72 dpi pictures with Canon EOS 400D/Digital Rebel XTi

Discussion in 'Digital Photography' started by shaji, Sep 21, 2007.

  1. shaji

    shaji Guest

    Hi all,
    All of the pictures taken with my Canon EOS 400D/Digital Rebel XTi
    come with horizontal/vertical of just 72 dpi. The image quality I set
    is Large-Fine. The width of the pictres is 3888 pixels and hieght is
    2592 pixels.

    1. Is this the default behaviour of all Canon EOS 400D/Digital Rebel
    XTi cameras?
    2. How can I change the resolution (dpi value) of pictures on my
    camera?

    Thanks in advance.
    Shaji.
     
    shaji, Sep 21, 2007
    #1
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  2. shaji

    cmyk Guest

    No, the pitcures have no inherent print density. 72dpi is probably just the default chosen by your software in the absence of any
    metadata in the image file to suggest otherwise.
    You don't. You use your print software to print the picture at whatever size you want and it'll do whatever conversions are
    required.

    Cheers
     
    cmyk, Sep 21, 2007
    #2
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  3. shaji

    shaji Guest

    Thanks a lot cmyk :)

    I was just wondering whether my pictures (with just 72 dpi) would look
    awful if I make a print. My friends Nikon D80 images show a resolution
    of 300 dpi. This really frightened me.

    So, you mean to say that I don't need to bother about the default dpi
    value?

    Shaji.
     
    shaji, Sep 21, 2007
    #3
  4. shaji

    Bates Guest

    Hi Shaji,

    Your friends images at 300dpi then are probably smaller (in inches)
    than your images at 72dpi. They still may have the same number of
    overall pixels. In most imaging software you can "resample" the image
    to change the dpi value to whatever you want, but it will then change
    the "size" in inches of your image.

    Regardless, your 10MP shot will print fine at say 8x10 or larger.

    Bates...
     
    Bates, Sep 21, 2007
    #4
  5. shaji

    Allen Guest

    What size are the files when you download them onto your computer (int
    megabytes)?
    Allen
     
    Allen, Sep 21, 2007
    #5
  6. shaji

    Matt Ion Guest

    There is no such thing as "dpi" in a digital image file. DPI is "dots
    per inch", and there are no "inches" involved in the picture until you
    actually print it to a physical medium.

    Short answer: don't worry about it, it's only relevant when it comes
    time to print.
     
    Matt Ion, Sep 21, 2007
    #6
  7. shaji

    Good Man Guest

    yep, just make sure that in Photoshop, you do not resample the image, just
    resize it.
     
    Good Man, Sep 21, 2007
    #7
  8. shaji

    Paul J Gans Guest

    Ok. I agree. But can anyone explain something to me: I would assume
    that for an image to be printed, one wants to have as many pixels in
    the image as one can get on the printer. Yes, I know that the printer
    will adjust to what it is given, but still, I'd like to do it, not the
    printer.

    Now printers advertize all sorts of resolution. But it is never clear
    if that's "real" resolution, interpolated resolution (i.e. the printer
    interpolates no matter what it is given), or what.

    Further, I can't usually find that information on a manufacturer's web
    site.
     
    Paul J Gans, Sep 21, 2007
    #8
  9. shaji

    Good Man Guest

    As long as you're not resampling the image in Photoshop or another photo
    editor, the pixel count on your image is equal to the megapixel count of
    your photo! ie: take a photo with a Canon Rebel XT (8 MP) and you get an
    image that is 3456 pixels by 2304 pixels, for a total of (hit the
    calculator) 7,962,624 pixels in your image. Always. (until you change it).
     
    Good Man, Sep 21, 2007
    #9
  10. shaji

    Robert Coe Guest

    : Thanks a lot cmyk :)
    :
    : I was just wondering whether my pictures (with just 72 dpi) would look
    : awful if I make a print. My friends Nikon D80 images show a resolution
    : of 300 dpi. This really frightened me.
    :
    : So, you mean to say that I don't need to bother about the default dpi
    : value?

    It depends on what the meaning of the word "inch" is. You can regard the
    picture as huge but of low resolution or small and of high resolution. Until
    you tell the printer how big to make the picture and how many pixels to use to
    do it, it doesn't matter.

    Bob
     
    Robert Coe, Sep 21, 2007
    #10
  11. shaji

    Paul J Gans Guest

    I understand that. My question was to find out the actual printer
    printing density.

    For example: if the printer can only handle 300 dpi and I
    want to print on 3x5 paper the printer will downsize the
    image to 1500x900 pixels from the 3456x2304 in the original
    image.

    In that case I'd rather do the cropping and downsizing myself
    instead of letting the printer do it.

    My question is: how do I find out what the *REAL* dpi of the
    printer is? I don't necessarily believe the manufacturer's
    ads since they sometimes are the result of the printer driver
    resizing your image for you.
     
    Paul J Gans, Sep 22, 2007
    #11
  12. shaji

    dj_nme Guest

    The best way to make an inkjet print that looks as good as a photolab
    print is to not go below 200ppi (pixels per inch) and to use your
    printer manufacturer's ink and paper.
    300ppi is considered the benchmark for "photo quality", but depending on
    paper and printer may not make a difference.

    This can be checked by dividing the image size in pixels by the output
    size in inches, eg: your 3456x2304pixel jpeg/tiff/png/bmp printed at
    17.2x11.5 inches would give you a 300ppi printout.
    With modern software and inkjet printers, it is best to not resample
    (unless you're making your print so large that it will go below 200ppi),
    as printing a smaller sized printout increases the ppi and gives the
    inkjet printer more information to use when dithering the ink droplets
    across the page.

    The connection between dpi and ppi is rather circuitous:
    dpi as inkjet printer manufacturers state is the combined desinty of ink
    nozzles and how finely the printhead carriage can be repositioned (it's
    how densly the droplets can be dithered across the page to form smooth
    tone transitions), many droplets (the "d" in dpi) are required to render
    each image pixel onto paper;
    ppi is how densly the image pixels are spread across the paper and if
    you go below 200ppi, the image will sart to look pixelated (showing
    "jaggies" on sloped and curved edges in the printed picture).
    In order to print at 200ppi, your printer must have a stated resoultion
    of at least 800dpi (most modern inkjets are 2400x4800dpi), so your
    printer if it's only able to go up to 300dpi will produce very coarse
    looking results, almost as though you've used the same process as
    newspaper printing does (it's particularly bad on gradients of
    colour/tone and looks "dotty").
    If you have an old inkjet printer which proudly proclaims on the box
    something like "Able to print at an amazing 300dpi!", then it's time to
    upgrade to a modern inkjet (even the cheapest today don't have dithering
    resolution of less than 2400x4800dpi).
     
    dj_nme, Sep 23, 2007
    #12
  13. Actually, this would be 200 pixels per inch.
     
    sheepdog 2007, Sep 23, 2007
    #13
  14. shaji

    dj_nme Guest

    You're correct.
    Perhaps I shouldn't try posting things that require calculations when
    I've got a hangover? ;-)
     
    dj_nme, Sep 23, 2007
    #14
  15. shaji

    Paul J Gans Guest

    Again, I understand that. The question is: where does one
    get the information on that for most printers?
    Yes. The question is then given 2400 dpi, how many ppi is that?
    I understand this depends on the number of different colors the
    printer cartridges hold and on the actual color of the image
    pixel -- a blue corresponding to the cartridge blue should only
    require one dot while a more complex color might require six,
    if the printer has six different colors.

    The ultimate goal is to tailor the image to the paper on which
    the image is being printed while relying as little as possible
    on the algorithms in the printer (other than the color response
    curve, of course).
     
    Paul J Gans, Sep 23, 2007
    #15
  16. shaji

    dj_nme Guest

    Unfortunately, none of the inkjet printer manufacturers actually release
    that sort of information.
    My rule of thumb is to divide the dpi by number of ink carts used in the
    printer to get a rough number for an ultimate ppi figure the printer
    should be capable of.
    Whether this gets a real measure of what the printer is capable of is
    impossible to say with any certainty, testing your own printer seems to
    be the best way I can think of to find it's highest ppi output.
    Don't forget that even at 200ppi, it's unlikely that given a good image
    file that any modern inkjet printer will give you a "halftoned" (dotty
    looking) looking printout.
    If the printouts look good at 200ppi and at 300ppi, why worry about what
    the theoretical upper limit will be, as it's more likely to run up
    against the bleed limit (the amount ink will spread into it's surface,
    limiting the smallest size dot an ink droplet can form on the page) of
    even the best paper?
    Without really knowing how the dpi translates out into a highest ppi
    output (it may be different for different manufacturers that claim the
    same dpi rating for their inkjet printers), you can only use trial and
    error to determine it for tourself.
    When you print out, you're got both the paper bleed limit and the
    ultimate resolution the printer can acheive to contend with.
    Glossy paper with a modern inkjet printer may be able to acheive a
    resolution of greater than 300ppi, but using matte or textured paper may
    be limited to under 200ppi with it's bleed limit and texture (but still
    look "nice" and "photo quality" without examining it with a loupe).
    If it makes you feel better, perhaps you should downsample your printout
    to something that would acheive 200ppi or 300ppi at your desired
    printout size, so that there is enough information (but no more than
    absolutely required) for the printer to produce what is to you an
    acceptable "photo quality" printout?
     
    dj_nme, Sep 23, 2007
    #16
  17. shaji

    valjean

    Joined:
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    I'm resurrecting this old thread, because I'm still confused.

    I have the Rebel XT and want to understand all this 72 dpi, ppi, etc. etc.
    My question is this.
    I work for a magazine print industry (very new btw) and when I send off my pages, photos etc., to the printers they will not take photos below 300dpi.
    So what do I do when the camera only shoots at 72dpi?
    Do I have to go into Photoshop under Image Size and change the dpi myself?
    If I do do that, what is going to happen?
    Will the image size change?
    Will the quality of the image suffer or change at all?

    Thanks in advance......Valerie
     
    valjean, Feb 22, 2009
    #17
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