Dots Per Inch

http://www.tbray.org/ongoing/When/201x/2010/06/07/DPI

by bootload • 16 years ago

36 31 16 years ago

yish• 16 years ago

DPI is a pointless term in comparing different medium. One of the comments mentions Dots per Radian of viewing angle which I think makes much more sense. Don't need/want my TV to have 300DPI, but 30 DPI would actually be pretty awesome there.

Yaggo• 16 years ago

Indeed. Any medium (regardless of dot size) will appear razor sharp when viewed from far enough (so that one can't see individual dots).

Of course, if there are enough dots in particular physical area, the human eye is incapable to see a single dot from the closest possible focusing distance. This is what I would call a "retinal diplay". Not sure if 326 DPI is enough for that, but is surely enough for the iPhone's screen.

http://en.wikipedia.org/wiki/Optimum_HDTV_viewing_distance

sesqu7• 16 years ago

W3C recommends the pixel to be interpreted as about 4E-4 radians[1]. Personally I think that's a stupid idea, and I don't think anyone has implemented it, but I would support using such a measure for device resolutions.

[1] http://www.w3.org/TR/2008/REC-CSS2-20080411/syndata.html#len...

czhiddy• 16 years ago

> Given the nature of the Android ecosystem, I think we can be pretty sure that if it turns out that Apple bet right and the extra resolution is a good selling point, we’ll be in an amusing arms race around DPI PDQ.

Once you surpass the limits of human vision, where individual pixels can't be resolved at 12-24" distances (whether this is 300dpi or 400dpi, or whatever), there simply is no benefit to going higher. There are significant costs to increasing DPI, such as memory + GPU bandwidth. The hardware/manufacturing limitations are probably costly as well (does _anyone_ manufacture displays in volume with > 350 dpi?)

abeppu• 16 years ago

Just to be explicit about it, 20/20 vision corresponds to visual acuity that can distinguish features subtending 1 minute of arc. The angle subtended by a pixel at 326 ppi is arcsine( (1 inch /326) / 12 inches) = 0.87 minutes. http://en.wikipedia.org/wiki/Snellen_chart#.2220.2F20.22_.28...

But I think the psychophysics get more complicated when you throw in time and movement.

Derbasti• 16 years ago

I think that Apple is following Android here instead of the other way around. Still, I like the idea of having more pixels at my disposal. We will see what the app store will make of that.

feverishaaron• 16 years ago

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

jonah2• 16 years ago

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

marbletiles5• 16 years 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.

sesqu7• 16 years 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.

jonah2• 16 years ago

DPI [Dots Per Inch] != PPI [Pixels Per Inch] - this is a common misunderstanding when discussing screen resolution and they're not directly comparable.

DPI has to do with the printed image - how many of the smallest dots of ink can fit along an inch on paper. The resolvable image detail depends on this as well as other factors like the dithering algorithm.

PPI defines how many groups of pixels (each normally made up of an R, G, and B sub-pixel) fit in a linear inch. Even this is complicated by things like some of the current OLED screens that have twice the number of green sub-pixels than red and blue.

More: http://www.google.com/search?q=dpi+vs+ppi

tspiteri• 16 years ago

As stated in the article, laser printers do have much higher resolutions. But then ink dots are either there or not, you cannot have as many different colors as you can in one screen pixel. So comparing laser printer resolution to screen resolution is not so simple.

Also, it would be interesting to know at which point, as screen resolutions get higher, font smoothing becomes pointless.

ugh• 16 years ago

But then ink dots are either there or not, you cannot have as many different colors as you can in one screen pixel. So comparing laser printer resolution to screen resolution is not so simple.

A 300 ppi screen is a 1200 sub-ppi screen. Those subpixels are not as versatile as ink dots in some ways (a green subpixel can’t suddenly turn red) but more versatile in other ways (as you already said, a ink dot is either there or not – it can have a few different sizes but it’s arguably easier for a subpixel to change its brightness).

staunch• 16 years ago

My laptop (Dell D830) is 1920x1200 in 15.4": 147 PPI. I love it. I'd buy 2560x1600 at 15.4" if I could.

KirinDave• 16 years ago

I'm not sure what logical fallacy I'm committing (perhaps genetic fallacy?), but whenever Tim Bray talks about photography, images, typography, or really anything involving visual appeal I close the window.

Look at his blog. Look at his photography. Look at his outputs. He is a competent writer with technical knowledge , but when he starts making aesthetic arguments I think he's out of his depth. Especially when he uses other people's informed decisions to justify his uninformed ones (e.g., JDD's choice of monitor being good enough for him).

That'd be fine if this article was a researched technical argument, but it's not. This article is a "120ish seeems good enough for me, and I got this stuff from JDD and I seem to remember old printers being good at..."

jacobolus2• 16 years ago

Seriously. Where does he come up with nonsense like:

> I suspect that unless you’re preparing high-quality print work, there’s no appreciable benefit for a photographer, and perhaps some downside, in an ultra-high-res display.

Count me among (amateur) photographers who would just love to have a 300 DPI display on which to work on photographs.

Here for example is one quite obvious appreciable benefit: I can see at full resolution what my prints will look like with varying amounts of sharpening applied, in a roughly accurate simulation. Previously, if I opened an image up at 100%, the proper amount of sharpening for print would make an image look extremely “crunchy” on screen, because 100% on screen has pixels three times as big as a 300 PPI print resolution. If instead I looked at the image scaled to 50% on a typical display, I could no longer notice any difference from fine-resolution sharpening, because the screen display would be interpolated.

More than that though, I’d love to have a 300 DPI tablet-scale device to show off work on. Photographs would be absolutely gorgeous.

sesqu7• 16 years ago

So your argument is that 300 PPI displays are great for processing photos you intend to have printed at 300 DPI. I have no problem with this claim, and I'll extrapolate to "better for >= 300 DPI prints".

So, I guess the obvious question is, how much DPI do various prints come out with? And since almost all electronic displays have far less than 300 PPI, would you agree that web designers do themselves a disservice if they get a high-resolution display?

davidmathers• 16 years ago

my nice 42" 1080P TV at home, at a laughable 52DPI

Yes, it would be laughable if it was 6 inches from your face during normal usage.

houseabsolute• 16 years ago

Interesting that you should mention the typography of your blog because I always have trouble reading it and have been wondering for some time what about it makes it so hard.

mcav• 16 years ago

Line spacing (particularly between paragraphs) doesnt match, and header negative-margins make it look uneven to me.

jrockway• 16 years ago

Interestingly, according to the Wikipedia page, the OpenMoko phones had some of the highest-res displays, and they are already many years old. (I got one to play with, and the display was pretty nice. But the radios were crap, which kind of made it useless as a phone.)

ZeroGravitas• 16 years ago

I'm always amused at people advertising advances in technology, via the medium of the old technology.

So recent examples have been seeing adverts in Standard Def for High Definition devices or services. It seems to involve lots of slow-mo and highly intricate images that by their very existence on your SD screen mean you don't need an HD screen to view them.

Similarly DAB digital radio was advertised on standard FM radio with lots of space-age swooshy noises.

For high-dpi screens it seems water droplets are all the rage.

Dots Per Inch

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