Did Mac OS recently switch from 72 DPI to 96 DPI?

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Level 1

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Did Mac OS recently switch from 72 DPI to 96 DPI?

I ask this because my MacBook renders text at 96 DPI, whereas I read everywhere that Mac OS (X?) renders text at 72 DPI, and MS Windows renders text at 96 dpi.

Note I'm only talking font points to pixels, not pixels to screen (which is dependent on the display).

For example, on TextEdit in plain text mode a 16 point font is rendered at 21 pixels, and that corresponds to 96 DPI (if it was rendered at 72 DPI, it would be 16 pixels instead of 21).

I had a look at the "System Profiler" > Graphics/Display, but I couldn't find a DPI value. It only mentions resolution (e.g. 1366x768).

So, do you know if Mac OS recently switched from 72 DPI to 96 DPI? And if yes, do you know at which version it made the switch?

MacBook Air, Mac OS X (10.6.8)

Posted on Jul 7, 2013 3:34 AM

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Answer 1

Top-ranking reply

Kurt Lang

Level 9

62,298 points

Jul 7, 2013 12:29 PM in response to Stefano_T

I don't believe that old standard applies anymore. At least not with Apple. Long ago, it was easy to build a consistent DPI into the OS since CRT monitors were pretty much either 640x480, 800x600, or 1024x768. We're way past that now with higher pixel counts per inch, and widely varying native monitor resolutions.

From what I have been able to find, you can use a formula to figure out what the DPI (PPI) is for your monitor. To do that, you need to know the dot pitch of your monitor (the distance between each RGB triad) and the monitor's resolution. As an example, a monitor with a dot pitch of 0.250 mm computes to 101.6 DPI. So if that monitor has a horizontal width (not diagonal) of 29.7", then the actual DPI is 101.6456. (Stolen from Malcolm Rayfield's post). Photoshop User Group magazine also posted a formula for this, but I couldn't locate that one.

This article explains how Microsoft tried to come up with a fixed formula that works with all monitor sizes. Good idea, but didn't work if the monitor itself computed everything to 72 DPI. Then everything Windows displayed would be ⅓ too big. This is an excellent example of how difficult this issue is. Note that the native DPI for the listed devices are all over the place.

Apple is trying to come up with a design for monitor resolution independence. Here's some of the details on how it's supposed to work. But basically, a fixed OS DPI that works doesn't exist. At least not yet.

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Answer 2

Stefano_T Author

Level 1

17 points

Jul 9, 2013 4:04 PM in response to Kurt Lang

Thanks Kurt, but this was not the info I was looking for.

My point is, how comes my Mac is behaving as a 96 dpi OS, where this is not documented anywhere that I know of?

In fact, as I said, I've found plenty of documentation saying the mac is a 72 DPI OS

(for example, wikipedia) and, even after extensive googling, I have found none saying it is a 96 DPI OS?

In fact, everywhere it says Windows is a 96 dpi OS, and I've verified that.

Every rendering engine has a specific DPI count, which does NOT relate to the question "how many pixels (or points) do I need to specify if I want my text to be x inches tall" (by the way, I call that "pixel-to-screen" resolution, or "points-to-screen" resolution). That depends on the screen.

The DPI I'm talking about answers the question "how many points do I need to specify if I want my text to be x pixels tall". I call that the "points-to-pixel" resolution. That doesn't depend on the screen, it only depends on the OS (at least, when there's no "software" zoom, that's why I take TextEdit as a test on Mac, and Notepad on Windows).

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Answer 3

Kurt Lang

Level 9

62,298 points

Jul 9, 2013 7:11 PM in response to Stefano_T

The DPI I'm talking about answers the question "how many points do I need to specify if I want my text to be x pixels tall". I call that the "points-to-pixel" resolution. That doesn't depend on the screen, it only depends on the OS

Windows does indeed have a setting where you can specify the DPI it uses, with a default of 96. Like you, I could find no reference other than 72 for the Mac OS. Any other attempt at DPI, PPI, resolution, or other terms always just turned up references for monitor resolution. Not what you want, or what I was looking for, either.

But you're still pretty much stuck. This has been a very loooooong time issue on the Mac OS. Couldn't tell you if Windows is really any better. I can go into just about any app on my Mac and have it display what that app says is 100%, or print size and get all kinds of interpretations. Quark is different than InDesign; InDesign is different than Photoshop. TextEdit is again its own thing. On and on. There's no consistency.

To see something really weird and without any sense whatsoever, place any text into TextEdit as plain text and print it. Now simply change the size of the TextEdit window and print it again. Even though it's "plain text", the size of the output changes with the size of the edit window.

Edit: Aha! Looking with the correct phrase, "os x dpi", I get lots of hits. As expected, the general answer is no, the Mac OS still does not have a global DPI setting. It's all application independent. Each app does whatever it does and is unlikely to be the same as another app. So trying to find a magic point size that will always be xxx pixels tall would be a lesson in frustration.

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