The other reason why OT/CFF fonts are smaller has to do with the much reduced hinting information contained in them (compared to TrueType fonts) - which brings me to the second benefit. This method will also decrease the font file size, but the reduction is not as significative as with subroutinization. The TrueType format also has a mechanism that allows turning a given glyph into a component which can then be reused by other glyphs - think of the glyph representing the letter A being reused in the glyph for the letter Á (A with acute accent). The more regularized the glyphs are, the more compact the font will be. Subroutinization is a process that surveys all the glyphs in the font looking for path segments that are identical and thus can be replaced by a shared routine/command. For those of you unfamiliar with the term, CFF stands for Compact Font Format (PDF file) and the compactness of a CFF font is in part achieved via a technique called subroutinization, which is performed when the font file is generated. So what makes OT/CFF fonts smaller? One of the reasons lies in the compact way in which the outlines are stored. And if you think about CJK (Chinese, Japanese, Korean) fonts which contain tens of thousands of glyphs and files ranging around 5–10 MB, size considerations become quickly obvious. Nevertheless, you’ll have to agree that smaller font files are surely desired for fonts used in web pages, fonts used in resource-limited devices, or a combination of both: fonts delivered to and displayed by portable devices. After all, modern hard drives are big enough and font files are actually some of the smallest assets in a project, especially when compared to print-resolution images, video files or even the artwork files themselves. But what if I tell you that on average OT/CFF font files are 20% to 50% smaller than comparable TrueType fonts? Does that grab your attention? Sure, you can still think it’s not that important. While the qualities mentioned above may give a bit of an edge to OpenType/CFF, I’m certain that they won’t persuade everyone.
This conversion, if not done properly, may result in distortions to the outlines.
Many of the designs available in TrueType format may actually have started their life as PostScript outlines - type lingo for cubic Béziers - and were converted at some point in the process. I would say that the majority of type designers prefers to use cubic Béziers because they’re easier to manipulate and are able to represent a wide variety of curves with fewer points than quadratic Béziers. Cubic Bézier (left) and quadratic Bézier (right).
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