OS X Quartz vs. Windows ClearType

Published by marco on

The release of Safari for Windows seems to be the only issue worth discussing for most of the technology world. Whether it’s the horrific zero-day exploits (already patched, but still a rocky start), the crashing bookmarks for non-US English-speaking users or the ridiculous amount of effort put into making Safari exactly the same on Windows as it is on OS X—including all controls (scrollbars, buttons, etc.), behavior (can only resize from the bottom-left) and, last but not least, the alternate sub-pixel rendering model used by OS X to render text.

It is this last point that is especially interesting because, unlike Apple’s decision to replicate their chrome—which people unanimously agree is highly hypocritical considering the scorn they heap on applications that don’t conform to their own HIG—there are good number of people who claim to prefer Apple’s rendering model.

Windows users, accustomed to either Cleartype or no sub-pixel rendering at all (a jaggy useless mess for anyone serious about text presentation), almost unanimously derided the Safari rendering as “blurry”. Granted, it is blurrier than ClearType, which is most vexing on the UI elements. Larger swathes of text—like a page of text—tend to look much truer to the printed version and almost photorealistic, as opposed to Cleartype, which tends to be almost “too sharp and blocky”. Font smoothing, anti-aliasing, and sub-pixel rendering by Joel Spolsky (Joel on Software) has the following astute description of the differences between the algorithms:

 Windows vs. OS X font rendering

“The nice thing about the Apple algorithm is that you can lay out a page of text for print, and on screen, you get a nice approximation of the finished product. This is especially significant when you consider how dark a block of text looks. Microsoft’s mechanism of hammering fonts into pixels means that they don’t really mind using thinner lines to eliminate blurry edges, even though this makes the entire paragraph lighter than it would be in print. … The advantage of Microsoft’s method is that it works better for on-screen reading. Microsoft pragmatically decided that the design of the typeface is not so holy, and that sharp on-screen text that’s comfortable to read is more important than the typeface designer’s idea of how light or dark an entire block of text should feel. (emphasis added)”

The emphasized line above was also cited by A subpixel Safari by Dave Shea on June 12, 2007 (Mezzoblue), who pointed out that it smacks of an attitude of “programmers knowing better than experts in their respective fields”, which ends up “marginalizing type designers”. The difference between the rendering technologies is only blatantly evident when seen side-by-side; the brain acclimates to each one on its own relatively quickly. This basic difference between the two operating systems is probably the single biggest reason that so many people use OS X for graphics design: What You See really Is What You Get. As pointed out by many, applying that same technique to elements that will never see a printed page is overkill, especially when it means that menu items and control labels are not lined up on the pixel grid and look blurry. This might seem like a killer problem for Apple, until you consider the following:

“Here’s the caveat though — high resolution displays. At 100dpi, ClearType wins out, but we’re not going to be stuck here much longer. Give it a few years, let’s do this comparison again when 200dpi is standard. I suspect the pixel grid won’t matter nearly so much then.”

In effect, ClearType is like the game engines of yore (like Quake II or Quake 3): it contains optimizations that let it perform optimally on the hardware of today. However, these optimizations aren’t going to scale well at all on newer hardware, since the rendering anamolies caused by “hammering fonts into pixels” will never go away. Apple’s algorithm, on the other hand, is like the newer engines (like Doom or Unreal 3): it’s truer algorithms makes it look blurry in comparison (as Doom 3's truer rendering made it run more slowly than other engines), but it is far better positioned to improve automatically as hardware improves.

This is not the first time that Apple has chosen investment in long-term vision versus short-term pragmatism—the initial OS X was a poor fit for the machines of the day. A few years—and many software and hardware improvements—later and most people can barely remember when OS X was considered slow or RAM-hungry. Similarly, id’s Doom engine used to run well only on the newest graphics cards, but games based on the technology are still being developed today and the technology has scaled incredibly well—even when compared to much more recently developed technology. Cleartype is very readable on-screen, but takes liberties with text representation, whereas Apple’s sub-pixel rendering is the hands-down winner for faithful font representation, but takes some getting used to on screen—for now. In a few years, Apple’s rendering will start to look better to a lot more people. With the iPhone screen weighing in a 160 pixels per inch, that’s probably the first place their investment will pay off handsomely.