These problems are a result of the absolute and finite size of the pixel. These irregularities detract substantially from the legibility and overall attractiveness of a textsetting. At low resolutions, with few pixels available to describe the character shapes, features such as stem weights, crossbar widths and serif details can become irregular, inconsistent or even missed completely. Scaling an unmodified outline's control point co-ordinates to the small sizes of a computer screen can result in severe quality control problems. TrueType enables the designer to stipulate exactly how the glyphs and their spacing will appear at low resolutions in isolation as well as within a textsetting. Because the outlines are only distorted at a specified number of small sizes, the contours of the letterforms at higher resolutions remain unchanged, and undistorted.Īlthough many font formats and applications offer some hinting facilities, these hints typically consist of a few global parameters that are only capable of specifying distances that should be kept the same. Grid-fitting explicitly ensures that certain features of the glyphs are regularized, and allows us to overcome many of the problems traditionally associated with displaying text at low resolutions. Now the outline has been adjusted to fit snugly around each pixel, ensuring that the correct pixels are turned on. Note how poorly the outline corresponds to the pixel pattern, and above all how awkward the bitmap of the M is.įigure 1b. This outline adjustment is carried out on a case-by-case basis and is illustrated in figure 1 below.įigure 1a. On the basis of the instructions contained in the individual font file, the TrueType rasterizer adjusts the glyph outlines to fit the bitmap grid appropriate for whichever size the text is to be displayed at. Modifying an outline in this manner results in what is known as a grid-fit. In TrueType a combination of these hints, and the resulting distortions, affords a very fine degree of control over the bitmap shape produced. Technically, hints result in operations which modify a contours' scaled control point co-ordinates before the outline is scan converted. A hint is a mathematical instruction added to the font to distort a character's outline at particular sizes. Since it is a glyph's outline that determines which pixels will constitute a character bitmap at a given size, it is often necessary to modify the outline to create a good bitmap image in effect modifying the outline until the desired combination of pixels is turned on. What is Hinting?Īt its most basic level hinting (or, more accurately, instructing) a font is a method of defining exactly which pixels are turned on in order to create the best possible character bitmap shape at small sizes and low resolutions. As a means of demonstrating the power of the TrueType format, several examples are shown here which compare TrueType fonts side-by-side with equivalent PostScript Type 1 fonts rendered by the ATM rasterizer. This paper explains exactly what hinting is, why it is necessary, and how the TrueType approach to hinting differs from the approaches adopted by other font formats. Well-hinted TrueType fonts are consequently the best fonts when it comes to displaying text on the screen. The TrueType font format offers far more power and flexibility in its hinting capabilities than other font formats. Moreover, because the bitmaps are still produced by an outline font, text can be rotated, scaled and viewed at different sizes, and even printed out while maintaining high image quality. A well-hinted font offers the quality only provided in the past by hand-tuned bitmaps - but with all the speed and reduced memory requirements which characterize outline font formats. It is indispensable in every font intended to be legible at small sizes on low resolution output devices. Hinting is an essential part of the production of a quality font.
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