I thought maybe the most interesting single thing about the new iPhone 4 was its display, not so much the 960 vertical dots but the 326DPI, in the cleverly-named Retina Display. Which leads me to wonder, how much does this matter?

300 · If you care about this subject, I recommend a quick trip to Wikipedia’s List of displays by pixel density. In the keynote, Steve claimed that there was some sort of a threshold around 300DPI having to do with the resolving capabilities of the human retina (thus the name).

Indeed, three hundred is an interesting number; the first wave of personal-computer printers which produced results that actually looked really good started at 300DPI. Right now, per Wikipedia, there are exactly three devices in the world whose displays exceed it; along with the iPhone, the Toshiba G900 and the Sony/Ericsson Experia X1, both WinMo phones.

Also I can testify that my Nexus One, at 250DPI or so, is astoundingly sharp; the first thing in years that’s made me want to tune up the typography on my blog.

Take Me Higher · At the same time, I’m not sure about the importance of that 300DPI elbow. It’s sure not there on paper; today’s commercial laser printers commonly run at 1200 or 2400DPI. And high-end commercial pre-press products go way higher; the devices in the Heidelberg Prosetter family range up to 3386DPI.

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.

Do We Even Need It? · I hope so, because I sure love the look of these things, but I’m not 100% convinced. I’m typing this on a generic Dell 30" 2560x1600 display offering a pathetic 101DPI, and for the stuff I do all day, it makes me very happy; I’d have a hard time sacrificing any of that real-estate (4,096,000 pixels!) for higher density.

For serious photo-work I use a 25" NEC 2690 that I bought because it was good enough for James Duncan Davidson, and everything looks immensely better there than it does on the big Dell or my 113DPI MacBook, but that’s not because of the 98DPI, it’s because of the wonderful color.

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.

Some other relatively low-res devices that seem beautiful to me: the iPad at 132DPI, and my nice 42" 1080p TV at home, at a laughable 52DPI.

I gotta say though that those high densities are a joyful experience on hand-held devices; is it as simple as the fact that you hold them closer to your face? Is there a placebo effect at work?

Economics · Do bear in mind that all these extra dots are not free. I’m fairly ignorant about the manufacturing trade-offs, i.e. how much extra it’s costing Apple to put 614,400 dots on the iPhone 4, as opposed to the the 3GS’s 153,600.

I tend to worry more about the software costs; you have to manipulate 4 times as many pixels every time you double the DPI, and while we’ve learned a lot of tricks over the years, and increasingly push the work down into display controllers, the computing cost is very far from zero.

Typography · Anyhow, the best way to make a good looking page on the screen, particularly now that browsers are getting smarter and more polished with their font-handling, is with good typography.


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From: Michael Kozakewich (Jun 07 2010, at 14:29)

Apparently, the limit of the eye is a bit less than 600 DPI. I suspect the limit of 300 DPI has something in common with JPEGs and the 128 Kbps MP3s -- they're acceptable.

I can barely stand 100ppi monitors, because I can see every single individual pixel. I was working with a 3x5 pixel font for the past year (Shaun Inman would be proud), but I could still read it easily.

Actually, back to the MP3 analogy: it's been like listening to 42kbps music every time I use a computer. I'm so glad this is getting a lot of press, so it'll suddenly become a 'big thing' and get more implementation.

Though I agree, 300ppi is enough; don't want to ruin our resources.

(I'm stoked at the idea of a 12" monitor at 1920x1200.)


From: MIchael (Jun 07 2010, at 14:32)

52 DPI is fine when you're not 12 inches away from the display. Dots per radian might be a more relevant measurement, but it's user-dependent. Compare the 300 dpi handhelds at 9-18 inches from the eye (for the non-presbyoptic youth, at least) to a laptop at 2-4 feet to a television at 5-10 feet.


From: Michael Thorne (Jun 07 2010, at 14:51)

"Is there a placebo effect at work?"

Somewhat - being a photographer I'm sure you are aware of the "Circle of Confusion" - http://en.wikipedia.org/wiki/Circle_of_confusion - the same holds true for the human eye.

It is generally accepted that a normal human eye can distinguish 5 lines per millimeter at a distance of 25 cm. - http://www.nikonlinks.com/unklbil/dof.htm

So, 5 ln/mm x 25.4 mm/in = 127 ln/in, double this for fidelity, like we do for digital audio, to get 254 ln/in and anything over this is a bit of over kill as most people will not be able to see the difference.


From: Tony Finch (Jun 07 2010, at 15:25)

One key difference between print and pixel is that one is binary and the other is analogue. A 1200 dpi printer can produce 16 levels of each primary colour in the space of a 300 dpi pixel, whereas a colour screen can produce at least 64.


From: Mark Nottingham (Jun 07 2010, at 15:38)

One reason modern printers have much higher resolutions so they can support finer halftones; a 300dpi printer can only print a very coarse halftone screen.

If you need that sort of thing; phones usually don't.


From: Jason (Jun 07 2010, at 16:15)

The very high resolution of printers is at least partly due to the use of dithering for color and greys. Dye-sublimation printers, which use less (or no) dithering for color are often in the 300-600dpi range.


From: g (Jun 07 2010, at 17:06)

I'm not sure how good the comparison between printers and computer screens is. The quoted DPI figure for a printer will be the resolution at which it can produce dots, but typically there won't be very fine control over the size or colour of those dots. (For those 300dpi laser printers, none at all: each pixel is either black or white.) Every pixel on an LCD display, on the other hand, will have maybe 18 bits (6 each for R,G,B) to play with.

So for black-and-white content, the effective resolution of the LCD will be higher than its nominal DPI because of antialiasing; for content with smoothly varying colours, the effective resolution of the printer will be lower than its nominal DPI because of halftoning.


From: David Magda (Jun 07 2010, at 17:54)

@Michael Thorne

> double this for fidelity, like we do for digital audio

Humans can (theoretically) hear up to 20 kHz, and so we record music at greater than 40 kHz (double) not for fidelity, but because of mathematical necessity. See Nyquist frequency:


So if humans can see roughly 127 ln/in, that sampling math may also be necessary for the doubling of resolution up to 300 for the same reason.

I've not studied optics, so I don't know if any of this is actually true though.


From: anonymous clod (Jun 07 2010, at 18:01)

Re: What DPI is the maximum needed?

Short Answer:

This depends on three things:

1)The DPI of the screen

2)How far the screen is from your eye 3)The resolving power of your eye. (see Long answer)

3 varies quite a bit from person to person. 300DPI may be at the limit one person can see if he holds it at arm-length, while another person might not be able to distinguish 200DPI from 300DPI if the screen is right in front of his nose.

If you want to play around with this yourself, just display some patterns involving 1 pixel-wide lines on your iPhone and then move away from it until it just barely blurs into a mess. Then try that with another display with a different DPI. You should wind up standing different distances from the device.

Long Answer:

If you want to know what DPI really makes a difference, what you really need to know is the resolving power of your eyes.

Images you see are formed by light passing through your iris and hitting different photoreceptors (i.e. rods and cones) on your retina. The angle at which the light hits your iris determines where it falls on your retina. It's fairly easy to see that the size and spacing of photoreceptors in your eye place a limit on how close two light ray angles can be before you can't distinguish them. Your eyes are not perfect optical instruments, so other optical aberrations also contribute to make things a little worse than this.

Once you know the resolving power of your eyes you can calculate how far two pixels of a given size need to be from your eye to be just barely resolvable as two pixels, and not one blur.


From: Greg Pfister (Jun 07 2010, at 18:02)

Let's not forget the other direction, too -- scanning. Scanning at 300 dpi, which seems to be a usual default, produces images of text that just don't read well. I have to go to 600 dpi and greyscale to get something usable.

I suspect the 300 dpi case is used just because it's faster; 600 dpi on my scanner (HP 5600 all-in-one) is a lot slower. But for me, it's more than worth the wait.


From: Andy Anderson (Jun 07 2010, at 18:25)

Most people, if they compare 300 dpi with 1200 dpi print, will be able to observe that the latter is crisper. But they might not care that much.

But if they compare 100 dpi with 300 dpi print, they will notice and really appreciate the difference.

Conclusion: calling this a "retinal display" is hype; nevertheless the difference will certainly get people's attention.

I predict that in a few years this will be the standard for smart phones. But it will take much longer for larger screens due to the high cost of production (if I remember correctly, the LCD yield decreases with larger size). But I look forward to it!


From: Pavel Zaitsev (Jun 07 2010, at 22:27)

Usual printers DITHER dots to show color and/or greytones. The more DPI you have the smoother the result will be.

If you have some ink offset ( or some such name ) technology printer. 300dpi is just fine. For displays 300dpi is excellent too as they are very good at displaying intensity and variations of color in a very small space.

Therefore dpi on screen and printer for what they are marketed aren't related in way their usefulness is perceived.


From: Jonas B. (Jun 08 2010, at 01:02)

The comparison with laser printers is not really fair. Since after their DPI wandered off into fantasy world (that is, over 300 dpi) they tend to be less meaningful.

The individual dots are much larger than 1/1200" on 1200 dpi printer so there is a large overlap. And when you measure precision but give no deviation limits there is a lot of trickery possible.

The result is that printer manufacturers basically dream up these numbers themselves.


From: Julian (Jun 08 2010, at 01:05)

Printer dots and display dots are completely different. A printer dot is a drop of ink, with perhaps a small number of variations in volume (e.g. 4). A screen dot is three pixels (RGB) which can each have 256 levels of brightness. That gives a screen dot 16m possible colour values. For a printer to produce that many values, a number of physical ink (or toner) dots need to be used together.


From: Gavin B (Jun 08 2010, at 02:08)

anonymous clod said it well but I can add a couple of points

(1) Foveal/peripheral vision.

- bear in mind when you look at you tiny screen it usually occupies the area of visual field that projects onto your fovea or neo-fovea, and so while you are perceptually wired to read and see crisp color you get disadvantage by your peripheral vision that alerts you out of the screen - this happens much less on large screens.

(2) Vernier acuity -see



foveal vision can notice tiny misalignment of things at sub retinal-resolution. So your mileage may vary!


From: g (Jun 08 2010, at 03:08)

Lots of people (including me) saying the same thing here, on account of moderation delays.

Suggestion #1: display the number of comments waiting for moderation. (If I'd seen "3 comments waiting for moderation" I wouldn't have bothered posting what I knew was a fairly commonplace observation.)

Dunno whether that would fit naturally into your mostly-static blog workflow, though. (I have what I suspect is a similar setup, and it wouldn't fit well into mine.)

Suggestion #2: display posting times as well as submission times for comments. Display them lighter, so that they're easy to ignore.


From: Daniel (Jun 08 2010, at 08:25)

That there is so much cackling about this topic in this blog post once again proves that Apple has raised the bar and is whaling upon Android! Its great to see such competition. Let's see Android try to whale on Apple now. Its like watching gladiators in a ring (and the funny part is all the geeks on the sidelines who, all they can really do, is contribute opinion which is like noise, like noise in a stadium with lots of people watching the fight but the the noisy geeks are not on the playing field because they don't define the playing field)!


From: Jon (Jun 08 2010, at 08:59)

Printing is a completely different beast than a screen.

(correct me if im wrong or my description doesn't work)

In [offset]printing, you have either an on or off with either 0 or 100% "brightness", ie. theres either a dot or there isn't. Having a higher resolution correlates to how well you can reproduce something, as you have finer control over "white space". This goes for 1 color or 8 - look at sample gradients printed at 150, 300, 600, 1200 dpi - you perceive more grey levels the higher the DPI.

On a screen, pixels have luminance, or the levels between on and off. Besides that one is transmissive and one is reflective, you also have the issue that even at high resolutions out of the imagesetter (or whatever the equivalent is now), most images are sent tot he printer at between 240 and 300dpi - except for some extreme circumstances, printers still throw away a lot of that image data. (even on a high end desktop inkjet).

High pixel densities right now are terrible on the desktop, since no major OS supports a true resolution independent UI - ie, keeping objects the same relative size despite containing 4x the image data.

As for phones, and ipad like devices, it's great - small devices gain the clarity of print - because they dont need "white space" to create different levels of grey/color, the finer grain of the sub-pixels (the bits of grey that create the illusion of a round edge) creates a far sharper image, which in turn is way more pleasing to the eye.


From: /b (Jun 08 2010, at 10:27)

I'm guessing the Droid is part of the reason they did this. The first thing everyone I know says when they look at one is "wow, what a pretty screen."


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