ClearType Revealed
31 December 2001 Note: This article was originally written
for Infosync. Between leaving my job
and getting ready to move out of my apartment, I didn't have time to finish a
fresh column this week. Hope this is interesting to those that haven't
already seen it, and I'll be back with regular columns next week. JK It's time set the record
straight about the screens on the new Pocket PC 2002 devices. A lot of people
look at the 3.8 inch size of the screen on the iPaq and assume it must be
more readable than the 3.5 inch screen on the Jornada or the Casio E-200. As
it turns out, this is a faulty assumption. Bigger does not always mean
better. The Jornada and Casio screens are far more readable. Part of this is
the fact that the Jornada and Casio screens, while smaller, are the same 240x320
pixels as the iPaq, meaning that the pixels themselves are smaller and closer
together, increasing effective resolution. They have more pixels per inch
than the iPaq, so the screens look finer, smoother. But the biggest
difference is how the screens handle ClearType. What is ClearType? ClearType is a new name for
a fairly old technology. The concept of sub-pixel font rendering goes back to
the Apple II, and but it didn't really come into its own until the widespread
adoption of LCD screens. Essentially, it's a method of anti-aliasing text
that exploits the nature of LCD pixels to create the illusion that the screen
is higher resolution than it actually is. Anyone who's used "font
smoothing" in Windows is familiar with anti-aliasing. This is a
technique to smooth out the "jaggies" in on-screen type by
averaging out intervening values. For example, let's say you have a letter
"A". If you look really close, you'll see that due to the limited
screen resolution of your monitor, you can see the "stairstep" of
the black pixels against the white background along the slanted sides of the
"A". Anti-aliasing puts a gray pixel in each of these stairs, so
that when viewed from a distance, the letter looks smoother, less blocky and
jagged. Anti-aliasing works well for
larger type where the rendering engine has more pixels to work with, but on
smaller type, it just makes things blurry, since the extra pixels to
anti-alias the type equal or outnumber those of the original text. It doesn't
work very well at all for handhelds, because the text on handheld devices has
to be relatively small in order to fit a useful amount of it on a business
card-sized screen. Anti-aliased text on a monochrome Palm often ends up
looking more muddy than readable. Enter ClearType. Sub-pixel
anti-aliasing works a little differently. On a color LCD, each pixel is
actually made of three colored sub-pixels, one each of red, green and blue.
You can probably see this for yourself if you take a really close look at a
TV screen. Each dot is actually three tiny colored bars. The different
intensity of light that each bar emits determines how the human eye averages
them together to perceive a single color. With ClearType, the computer
addresses each bar individually when anti-aliasing text, resulting in less
blockiness and less blur, because the units used to build and smooth each
letter are so much smaller. The end result is that you seem to have almost
three times the linear resolution you had before, and the letters are crisp
and clear, even at smaller font sizes. Jornada/Casio vs.
iPaq All Pocket PCs support
ClearType. It's included with every copy of Microsoft Reader, after all, and
there are regsitry hacks to enable it in Pocket Internet Explorer or
system-wide, if you like. But ClearType doesn't work equally well on all
devices. On the HP Jornada and the
Casio E-200, the LCD screen is oriented so that the red, green and blue
sub-pixels are oriented horizontally when the screen is in portrait
orientation. When you hold the device in your hand, the bars that compose
each pixel move across the screen in the same direction you read the text.
This allows the screen to maximize ClearType efficiency, as you get the
three-times resolution boost in the same dimension that you're most likely to
notice a difference. ClearType letters on a Jornada are crisp, clear and
black, and it works so well that HP has even provided a checkbox in the
Screen Control Panel applet to enable ClearType system-wide, so you don't
have to track down any registry hacks to do it yourself. The Compaq iPaq is a
different story. The iPaq screens seem to be designed with a landscape
orientation in mind, the same as desktop monitors -- wider than tall. The LCD
elements on the iPaq screen are oriented so that they run horizontally only
when the device is in landscape orientation. When the screen is in portrait
orientation (the default), the LCD elements run vertically. ClearType
functions very poorly with this arrangement as most of the resolution boost
is lost between lines, and letters are smoothed in the wrong direction. Take a close look at text in
Microsoft Reader on a first-generation iPaq. Notice how the tops of the
letters have a bluish tinge? Notice how blurry everything is? It's even worse
on the new Pocket PC 2002 iPaqs, as it seems that ClearType in Pocket PC 2002
anti-aliases from left to right regardless of pixel orientation. This gives
letters a red fringe on the left and a blue fringe on the right, like you're
supposed to look at them with 3-D glasses. The bigger screen of the iPaq
may be great for video or gaming, but the smaller screens of the Jornada and
Casio Pocket PCs are clearly more readable. |