MS's ClearType KOs Apple's Quartz In The Lightweight Division
Everyone seems to believe that Apple's Quartz rendering engine produces the best screen display. Unfortunately, I don't think that's indisputably so. Recently, I installed Windows XP under Virtual PC, and I found there's something interesting going on. Although Quartz rasterizations are superior in every other way (i.e., font spacing, kerning, etc.), however, text in XP, even under emulation, looks a bit clearer at smaller sizes than text under OS X. Then I double-checked by placing my PowerBook next to my PC's LCD display to much the same effect. This is impressive considering Quartz employs Display PDF for rendering. Windows XP uses ClearType technology. These technologies provide partial pixel rasterization, i.e., on LCDs and CRTs each atomic pixel is actually made up of red, green and blue sub-pixels. ClearType manipulates the intensity of such sub-pixels in effect to roughly triple the available resolution of a display. Quartz and Adobe Acrobat both do something similar, but with lesser results at smaller font sizes (at least on my PowerBook).
Apple's and oranges, but on Apples
For comparison's sake, I took a screen shot of my Mac OS X screen, above, with Windows having the exact same sample text at roughly the same sizes (if anything I zoomed the test document (to 137%) to produce slightly larger text under Quartz, thus, giving it the advantage of more pixels and raster area in which to work). The Tahoma font was taken from Windows XP and placed in my OS X font directory, while Times New Roman and Arial fonts are native to each OS. I took the screen grab with OS X font smoothing set to "medium," which was not significantly improved under other System Preference panel settings.
In a larger, pixel-for-pixel accurate screengrab, above, you might be able see that text under ClearType looks markedly clearer. If you're using an LCD (or a CRT with properly aligned sub-pixels) the difference should be relatively striking. Even if you don't have an appropriate monitor, odds are you'll still notice a slightly more fine-tuned rasterization provided by Microsoft's ClearType.
Now of course, perceptions of text rastering are highly subjective and depend on several factors, not the least of which are the quality of your sight and monitor and the distance you sit from your display. It also may depend on your preference for seeing details over your aversion to seeing pixelization. For example, at about 6" from your display, assuming you're not far sighted, you should easily be able to see the pixelization, i.e., the jaggies with globs of techno-colored grays, in the above XP or OS X samples of text. At about 12" from the screen, you should see a mixed bag.
The Nitty Gritty
In some spots, more pixelization is visible under ClearType. For example, the Times New Roman 12 Point "S" in "JUMPS" [See Figure 2 below] is a bit more pixelated under ClearType, but at least you can see the serif [Editor's Note: The linked page works in IE, Camino, or Mozilla, but not in Safari], which seems blurred out of existence under Quartz [See Figure 1 below]. However the "W"s and "Z"s seem more pixelated under Quartz [See Figure 3 below] than ClearType [See Figure 4 below]. This gets worse with smaller type fonts. The Times New Roman 8 Point "O" in "OVER" (reminding me of a song, but I digress) just disintegrates into a smoky ring under Quartz [See Figure 5 below], while under ClearType it stays sharp [See Figure 6 below], but slightly more pixelated. At about 20" to 24" inches from the display, which is my average reading distance, I don't really see significant pixelization under either Quartz or ClearType. However, when I compare Quartz and ClearType text at that distance, the ClearType is far more legible. When alternating my glance back and forth between the Quartz and ClearType samples (try it yourself in the pixel-for-pixel accurate screen grab above), I feel like I should wipe the mud away or get corrective lenses to view the Quartz text (and no, I don't need corrective lenses, my near sight is fine). Generally, the Quartz rendering obliterates font detail at such sizes. For example, serifs are easier to spot and discern on the ClearType text sample.
Halo, it's not just for Xbox
Generally, Quartz seems to raster fonts unnecessarily thick so it can apply what looks like a pseudo-sloppy, Gaussian blur filter resulting in fuzzy "halo" looking text. Now at larger sizes, this may make some sense, but on the smaller fonts (14 Point and smaller) it seems to decrease legibility. Fonts at small sizes particularly benefit from increased resolution, and ClearType seems to excel beyond Quartz in "creating" usable sub-pixel resolution by applying anti-aliasing more discriminately and not over-blurring the results. Perhaps a pseudo MultipleMaster's approach to sub-pixel rastering might be more optimal, where the "halo" effect is reduced for fonts at smaller sizes and increased at larger sizes.
So why did Apple implement a "halo" anti-aliasing model (when ClearType and Adobe's Acrobat text anti-aliasing seem more exacting)? The answer may lie in patents over the technology. If Apple cannot obtain a license on Microsoft's low resolution (i.e., small font size) sub-pixel rendering techniques, then we may simply have to wait until April 10, 2020 (when Microsoft's patent runs out).
Apple may actually posses a license to this technology as part of Microsoft's US$150 million investment back in 1997. However, it's uncertain that their patent portfolio cross-licensing agreement encompasses technology made after 1997. If Apple has a free license to this technology, then it should certainly use it; not employing the Microsoft, sub-pixel, rastering techniques at (least at) smaller sizes in Quartz might boil down to hubris. Regardless, Apple should continue to improve their display technology, perhaps through the use of ultra-high definition screens. Providing higher resolution displays would make the problem of over-blurred text at smaller sizes evaporate.
Screen display quality is important to the average person with regard to legibility. We read more and more on our computers. Reducing eyestrain can only help people. Further, display fidelity is crucial in the publishing industry, and improving its technology would only enhance Apple's position in the marketplace.