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People confuse PPI (pixels) and DPI (dots) all the time. Yes, a press might run at a higher DPI than 300, but a 300-400PPI image is generally considered suffici

People confuse PPI (pixels) and DPI (dots) all the time. Yes, a press might run at a higher DPI than 300, but a 300-400PPI image is generally considered sufficient for even coffee table book-quality printing. http://www.tildefrugal.net/photo/dpi.php http://www.tildefrugal.net/photo/dpi.php

jonah 16y ago
Aahh, you beat me to it. It's a common misunderstanding for many without experience in the print world.
bonaldi 16y ago
It's not quite as clear as that. People aren't confusing DPI and PPI -- they're the same thing. Pages like the linked that suggest otherwise are muddying the problem, because they're misunderstanding how printing works by ignoring line screening and halftoning. A 300ppi screen that fits 300 pixels into an inch is exactly the same as a 300dpi printer that can fit 300 dots of its laser into an inch of drum. The difference comes because screens can directly vary the colour of an individual dot. Printers can't -- ink is either present or it is not. The way you get around that is by varying the size of the dot, in a process called halftoning. Halftone dots are very small, and are arranged in patterns you'll recognise if you look at newsprint photographs close-up. You measure the size of the screen in LPI -- lines per inch, the number of lines of dots (at max size) that can fit in an inch. Because of the need to vary the size of the dots, on a 300dpi printer you end up with a very coarse line-screen of about 60 LPI. This looks rotten, and so printers go up to resolutions of 1200+dpi. This means you can have a linescreen of around 150lpi, which is good enough for most printing. Each line roughly equates to 2 pixels, and hence a 300ppi image is sufficient for printing, regardless of the resolution of the image or platesetter. But this doesn't mean there's a difference in ppi or dpi: they're still exactly the same.
- sesqu 16y ago
  If I understand this right, * DPI is print resolution, a property of prints and displays * PPI is image resolution, a property of printed and displayed images * LPI is halftone minimum printing resolution, a property of printers Those are absolutely not the same. DPI is looking at what you got; PPI is looking at what you wanted. LPI, then, is looking at what you can do, and each is measuring a different technological solution to "image". PPI is taking a digital image and saying "I want it yay big", LPI is saying "I'll do it by drawing at least this many differently sized dots of entirely different colors", and DPI is going "This is how many dots I'm counting you did it with". edit: Apparently, some manufacturers of small LED displays like to report DPI as the number of LEDs per inch - that is, 3x the native resolution for images. That's a good example for people like me, who know little about printers.
  - bonaldi 16y ago
    No, DPI and PPI are literally the same thing. (Photoshop used to call what is now PPI "DPI"). "PPI" comes from people wanting a way to talk about the dpi of a digital image without including all the baggage and confusion of dpi, which too few people understand. There's no technical difference, however.
    - sesqu 16y ago
      If they're the same thing, which thing is it? The number of pixels (virtual representations; samples) per inch of display, or the number of dots (physical representations; approximate components) per inch of display?
      - bonaldi 16y ago
        You've got a false distinction there. It's the number of constituents that can be packed in per inch: whether those constituents are print dots, physical pixels, or utterly notional (as in displayed images).
        sesqu 16y ago
        No, that's just the per inch part. I still need to know what the constituents being measured are, as logical pixel vs. physical dot makes all the difference: I don't care about the dot density, as long as there are enough of them; I care about the dots/pixel, and deeply about the actual inches. I ran into this problem as a kid, printing some images that had dpi metadata that the printer took literally, but I didn't know how to fix it back then so I ended up with a thumbnail print. Attaching ppi (!) metadata to images is stupid anyway, since the actually relevant information would be the inches (or the dots/inches, for designer decrees).
        deleted 16y ago
        [deleted]
        bonaldi 16y ago

jonah 16y ago

Aahh, you beat me to it. It's a common misunderstanding for many without experience in the print world.

bonaldi 16y ago

It's not quite as clear as that. People aren't confusing DPI and PPI -- they're the same thing. Pages like the linked that suggest otherwise are muddying the problem, because they're misunderstanding how printing works by ignoring line screening and halftoning. A 300ppi screen that fits 300 pixels into an inch is exactly the same as a 300dpi printer that can fit 300 dots of its laser into an inch of drum. The difference comes because screens can directly vary the colour of an individual dot. Printers can't -- ink is either present or it is not. The way you get around that is by varying the size of the dot, in a process called halftoning. Halftone dots are very small, and are arranged in patterns you'll recognise if you look at newsprint photographs close-up. You measure the size of the screen in LPI -- lines per inch, the number of lines of dots (at max size) that can fit in an inch. Because of the need to vary the size of the dots, on a 300dpi printer you end up with a very coarse line-screen of about 60 LPI. This looks rotten, and so printers go up to resolutions of 1200+dpi. This means you can have a linescreen of around 150lpi, which is good enough for most printing. Each line roughly equates to 2 pixels, and hence a 300ppi image is sufficient for printing, regardless of the resolution of the image or platesetter. But this doesn't mean there's a difference in ppi or dpi: they're still exactly the same.

sesqu 16y ago
If I understand this right, * DPI is print resolution, a property of prints and displays * PPI is image resolution, a property of printed and displayed images * LPI is halftone minimum printing resolution, a property of printers Those are absolutely not the same. DPI is looking at what you got; PPI is looking at what you wanted. LPI, then, is looking at what you can do, and each is measuring a different technological solution to "image". PPI is taking a digital image and saying "I want it yay big", LPI is saying "I'll do it by drawing at least this many differently sized dots of entirely different colors", and DPI is going "This is how many dots I'm counting you did it with". edit: Apparently, some manufacturers of small LED displays like to report DPI as the number of LEDs per inch - that is, 3x the native resolution for images. That's a good example for people like me, who know little about printers.
- bonaldi 16y ago
  No, DPI and PPI are literally the same thing. (Photoshop used to call what is now PPI "DPI"). "PPI" comes from people wanting a way to talk about the dpi of a digital image without including all the baggage and confusion of dpi, which too few people understand. There's no technical difference, however.
  - sesqu 16y ago
    If they're the same thing, which thing is it? The number of pixels (virtual representations; samples) per inch of display, or the number of dots (physical representations; approximate components) per inch of display?
    - bonaldi 16y ago
      You've got a false distinction there. It's the number of constituents that can be packed in per inch: whether those constituents are print dots, physical pixels, or utterly notional (as in displayed images).
      - sesqu 16y ago
        No, that's just the per inch part. I still need to know what the constituents being measured are, as logical pixel vs. physical dot makes all the difference: I don't care about the dot density, as long as there are enough of them; I care about the dots/pixel, and deeply about the actual inches. I ran into this problem as a kid, printing some images that had dpi metadata that the printer took literally, but I didn't know how to fix it back then so I ended up with a thumbnail print. Attaching ppi (!) metadata to images is stupid anyway, since the actually relevant information would be the inches (or the dots/inches, for designer decrees).
        deleted 16y ago
        [deleted]
        bonaldi 16y ago