formula. The values plugged in
    are the pixels in the starting image.

    Thus only "original" pixels are ever used.

    For example, and using a linear "sampling" function: let
    us say that we want to produce a new pixel half way between
    two existing ones. This is upsampling. How to do it?

    If p1 and p2 are the color values at two adjacent existing
    pixels, then the color value at the new pixel pn could be
    calculated as:

    pn = 1/2 (p1 + p2)

    But we can do this in general. If we want to produce
    pixels 0.453 of the way between the first two we could
    use:

    pn = 0.453 p1 + 0.547 p2

    and similarly for any other number. But note that we
    are still using "original" pixel data.

    The actual formulas used vary but are generally more
    complex. One could, for instance use a grid of 9
    pixels in the pattern:

    x x x
    x x x
    x x x

    to produce new values around the central x. One then
    moves over one row or column of pixels and repeats.
    The final image need include none of the original points
    (and won't, if an incommesurate scale factor is used),
    but the new image will use nothing but "original
    pixels."

    In my opinion, none of the current sampling routines
    are perfect. What is also needed is edge detection
    (that is, don't blur out an edge where a sharp one
    exists) and color change (don't insert a new color
    that does not exist in the original when downsizing
    and be very careful about what is done on upsizing.)

    The new world of digital photography (and it is a
    new world) requires very new techniques. Don't forget
    that some of the ones we use with film (enlarging
    or shrinking an image) have been developed over
    the last 100 years or more.

    ---- Paul J. Gans
     
    Paul J Gans, Apr 11, 2004
    #10
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