Introduction

Since people first start using bitmap font files to store fonts, the digital font industry has been through a long and success revolution. Technologies like Adobe's PostScript, Apple and Microsoft's TrueType and Microsoft's ClearType, are continuing to serve people in improving vision quality of the digital fonts on various media. In this project, I examined the colorfulness of the fonts rendered with ClearType font technology and investigated the seven parameters that determine the color artifacts being introduced to ClearType fonts. Why there will be color in black-and-white font? A brief introduction of ClearType is given below. You can find out about my experiments and results in corresponding sections. Some interesting conclusion could be found in conclusions section. Some codes are available in appendix.

What is ClearType Font Technology?

ClearType is a software technology developed by Microsoft that improves the readability of text on existing LCD (Liquid Crystal Displays), such as laptop screens, Pocket PC screens and flat panel monitors. With ClearType font technology, the words on your computer screen look almost as sharp and clear as those printed on a piece of paper. (figure 3)

Orignially, fonts are stored in hand-tuned bitmap font files that specified individual pixel locations for a font at a particular size. As you can see in figure 1, the problem with that, is when we scale the smaller size into the bigger ones, the font will suffer from the blocking-effect. Soon, both Adobe and Apple released their solution to the bitmap font problem - the outline font. Apple has the TrueType. The idea is to use curves and lines to describe font outlines, a.k.a. glyphs. In this representation, fonts can be scaled to pretty much any arbitrary size. (figure 2 )The translation process from curve and lines to pattern of dots on the media is also called 'rasterization'. However, this doesn't work all the time, i.e. small fonts will suffer from illegibilty at low resolutions. Font hinting technology is then introduced. Then came the anti-aliasing technology, whcih smoths the edges of the fonts at the expense of a slight blurring. In late 90's, after Microsoft got the license of TrueType from Apple, the researchers exploits the pixel structure of TFT LCD based displays to increase the apparent resolution of text and invented sub-pixel rendering technology. Microsoft has marketed these technologies particularly heavily, and they are now widely used on all platforms. (figure 3) Microsoft's ClearType ignores many hints, and works best with "lightly hinted" fonts.

	1. Bitmap font technology: individual pixel locations are stored 2. Outline font technology: use curves and lines to describe the outline 3. ClearType font technology: increase the apparent resolution

Understanding ClearType

First off, to understand how ClearType works, one has to know that LCD do not really have full-color pixels. The pixels in an LCD are arrayed in vertical stripes with red sub-pixels displaced 1/3 of a pixel to the left of green and blue sub-pixels 1/3 of a pixel to the right.

The highlighted pixel (below) is how a white pixel appears with magnification; the highlight pixel (above) is a partially turned on LCD pixel.

Traditional display algorithms ignored such physical properties of the display device and forfeited the resolution enhancement provided by ClearType. ClearType works by accessing the individual vertical color stripe elements in every pixel of an LCD screen. Before ClearType, the smallest level of detail that a computer could display was a single pixel, but with ClearType running on an LCD monitor, we can now display features of text as small as a fraction of a pixel in width. The extra resolution increases the sharpness of the tiny details in text display, making it much easier to read over long durations.

Project Objective

ClearType is great, but not perfect. If you look closely on the screen, you can actually notice the color artifacts around the edges. My project is to use S-CIELAB to investigate how various parametes determines the colofulness of the fonts rendered with ClearType font technology.

More Stories Behind Smoother Texts

ClearType works because human vision is much more sensitive to variations in intensity than it is to variations in color, i.e. the human eye can discern contrasts in intensity about three times better than it can discern contrasts in color. Thus, when ClearType sacrifices color accuracy in order to improve the sharpness of light and dark, the overall effect - as seen by human eyes - is an improvement.

Microsoft researchers spent more than two years sifting through a large amount of research related to both typography and the psychology of reading. They concluded that reading is a form of pattern recognition. People become immersed in reading only when word recognition is a subconscious task and the conscious mind is free to read the text for meaning. What was discovered is that word recognition is only subconscious when typographical elements such as the shape and weight of letterforms, and the spacing between letters work together to present words as easily recognized patterns. With these findings in mind, Microsoft began taking a closer look literally at how type was being rendered on screens

© 2007 jiajing