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. 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. 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. 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 is a form of sub-pixel font rendering that draws text using a pixel's red-green-blue (RGB) components separately instead of using the entire pixel. When the pixel is used in this way, horizontal resolution theoretically increases 300 percent. Picture elements on an LCD screen are actually comprised of individual horizontally-oriented red, green and blue sub-pixels. For instance, an LCD screen that has a display resolution of 800x600 pixels actually has 2400x600 individual sub-pixels. The human eye is not capable of differentiating colors on such a small scale, so a combination of these three primary colors can emulate any intermediate color. Sub-pixel font rendering takes advantage of this by antialiasing at the sub-pixel level instead of at the pixel level. No two screens are exactly the same and everyone perceives color in a slightly different way. To see if your screen is set to its native resolution, try looking at the following eye test image. The image is made up of many vertical black lines. If you see alternating bands of white running vertically through this image, you are probably running at a non-native resolution. I'm a type designer. How can I see how my fonts will render under ClearType without installing Windows? Type designers can license our Visual TrueType (VTT) font hinting tool. VTT was updated to let designers proof their fonts under ClearType. See VTT for more information. Want to try using Ask Learn to clarify or guide you through this topic?