On Windows XP, text is rendered as grayscale by many browsers. Although not as crisp as the subpixel rendering used by Mac OS, the letters are nicely smoothed and look great in large sizes.
TrueType font rendering with Windows GDI ClearType.
ClearType is Microsoft’s take on subpixel rendering. It was first made available for GDI, the classic Windows API. Although available in Windows XP, it is not used by all browsers. In Windows 7 and Vista, ClearType is the default, which makes it the most widely used rendering technology (if we were to consider all internet users). However, it is important to note that this applies only to TrueType-based Web fonts—GDI-ClearType is not applied to PostScript-based fonts.
One curious property of this rendering technology is that along with adopting the advantages of subpixel rendering in horizontal direction, Microsoft gave up smoothing in vertical direction entirely. So ClearType is effectively a hybrid of subpixel and black-and-white rendering. This results in steps within the contour, which is particularly noticeable in large sizes. These jaggies at the top and bottom of the curves are unpleasant, but unavoidable—even the best hinting cannot make them disappear.
For type in large sizes, ClearType is a step backwards in rendering quality. The gains in horizontal precision are not significant, while the rough contours spoil the overall result.
TrueType font rendering with DirectWrite.
The future is bright, at least in terms of Windows font rendering. In DirectWrite (the successor of GDI), Microsoft added vertical smoothing to ClearType. This new rendering mode (so far used by Internet Explorer 9), gives us smooth and precise rendering in all sizes. The main difference to Mac OS that remains is that it still tries to align contours to full pixel heights, which leads to even better rendering given that the font is well-hinted. What’s more, DirectWrite allows for subpixel positioning, which gives the characters exactly the spacing that they have been designed with, improving the overall rhythm and evenness of the texture.
Windows: PostScript Fonts
PostScript font rendering with GDI grayscale.
In GDI-based browsers, PostScript-based Web fonts are displayed in grayscale. Unlike the prevalent GDI-ClearType, this gives smooth contours. And unlike TrueType hints, PostScript hinting is easier to create, even automatically.
PostScript font rendering with DirectWrite.
DirectWrite not only gives smoother outlines, it also applies subpixel rendering to PostScript fonts. Unlike TrueType rendering, however, it allows for more gray pixels in order to reflect stroke weights more realistically. That makes it well-balanced, and similar to Mac OS rendering.
At some point in the future—browser makers and users will not switch as quickly as we wish—DirectWrite will succeed the older Windows rendering methods, and we will indeed be spoilt for choice between TrueType- and PostScript-based Web fonts.
Windows: Unhinted Fonts
Unhinted font rendered with grayscale.
In the old Windows grayscale mode, completely unhinted fonts look surprisingly good. Since the font does not “align itself” to full pixels via hinting, and the rasterizer does not enforce this either, we have a rendering that is similar to that of iOS. Unfortunately, unhinted fonts are currently not an option, as the next example shows:
Unhinted TrueType font in GDI-ClearType rendering.
As noted in many discussions on Web font rendering quality, GDI-ClearType is extremely dependent on good hinting. Horizontal strokes have to be precisely defined by means of hinting, otherwise they might be rendered in an inappropriate thickness. Even in larger sizes, hinting is crucial. Unhinted fonts will show “warts” sticking out where contours are not correctly aligned to the pixel grid, like in the example above.
Unhinted font rendered with DirectWrite.
In DirectWrite, unhinted PostScript and TrueType-based Web fonts show virtually the same rendering. Text fonts of either flavor will still need good hinting in order to keep the strokes crisp and consistent. Display fonts may even get away with sloppy or no hinting, since this does not show much in large sizes. 出处:https://www.smashingmagazine.com/2012/04/a-closer-look-at-font-rendering/
