Scan DPI Vs. Print DPI

Discussion in 'Photography' started by Pat Ziegler, Jul 5, 2005.

  1. Pat Ziegler

    Pat Ziegler Guest

    There seems to be much confusion on this subject. Here is my take on it.

    Most important, Scan DPI and Print DPI are two totally separate things, (I
    think this is what confuses most people)

    Scan DPI refers to how many dots/inch of negative or slide your scanner
    will record. The larger this number the larger your output file will be and
    the larger you will be able to print.

    Misconception.... resolution = quality

    Not necessarily true. (quality will be better if you print it large) If
    you try to print a 2MP image 36inches wide you may not be happy with the
    reults... So, High Res. = ability to print large.

    If you are going to print small, 3X4, 5X7 Etc. No need to scan at high
    input DPI or use your digital cameras highest resolution.

    Print DPI

    This is the number of dots your printer will make per inch of paper.
    Normally a number like 2400.

    Normally your printer will use several "Printed" dots to make one pixel of
    your image. Eg.. printing at 300DPI using a 2400dpi printer will result in
    8 printed dots per pixel...

    I think many get confused here (why do I need a 2400dpi printer when I am
    being told I only need to print at 300dpi)

    The magic number (300dpi)

    Output resolution is totaly image dependant! No need to print higher than
    300dpi because that is all you can see. However, you may be able to printe
    at lower resolutions depending on the image and what kind of quality you
    want... I have seen fine art ink jet prints that where printed at 80dpi and
    they looked just fine. Totaly depends the amount of detail in the image.

    Film Vs. Digital

    This is one advantage film has over digital.. You don't have to worry about
    file size in the feild. You will determin that when you scan.

    My 5400 dpi scanner will make a 44Mp image file of a 35mm slide.. This
    image is 8100 pxls wide and will print 27 inches wide at 300dpi

    The math

    35mm slide is roughly 1.5 X 1 inches

    So, 5400dpi X 1.5 = 8100pxcls
    5400dpi X 1 =5400
    8100 X 5400 = 43.7 Meg.

    43.7Meg/300dpi = 27inches (aprox)

    I hope think clears thing up rather than making it more confusing..

    If I screwed up feel free to make corrections...

    Pat Ziegler
    Pat Ziegler, Jul 5, 2005
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  2. Pat Ziegler

    Scott W Guest

    A good write up but just one small point, it gets pretty complicated
    when we start to take about the number of dots printed / pixel. The
    dither routines that printers use don't use a giving number of dots /
    pixel. A result of this is that high contrast edges will show more
    detail and low contrast areas will be spread out over more dots, this
    is a good compromise since the eye does not see low contrast detail
    well any way.

    The other point is that the printer that print to photographic paper,
    like the Fuji Frontier, print at a lower number of dots / inch but each
    of the dots gets a R G and B level, not just on or off like a ink jet

    A good ink jet printer will show a bit more detail past 300 DPI, but it
    take good eyes to see it, or perhaps bad eyes, I am very near sighted
    and so I have an easier time see this fine detail then someone who is
    not near sighted.

    Scott W, Jul 5, 2005
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  3. Pat Ziegler

    Pat Ziegler Guest

    Thanks for your input Scott!
    Pat Ziegler, Jul 5, 2005
  4. Pat Ziegler

    grolschie Guest

    So what is the difference between 300dpi and my Canon ip5000 printer's specs
    of 9600x2400dpi?
    Is that overkill? I saw a huge difference in print resolution between
    300x300dpi and 720x720dpi on my old crappy Epson years ago. Even 720x720dpi
    looks like crap.

    grolschie, Jul 5, 2005
  5. Pat Ziegler

    Pat Ziegler Guest


    Generally, your printers DPI rating is the number of dots per inch your
    printer can make
    Your cannon can make 9600 dots in one inch. the 2400 number is the
    mechanical resolution which I do not totally understand so I will not try to

    So, when you print an image at 300 dpi, you printer will use 9600 dots
    to render the 300 pixels in one inch of paper...

    The larger your printer's resolution the more accurately it can render
    each pixel...

    Make sense?

    This can be more complicated, I have simplified to an extent but
    generally that is what is going on...

    Pat Ziegler, Jul 5, 2005
  6. Pat Ziegler

    grolschie Guest

    Thanks for that. So do people really mean in relation to digital images a
    print res of 300ppi? As opposed to 300dpi?
    grolschie, Jul 5, 2005
  7. Pat Ziegler

    Pat Ziegler Guest

    Yes, Same thing. pixels per inch or dots per inch. I think ppi is a more
    accurate term plus makes it less confusing because printers are rated in

    You must also consider the size of the image when printing. You can tell
    you print driver to print a 800pxl image 24 inches wide and it will do it
    but at about 30ppi. If the image had any detail in it at all it will look
    bad on paper.

    Pat Ziegler, Jul 5, 2005
  8. Pat Ziegler

    chrlz Guest

    There seems to be much confusion on this subject.
    Very true...
    Well, you are not helping by using 'dpi' when referring to scanning.
    If you check around a bit more, you will see that a lot of folk, me
    included, would like to see the term 'dpi' *avoided* when referring to
    *image* resolution and scanning, as it has been terribly misused in
    regard to printing. Use PPI (pixels per inch) or even SPI (samples per
    inch) instead. But I'm guilty of using 'dpi' by habit too.. If you
    refer to a pixel, then most people will recognise you mean one discrete
    image segment, rather than 'dot' which is often confused with a single
    colored inksplot, or perhaps just a red glowing dot on a screen (that
    of course needs a couple more to actually represent a real pixel)..
    PPI !!!
    PIXELS per inch !!!
    Up to the *optical* resolution limit of the scanner. Many scanners
    confuse the issue further by offering higher, but interpolated,
    Not a misconception. It's just *one* part of the quality equation.
    True, but as you point out later, if it is a soft focus portrait (and
    there are other types of images that enlarge extraordinarily well), you
    may be surprised... (O:
    Yes, but again, it depends on other factors like that image content
    Woah there!! What if your camera is a 1.2 Mp? What if you are
    scanning a negative? To get a good 5x7 off a neg you will need quite
    high scanning resolution (at least compared to that required if you
    were scanning a print. It depends on too many factors to make such
    True. And in fact because of the way printer manufacturers misuse the
    'dpi' specification, it is almost best to try and ignore it! Just work
    on the basis that the higher the dpi specification of the printer,
    *probably* (all other things being equal and they usually aren't!), the
    better and smoother the image will appear.
    Hmm. I disagree, although for most images that is correct, and it's a
    useful ballpark figure. But try printing a highly detailed image at
    300 and 600 (providing your printer has at least 4800 'dpi'!!) and
    compare carefully. Also, black and white images can often benefit from
    exceeding the 300 limit..
    Apart from image content, the viewing distance is important too. If
    it's a poster that will always be viewed from several feet back, then
    300 ppi printing is just be a waste of pixels..
    ...AND the viewing distance... (O:

    Well, you still need to pick a film that supports the resolution you
    will be scanning at, or the final print size. If you are shooting
    landscapes to be printed at 11x8 or larger, then Fuji 800 should not be
    your choice...
    Huh? I don't mean to nitpick, but.. 5400 x 1.4" equals about 7650
    It's actually 1.4" x 0.9". It's not a big deal, but the error gets
    bigger as you go on..
    5400ppi x 1.4" = 7650 pixels wide
    5400ppi x 0.9" = 5100 pixels high
    7650 x 5100 = 39.1 Megapixels
    Huh? It's actually the width in pixels divided by the ppi, so it's:
    7650 pixels / 300 ppi = 25.5"
    Well, with the additions above, maybe... (O;
    You did ask for it!
    chrlz, Jul 6, 2005
  9. Pat Ziegler

    Pat Ziegler Guest

    Lol... Yes I did... I admit to generalizing..... Thanks for the finising
    Pat Ziegler, Jul 6, 2005
  10. Pat Ziegler

    Pat Ziegler Guest

    Most scanner manufactures refer to it in DPI however wrong But yes PPI is
    better termnology
    We get it!!!
    Okay allready !!!
    Is a "Misconception" over used by marketing pukes...
    Define quality, we havent even started talking about composition

    Okay now you are just being argumenitive... Generaly, Generaly, Generaly!!!
    Don't go buy a 2MP camera and think your going to shoot posters cause most
    of the won't work out.. Size does matter.

    If you chase down every "What if" you get the point across. It all
    Generalities... Every rule in photography has exceptions
    Okay! These are rule to go buy not to live buy!!
    Again it's a general rule and one you should know! providng this and maybe
    that and so on and so forth doesn't help sombody who is struggling to
    understand the basics. you are muddying the waters!

    Please read above ......

    Yes, but in the field you won't be worried about it. You can spend you time
    taking picture and mind can be free to think creativly

    It's a conceptual, you missed the word, "roughly"

    You just took a general idea and made it hyper techie.. I liked it, but
    many new to the concept are now banging their heads against the wall..
    Yes I did!
    Pat Ziegler, Jul 6, 2005
  11. Pat Ziegler

    chrlz Guest

    Just as a general comment (grin), I would have to ask - have you done
    much teaching? I've now taught over a hundred photography classes, and
    most of those classes were targetted at beginners to all this
    new-fangled digital stuff. And in every aspect no matter what route
    you take, if you leave important stuff out, they (or you) will be
    bitten by it later. And here, you are posting this in a general - and
    often high-tech - forum, as information that may be relied upon by
    someone - so I think I have a right to add provisos and point out
    generalisations. And even more, if your calculations are *wrong*, you
    are simply not setting a good example. I'm sorry to be harsh, but
    aren't you the same person who is selling tutorials? I'm certainly not
    interested in paying for what is quite freely available information..
    *unless* yours is especially good and accurate and comprehensive...

    I agree, and that's pretty much what I said. But the fact that you
    didn't use the 'ppi' terminology right from the start, nor even mention
    it, suggests you may not have done much homework. Hang around in
    scanning circles for a while, and you will drop the habit quickly...
    I know, I was being the Devil's Advocate here and just trying to make
    sure *nobody* misses the point. Plleeeaaaasssse use PPI!
    No, and we haven't mentioned the subject matter, the lighting .. I
    thought your subject title was Scan DPI Vs. Print DPI? That seems to
    narrow the use of the term 'quality' quite a bit..
    Here I am just adding a fairly important proviso. Why? I'm glad you
    asked..! It's because I am sometimes taken to task by folk who tell me
    they have a 1/2/3 Megapixel camera, and that they have enlarged an
    image to a huge print that looks wonderful, and so all this stuff about
    needing 6/8/12 Mp for anything above 11x8 is just overkill. I then
    have to ask them - was this picture a portrait, or was it a detailed
    landscape? It is easy to be fooled into thinking your camera is
    capable of huge enlargements if all you have tried is, say, a close up
    portrait, for example. I have, I confess, got a bit sick of having to
    go over this issue repeatedly, and sometimes I may point it out too
    aggressively, or when it isn't required - I apologise.

    All you had to do is add 'If you are scanning prints, there is..' to
    your 'No need to scan at high input dpi...'. But you said 'No need..'
    which sounds definitive and final, and it is neither. If you want to
    simplify, then explain your parameters first. It won't confuse them if
    you keep it simple, and if you don't your audience will take away one
    of those horrid misconceptions..
    You used that 'No need..' imperative again. Yet the 300 ppi figure is
    very abitrary. Can you justify that specific number, when in fact very
    'good' prints can be had at 200 or 240? Or that the eye can in fact
    detect much higher resolutions? It is by no means a 'rule', and I
    don't see how suggesting that people should try other resolutions, and
    that image content may again be a factor, is 'muddying the waters'. I
    think you are underestimating your audience..

    Again, *you* said 'Totaly' (sic). It is definitely *not* 'totaly'.
    Semantics maybe, but you can't have it both ways.
    Personally, I think shooting at less than your camera's full-resolution
    is a dangerous and potentially embarrassing pastime, but I'll agree
    that not everyone's shooting style is the same, so I'll happily concede
    that one.
    You are clearly inviting people to look at the maths, but it was
    *wrong*. Firstly, the difference between 43.7 Meg. (sic) and 39.1 Mp
    is a fair jump - you should know that if you are quoting numbers to a
    decimal place, there will be an expectation of them being accurate to
    at least the nearest full digit. And that last calculation is *wrong*.
    '43.7 Meg' divided by 300dpi is the number of pixels in an *area*,
    being divided by a *linear* resolution and it does not give 27" no
    matter what!! That's not a 'roughly' problem, it's a completely wrong
    equation to determine an image width. Up above you accused me of
    'muddying the waters' but here you have used the *wrong* equation...
    Think about it. I should just ignore it, because it's a 'concept'????
    Sheesh. The first thing I learnt as an educator is that you *must*
    admit when you stuff things up, and accept that you will always be
    learning as you go.

    Well, forgive me if I let the *audience* decide. Please don't speak
    for the 'many', unless they voted you spokesperson. You will get
    delusions of grandeur that way.

    Anyone else reading all this, confused by my 'hyper techie' stuff? If
    so, I shall refrain from further comment.
    chrlz, Jul 6, 2005
  12. Pat Ziegler

    Scott W Guest

    Well I have to note that every scanner manufacturer seems to be using
    dpi. And all the reviews that I have seen have used dpi. Now its use
    may not be right but none the less it is what is used when taking about
    scanner resolution, at least outside the world of the new groups.

    It would have been better if ppi had become the standard,but it did not
    and we will be living with that for a long, long time to come.

    Scott W, Jul 6, 2005
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