dots per inch?

Discussion in 'Digital Photography' started by eugene, Sep 19, 2007.

  1. eugene

    eugene Guest

    Someone has asked me to give them an image with 350 dots per inch. Is this
    the same as 350 pixels per inch?

    eugene, Sep 19, 2007
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  2. eugene

    Scott W Guest

    There will be no doubt another long debate about ppi vs. dpi, but yes if
    they asked for 350 dots per inch it is a very good bet that what they
    really meant was 350 pixels per inch.

    Scott W, Sep 19, 2007
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  3. eugene

    HEMI-Powered Guest

    Scott W added these comments in the current discussion du jour
    re: another long debate. I think you may be right here, Scott! As
    best I can tell, the term DPI originated in the printing industry
    for the earliest of what we now know as half-tone printing, which
    is the laying down of a pattern of "dots" in a geometrically
    regular pattern at an angle, often 45 degrees. In the days of B &
    W newspapers, the number and size of the "dots" laid down roughly
    to approximate the shades of gray in a continuous tone photo of
    the day allowed the black dots and white news print to fool the
    human eye into thinking they were looking at a real photo.

    Later, the same idea was applied to color photos.

    Much, much later, when computer scanners were invented, the term
    DPI now had real meaning, in that it specified how many "dots"
    the user wanted the scanner to "sample" or scan per linear inch
    across the paper and down its length. Each "dot" resulted in a
    pixel in the final image. AFAIK, that definition of "DPI" is
    still valid.

    I won't go into the debate about DPI for ink jet printers except
    to say that the number of "dots" laid down by the printer in
    order to "dither" to get the desired colors and density isn't at
    all the same sort of definition I used above. Yes, of course the
    printer is actually producing N DPI but it seems difficult for
    them that aren't mathematicians to understand what is really

    For us normal folk, who just want to get "good" prints from a
    given pixel resolution raster graphics image, I agree with you
    and most others in that "DPI" really means "PPI". I do not get
    any of my images printed by pro shops nor do I dabble in
    "printing" my images in publications that use today's version of
    half-tone printing, but I suppose there are places that are set
    up to calculate the finished print size using "DPI". One can
    obviously do the exact same thing using "PPI" but perhaps older
    print machines and/or older software may want DPI.

    And with that, let the debate begin!
    HEMI-Powered, Sep 19, 2007
  4. eugene

    bugbear Guest

    You didn't mention the correct units for sensor resolution ;-)

    bugbear, Sep 19, 2007
  5. eugene

    Paul Furman Guest

    There can only be one interpretation if asked for a digital file. It
    would only mean printer dot resolution if the request was for a paper print.
    Interestingly, half-tone requires a huge resolution in digital files
    because it's based on the photographic process of developing through a
    screen with a grid of holes... with a film transparency overlaid. The
    brighter areas burn each dot down to a smaller dot, the dark areas make
    bigger black dots. And it's measured in lpi (lines per inch) just to
    make things more confusing... halftones can also be done with lines
    where the line simply gets fatter or thinner according to the exposure.
    Digital is not good at achieving this because digital can only jump by
    full pixels and cannot make gradual size increments like film.
    Paul Furman, Sep 19, 2007
  6. Which I would say would be "samples per inch."
    Don Stauffer in Minnesota, Sep 19, 2007
  7. eugene

    dj_nme Guest

    How about "sensel pitch", usually stated in nanometres (nm)?
    I think it depends on the manufacturer, as this seems to be rarely
    described as a feature of a camera's sensor by most manuafacturers, some
    describe it also as a "pixel pitch", it's usually only described with an
    overall megapixel (mp) rating and it's inch-size (as in: 2/3") or crop
    factor (as in: 1.5x).
    dj_nme, Sep 19, 2007
  8. eugene

    jdear64 Guest

    I think you meant micrometers ( AKA microns ), 0.000001 meters.
    jdear64, Sep 19, 2007
  9. eugene

    Wayne Guest

    The first sentence above is correct, dpi can only mean pixels per inch there.
    The second is not correct, or at least is quite hasty and rather incomplete.

    There can only be one interpretation of dpi as concerning any image file, at
    least if from a scanner or a camera, any and all those images we have to work
    with. Both terms dpi or ppi are only about paper, because the only place
    inches exist is on the paper. Regarding images, all inches are on paper.
    Technically, the image file only has pixels.

    Certainly the term can never mean ink drops if about image files. There are
    no dithered ink drops in image files, which I think was your meaning. But we
    do print those image files to our printers too, at perhaps 300 dpi, meaning
    pixels per inch on paper. Then after inside the printer, there may be
    another definition that comes into play to create the ink drops to do that
    job of printing 300 pixels per inch on paper.

    This whole notion of sematics about dpi is really dumb. For example, my big
    dictionary has 116 definitions for the word "set". First one is to put
    something in a particular place, and the last one is stubborn or obstinate.

    The analogy is that some of us (I do not mean you Paul, I think your
    intentions were good, but I mean others in past days) are obstinate,
    insisting words can only have one meaning, specifically insisting the only
    possible valid definition is the one they are able to understand. And when
    newbies figure out there are two definitions, some of them go crazy inventing
    their own rules for the rest us to abide by. Which is nonsense, because in
    the real world, image resolution has always been called dpi (meaning pixels
    per inch), and always will be called dpi. Just a name, but that is simply
    the name that has always been used. So much easier to just accept that it is
    used, because it definitely is used.

    Saying PPI is fine too, no problem at all with ppi, that is indeed what it
    means, but we absolutely must understand it either way, ppi or dpi, because
    we absolutely will hear it both ways. It is very much like the word "set"
    too, we need to understand the usage context determines the meaning.

    I do not argue about which is "correct". Both are correct. Ppi may be more
    clear to newbies, use it if you wish, but the name of the term has always
    been dpi, and it is fully correct too. Always has been.

    I only argue that both terms are used with the same meaning.

    The point being that the only correct answer to such questions is that it is
    called both dpi and ppi, either one interchangeably. Pick one and use it
    yourself, but understanding that both are used is essential, or else we don't
    know much, and we will remain confused.
    Wayne, Sep 19, 2007
  10. For high-end printing (on a conventional press) the resolution was
    typically 300-400 dpi at the imagesetter. Exactly equivalent to 300-400
    pixels per inch in a TIFF file. My (Canon) 6-color inkjet printer
    produces a similar look from an image file whose resolution is as low
    as 144 ppi, and in fact higher res than that simply increases file size
    (slows down printing) w/o any increase in quality.

    YMMV. To test your own set-up, output images at 72, 144 and 300 ppi,
    with the highest quality settings and the best paper you intend to use.
    My iP6700D does a really nice job with International Paper products
    branded "National Geographic." I buy it when it's on sale at the same
    price as Epson papers. For uncoated I like Hammermill Great White.
    sheepdog 2007, Sep 19, 2007
  11. eugene

    just bob Guest

    No. Which program are you using? You should be able to change it to whatever
    they want without resizing.

    On second thought, maybe they did mean they wanted it 350 pixels wide,. Is
    it for web?
    just bob, Sep 19, 2007
  12. eugene

    dj_nme Guest

    It depends on who wrote the camera review article, they may use nm or
    um, depending on whether they wish the pixel/sensel pitch to look large
    or small.
    dj_nme, Sep 20, 2007
  13. eugene

    HEMI-Powered Guest

    sheepdog 2007 added these comments in the current discussion du
    jour ...
    I have a Canon Pixma 6600 which I find to produce superb images
    on all the glossy Canon papers I've tried. Since my primary
    subject is cars and other subjects that look "sharper" on glossy
    paper, I've not done very much with the semi-glass and matte
    papers other than just run a few tests.

    It's refreshing to hear that I am not the only one who is happy
    with relatively low PPI. I normally create my finished images at
    1400 x 1050, no larger than 1600 x 1200 unless I know in advance
    I will be printing for max quality. So, for a borderless 8.5 x 11
    print, the PPI is pretty dismal - under 130. Yes, or course I can
    see aliasing, especially on the near-horizontal or vertical
    character lines and chrome moldings on my cars. But, since I
    print so rarely and view from a distance where the aliasing is
    not bothersome to me (it would be clearly unacceptable to most
    people based on what I've read on this NG), I am happy as the
    proverbial clam.
    I already "rang in" with my views on the differences between
    "DPI" and "PPI", so please excuse my hyjacking this thread. I
    changed the subject so that no one would read my post thinking it
    was a continuation of the DPI/PPI debate.

    My question for you, sheepdog, is what exactly is "National
    Geographic" paper? I can see that you said it is manufactured by
    International Paper but I cannot recall seeing NG as a brand of
    their paper. Is it ultra-glossy, glossy, semi-gloss, matte, or
    what? Most importantly, how is the price/sheet compared to
    Canon's brand and how would you compare quality?

    When I am printing test prints or photos where I don't need the
    higher cost of glossy paper, I have also found Hammermill to be
    about the finest non-photo paper, although it is pricier than
    normal "copier" paper.

    One other question: Do you use the High or Standard print quality
    setting in the driver? Or, have you created your own custom
    settings? My 6600 just drinks ink like it was water, as do most
    high-quality photo printers, so I also tested both driver
    settings on the same paper with the same car. Besides the paper
    being wetter and the print time much higher, I could scarcely see
    any difference so I have gone to Normal as my "normal" (couldn't
    resist the pun!) setting. Besides, it seems to make no sense to
    waste so much expensive ink on a print coming from an image with
    only 1/2-2/3 the PPI that ordinarily be needed for a "good"

    Your comments would be appreciated, and again, I apologize to
    those who may be upset that I hyjacked this thread, it's just
    that so much of what you talk about I find to be equally true.

    Have a great day!
    HEMI-Powered, Sep 20, 2007
  14. eugene

    HEMI-Powered Guest

    just bob added these comments in the current discussion du jour
    I agree that DPI and PPI generally have two completely different
    meanings, but in the photo editors I've used, I can change the PPI
    (some actually do call it DPI) with or without resampling. Quite
    some time ago, when I was using Adobe PhotoShop 5 LE that came with
    my old Microtek scanner, changing the PPI was the only way to alter
    the print size.

    Since I do not use custom print shops, I've not run into the
    problem really being discussed here, but I do occasionally change
    the print size to something in inches that has meaning to me by
    first unchecking the "resample" box. One reason I do that is to
    save the picture in the correct aspect ratio for an 8 x 10 or 8.5 x
    11 but leave enough space for the narrower aspect ratio of a 4 x 6.
    Thus, it helps me to know how much to crop to get an image that
    will (almost) exactly fill the printed sheet.
    HEMI-Powered, Sep 20, 2007
  15. If you remember when RC photo paper first came out, there was a big
    discussion about 100 year archival prints. There was no usenet then,
    but if there had been, the thread would still be running today. Anyway,
    the glossy printer paper I use is resin-coated and without making wild
    claims, i just like the way the results`look. National Geographic has a
    page on their website promoting their own brand of photo and inkjet

    For matte coated paper I'm using Epson Matte Paper Heavyweight. I also
    like Epson's Premium Luster.
    Actually, The only time I print color on the uncoated stock is for
    thumbnail catalogs.
    I'm using high quality settings for everything except text. I have a
    profile called "mono" for pages which have no images, or only 72 px/in
    images; then there is the "color" profile which gives a dialogue box
    with menus for type of paper and purpose.
    When it comes to my printer's thirst for ink the adjective "awesome" is
    completely appropriate.
    sheepdog 2007, Sep 20, 2007
  16. eugene

    HEMI-Powered Guest

    sheepdog 2007 added these comments in the current discussion du
    jour ...

    I will take a look, thanks muchly for the link! I don't think I
    go back to the resin coated "wars". My first involvement with on-
    line anything was the old CompuServe. I think Usenet was there
    back then, circa 1990 or so, I just didn't know about it.

    In those days, my car picture collection hobby was very small,
    limited only to scanning from books and magazines or my own
    snapshots. I had a couple of HP ink jets back then, one of which
    is the wide-carriage 1220C that still works today. I don't know
    off-hand what technology of "paper" it uses. At one time, it
    wasn't paper at all, but some sort of plastic material that
    allowed ink to adhere to it.
    I take it from your comment above that you buy and use paper that
    you've tested to produce results that are pleasing to you rather
    than by manufacturer. I did the same thing for my HP 1220C, using
    Epson Super B 13" x 19". Worked just fine.
    Actually, for ordinary printing, Hammermill is a bit pricey for
    me, but I DO use it for test prints prior to a final on the more
    expensive Canon glossy because it gives a reasonably good
    approximation of color fidelity, brightness/contrast, and
    Again, I'm making some assumptions here. I take it that your
    tests show that the higher ink consumption and longer print times
    are justified by the results you desire. I can't argue with that!
    <grin> Whenever there's a discussion hereabouts about PPI or just
    about anything, what the photographer personally prefers, needs,
    or wants somehow gets lost in the theoretical discussions. It
    sounds to me like you're a pragmatist like I am, meaning that I
    make quality judgements based on some controlled testing rather
    than just independent lab testing or the opinions of others.

    Subject matter, lighting, camera/lens type, PPI, and a dozen
    other factors make firm assertions tough to support IMO. Seems to
    me that what the user likes is what they like. I try very hard to
    NOT tell other people what to do, although I do try to give them
    the benefit of my personal experience and let them make up their
    own minds.
    Yeah, I'd saw "awesome" is one adjectivive. Outrageous might be
    another at some $15/cartridge! One last question, I promise!: do
    you buy "genuine" Canon ink cartridges or do you get yours
    refilled someplace to save $$$.

    Thanks for your views on on of this. If my primary purpose was
    printing my images, I'd have a completely different printer and I
    certainly would create images with a much higher PPI number. Have
    a great day!
    HEMI-Powered, Sep 20, 2007
  17. Speaking as someone who can cross the line--w/o warning--to a
    blowhard/know-it-all/pedantic rant (sometimes I actually bore
    _myself_), I think we all write in strenuous prose if we feel strongly
    enough about a subject. Maybe the key is self-censorship. On this
    thread, I purposely avoided throwing lines/inch (lpi) into the mix. For
    anyone who wants to know, halftone screen rulings (more dinosaur
    technology) ran to 150-175-200 lpi in my day. The ratio of lpi to dpi
    was 1:2, i.e., to print 200 lpi separations (CMYK) you'd want to output
    400 dpi at the imagesetter. A 200 lpi screen laid down 200 halftone
    dots per linear inch on the press. Can you see how tempting it was to
    spew out all this in my initial answer? Since this is a whole different
    yardstick of dots per inch, I left it out for clarity.
    I don't like to waste money, but I tried refilled cartridges in the
    past, as well as bargain brands of new carts. I had problems that
    wasted too much of my time and mental energy. Some people enjoy
    applying their creativity to solving such problems, but my own
    preference is to find something that works for me and stick with it.
    That's not better than the next guy's solution, it's just what works
    for me.
    I scan at 300 px/in, the same way I capture images on the D80s. I
    archive as 300 px/in TIFFs, edit as 300-res PSDs,create JPEGs in 72-res
    for web and 144-res for the printer.
    sheepdog 2007, Sep 20, 2007
  18. eugene

    just bob Guest

    Right , I resize without resampling the same way: I usually print on 13x19"
    paper and change the dimensions to 12x8" so I get a half inch border.

    If I take a Canon 1DM3 file that is 3888 x 2592 pixels and Bridge with ACR
    converted the RAW file at 72 dpi, the Photoshop resize box says the
    dimensions are 54x36 inches at 72 "pixels per inch". When I uncheck Resample
    Image and change the dimensions to 12x8"", the pixels per inch changes to
    216. In this case 216 is my DPI.

    Now what has me confused is the new Getty photo service which sells a photo
    to anyone up to "72dpi up to 500KB" for $49. How can they specify dpi
    without specifying the dimensions? How/why can they make a general
    statement that it will be about 500KB? I can't see why they wouldn't just
    say, "you're file will be up 400 pixels max dimension and it's saved at JPEG
    quality 5", or something similar, which, IMO, seems like a better way to
    control the quality of the file you sell and it's how I've dealt with web
    just bob, Sep 20, 2007
  19. eugene

    just bob Guest

    Oh, one thing I wanted to add is I keep a default in the ACR raw converter
    to be set at 72dpi for all cameras because I have scripts which write
    various watermarks for different customers, and if one of the files is set
    to anything other than 72 the font sizes as specified in the actions will
    not come out right. That's really the only time I really about the DPI/PPI
    when processing for web.
    just bob, Sep 20, 2007
  20. eugene

    HEMI-Powered Guest

    sheepdog 2007 added these comments in the current discussion du
    jour ...
    In times past, I didn't want to risk screwing up an expensive
    printer using "cheap" ink, even though it may really be
    identical. These days are more like the time when Gillette used
    to literally give their razors away by using the logic that they
    could make their money selling blades. Still, I don't want to
    mess up a $200 printer that works just fine to save a few bucks
    on ink.

    I agree with your analysis on not wasting mental energy. While
    Canon ink may be pretty pricey, it is also of very high quality
    and ensures that prints will look good using their driver and,
    perhaps, their paper. In short, I have better things to do with
    my time than to try to figure out how to make my "inexpensive"
    ink produce the same quality as the Real McCoy.
    You lost me here, I'm afraid. When I am scanning, I set the DPI
    (correct usage of the term here) to produce the size image I want
    in pixels).

    I can't comment on your D80s as I have a Rebel XT, but I thought
    that the "scan" rate or whatever you want to call it, is fixed by
    the camera. When I bring my images into PSP 9, the PPI is set to
    200, not because that's what the camera produced but because that
    is PSP's default. I could just as easily change the default to
    1000 and the images would come in exactly the same size in

    I'm further confused by your last statement. Are you saying that
    you change the PPI/DPI to 72 for web and 144 for the printer or
    is your dimension "300 px/in" different than what I would call
    PPI (Pixels Per Inch).

    If you could, I'd appreciate a couple of sentences explaining
    what you mean here. Thanks and have a great day!
    HEMI-Powered, Sep 21, 2007
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