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What is ClearType?

ClearType is a software technology developed by Microsoft that improves the readability of text on existing LCDs (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.

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.

How did Microsoft come to develop ClearType?

ClearType builds upon a tradition of dedication to high-quality font technology at Microsoft. Since the early nineties, Microsoft has continued to improve its display and font capabilities, including the further development of TrueType font technology originally licensed from Apple. Looking to further improve Microsoft's font rendering technology, 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.

How does ClearType display technology work?

To understand how ClearType works, one first has to understand what makes an LCD screen different from other types of displays. Most screens created images made up of pixels, which when magnified look like single squares. The equivalent of one pixel on an LCD screen is actually composed of three sub-pixels: one red, one green, and one blue (R-G-B). Seen together, these sub-pixel triplets combine to be seen by the human eye as a single pixel.

Magnification of a pixel.

If we were to look at a single pixel, our eye would see it as in the illustration above. However, if we were to magnify the image, we would see that each pixel is actually made up of three separate subpixels. And so, if when we see white on an LCD screen, we are really looking at red, green and blue stripes.

Magnifying a section of a color LCD screen.

How does this help improve the quality of digital type display?

Traditional computer font rendering assumes that each pixel is either 'on' or 'off', appearing as tiny black squares. Letters appear jagged on the computer screen because they are formed from many of these tiny squares or pixels. Traditional grayscaling assumes that each pixel has no internal structure, so it smooths the jagged edges but sacrifices edge sharpness. ClearType knows that LCDs are made up of colored sub-pixels. ClearType uses a model of the human visual system to choose the brightness values of the sub-pixels. With ClearType, letters on the computer screen appear smooth, not jagged, yet the edges remain sharp.

ClearType font rendering

Example of ClearType font rendering.
  1. This is how the lowercase 'm' looks in the original typeface outline.
  2. This is a close-up of the 'm' when rendered on screen without ClearType. Notice how the 'm' has hard, jagged stair-steps or 'jaggies' in the stems, or 'legs' of the 'm'.
  3. This is a close-up of the 'm' when rendered on screen with ClearType. Notice how the 'jaggies' are much more subtle and the letter is rendered more smoothly.

Comparison of ClearType and non-ClearType text rendering.

ClearType font technology works with current displays. Readability on CRT monitors will be improved somewhat, but it will be dramatically improved on color LCD monitors, such as those found in laptops and high-quality flat desktop displays.

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Last updated 16 January 2002.


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