iTherm
®
280 Programmer’s Guide ITherm® 280 Unicode and Fonts
28-07764 Rev C Page 259
point selection and not on the actual character height of any given characters. Second
guessing the font designer can have very bad results when character are encountered that use
the full cell.
Asian fonts require slightly different rules for character placement and are not as one would
expect. The Asian ideographs are positioned on center of mass, rather than on a baseline. The
Latin data in Asian typefaces must be built on the same rules. As a result, when Latin
characters are scaled the expected baselines do not line up. Asian fonts are also fixed pitch,
however, Latin character in the font are basically ½ the width of the typical Asian character.
Character Size
The character generation engine used in the ITherm 280 internally uses a standard point based
system to specify the character size. One point is 1/72 of an inch. Therefore a 72 point
character would form a character suitable to generate one line per inch printing. The typical
application might refer to a 12 point character. This is the character height and not the width.
The character width typically varies on character by character bases; for example, the lower
case “i” is much narrower than the upper case “W”.
Font selection commands for selecting character sizes in legacy applications are also
supported. For printers such as the ITherm 280, two or three character sizes are generally
predefined with a dot matrix size of 10x24 or 13x24 dots, and this fixed size may then be double
or tripled to provide larger characters when needed. To supply legacy support, the ITherm 280
will automatically select the appropriate character size to support the legacy font and character
scaling commands.
In the ITherm 280, the horizontal and vertical point size may be set independently. Typically
this type of printer would print a tall, narrow, mono-spaced character. Tall narrow mono-spaced
character provides a very readable print with easy column alignment while using less paper than
standard type fonts. This type of font is sometimes referred to as a condensed font.
Selecting Character Size
The ITherm 280 provides two ways to specify character size. The legacy or classic font
selection method is based on dot matrix size. The second method is based on the standard
type points system. The advantage of the type point system is that the print produced by the
printer will match what is displayed by the host system, as both use the same system for
describing the characters produced.
Legacy or Classic Method
With the classic method, the application selects a character size and then sets the character
spacing by adding or removing dot spaces between the characters. Using the scaled font, the
ITherm 280 provides 3 basic predefined character sizes. The smallest is a 10x24 dot-like
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font
and is typically printed in pitches from 16 to 20 characters per inch (CPI). The next larger font is
13 x 24 dot-like, and is typically printed in pitches from 14 to 16 CPI. The largest font is 14 x 24
dot-like font and is typically printed at pitches from 10 to 14 CPI.
The ITherm 280 always prints at 203 dots per inch (dpi) and always uses the scalable font to
form characters. The resulting characters are not necessarily exactly the dot size indicated, but
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Characters are dot-like because they are not guaranteed to be exactly at an exact dot equivalent. They
are spaced in a fixed character cell that provides equivalent spacing and alignment as a fixed character
size, however the actual character size is defined by the font designer.
