In the previous article, I explained about how horizontal and vertical hints work to control stroke thickness and position. Another major role of hints is to “arrange heights.”

A lot of characters in Latin fonts are designed in accordance to guidelines, such as the baseline (reference line) and cap height (uppercase letter height). However, not all characters fit perfectly within that line. Rounded characters, such as “O” and “C,” are designed to slightly extend (overshoot) beyond the baseline to prevent them from appearing visually smaller.

Although this protrusion is required for high-resolution printing, etc., slight difference can become noise on low pixel screen displays. Typically, only some characters appear to stick out one pixel above or below.

The mechanism to prevent this from happening is setting items called “BlueValues” and OtherBlues,” which define the “alignment zone (alignment range).” BlueValues defines main heights, such as the baseline and cap height, etc. OtherBlues defines the lower parts of lowercase letters, such as g and j.

The rasterizer uses BlueValues/OtherBlues as a reference, and processes “slight protrusion (overshoot) within the range by ignoring and flattening it on screen for display purposes.” Through this processing, even when displayed at small sizes, the character heights are arranged to the pixel level, making the text easy to read.

By the way, some of you may be wondering, “Why Blue?” I wondered that, too. I had conducted research on it before, and I have conducted research on it again this time, but I still don’t really understand it. Adobe’s technical material states: “For historical reasons, these hints are indicated by names that contain the word ‘Blue’.” However, “historical reasons” alone doesn’t really answer the question, does it? If you know the correct answer, please let me know.

（mm）