DPI vc resolution

Discussion in 'Digital Photography' started by Ilia Poliakov, Jul 14, 2003.

  1. Hi all,

    I've taken two photos in 640x480 mode and in 1024x768. The real size of the
    photos is the same (I mean the pictures are absolutletely the same), but the
    dpi is also the same (120 dpi). How can it be? What do I not understand?
     
    Ilia Poliakov, Jul 14, 2003
    #1
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  2. Ilia Poliakov

    J. A. Mc. Guest

    On Mon, 14 Jul 2003 16:59:05 +0200, "Ilia Poliakov"
    <> found these unused words floating about:

    >Hi all,
    >
    >I've taken two photos in 640x480 mode and in 1024x768. The real size of the
    >photos is the same (I mean the pictures are absolutletely the same), but the
    >dpi is also the same (120 dpi). How can it be? What do I not understand?
    >

    Define "real size" from your view.
    Monitor, print, files ???
     
    J. A. Mc., Jul 14, 2003
    #2
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  3. > Define "real size" from your view.

    "Real size" is what on the picture is. I have two totally identical
    pictures: one is 640x480 and the other is 1024x768. And in the file
    properties the image resolution is 120 dpi for both pictures.
     
    Ilia Poliakov, Jul 14, 2003
    #3
  4. Ilia Poliakov

    Tom Thackrey Guest

    On 14-Jul-2003, "Ilia Poliakov" <> wrote:

    > > Define "real size" from your view.

    >
    > "Real size" is what on the picture is. I have two totally identical
    > pictures: one is 640x480 and the other is 1024x768. And in the file
    > properties the image resolution is 120 dpi for both pictures.


    if they have different pixel dimensions they aren't identical and they will
    display as different sizes on your monitor (at 100%). Either you're confused
    about the dimensions or aren't telling us something. If you can put them on
    a web a site and post the link here it would help a great deal. If you email
    them to me I will post a link.

    --
    Tom Thackrey
    www.creative-light.com
     
    Tom Thackrey, Jul 14, 2003
    #4
  5. By definition these two images are NOT the same size in terms of pixel
    dimensions.
    If you're viewing the images on your computer monitor, whatever the dpi
    number is is quite irrelevant.
    If you're using MS Internet Explorer to look at them IE will resize the
    displayed image to fit your monitor, perhaps this is what's misleading you.

    "Ilia Poliakov" <> wrote in message
    news:beuger$972pq$-berlin.de...
    > Hi all,
    >
    > I've taken two photos in 640x480 mode and in 1024x768. The real size of

    the
    > photos is the same (I mean the pictures are absolutletely the same), but

    the
    > dpi is also the same (120 dpi). How can it be? What do I not understand?
    >
    >
     
    Richard Howes, Jul 14, 2003
    #5
  6. Ilia Poliakov

    Jim Townsend Guest

    Ilia Poliakov wrote:

    > Hi all,
    >
    > I've taken two photos in 640x480 mode and in 1024x768. The real size of the
    > photos is the same (I mean the pictures are absolutletely the same), but the
    > dpi is also the same (120 dpi). How can it be? What do I not understand?


    DPI = Dots Per INCH.. Now consider.. An inch is a PHYSICAL dimension.. It is
    something that can be *seen* and *measured*. You can't see or measure your
    image file when it's in your camera or on your hard disk.. So I'll ask you..
    When they say dots per INCH.. What does this inch refer to, where is it and
    and how would you go about measuring it ?

    When you know the answer, you shall become enlightened :)

    OK... Inch refers to an inch of PAPER.. DPI is the size your image will be
    when printed on PAPER. The term DPI has *no* meaning until your image
    actually hits the paper. As a matter of fact the DPI setting has nothing at
    all to do with the pixels in the image..

    You can change your DPI value at will.. You can type anything you want in the
    boxes.

    When you change DPI, all you are changing in your image file is a couple of
    bytes in the header.. These couple of bytes are read by your printer software
    and tell your printer how big the image will be on paper... It defines how
    many inches of length and width your image will create on paper.

    It's incredibly simple..

    If you take 1000 pixels and spread them across 10 inches you have...
    1000 pixels divided by 10 inches = 100 pixels per inch.

    It *has* to be 100 pixels per inch.. It simply can't be anything else.

    If you set a 1000 pixel image at 100 DPI, it will print at 10 inches. If you
    change the DPI to 200 dpi, then the image will print 5 inches wide.

    Now for *your* images.

    Your 640 x 480 image will print at:

    640 pixels divided by 120 dpi = 5.33 inches
    480 pixels divided by 120 dpi = 4.00 inches

    Your 1024 x 768 image will print at:

    1024 pixels divided by 120 dpi = 8.53 inches
    768 pixels divided by 120 dpi = 6.40 inches

    The software you are using will display both DPI and Inches.. Check to see if
    my figures are correct :)
     
    Jim Townsend, Jul 15, 2003
    #6
  7. Ilia Poliakov

    Don Stauffer Guest

    You mean the field of view is the same? Yes, we have beat this to death
    lately. When you change the resolution on digicams, you do not crop,
    you change sampling interval, samples per unit field angle (samples per
    degree of picture field angle. If you look closely on a high res
    printout or high res monitor you should see some difference in
    'softness'.


    Ilia Poliakov wrote:
    >
    > > Define "real size" from your view.

    >
    > "Real size" is what on the picture is. I have two totally identical
    > pictures: one is 640x480 and the other is 1024x768. And in the file
    > properties the image resolution is 120 dpi for both pictures.


    --
    Don Stauffer in Minnesota

    webpage- http://www.usfamily.net/web/stauffer
     
    Don Stauffer, Jul 15, 2003
    #7
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