Font Size in Open Office Docs on different platforms

[Matthew Saltzman]

On Tue, 29 Aug 2006, Tim wrote:

> Tim:
>>> Are the lines the same widths?  Point sizing generally refers to
>>> characters per inch across the page.
>
> Richard England:
>> I don't believe that is true unless it has changed since my days in
>> actual printing.  The character size in points refers to the size from
>> the highest to the lowest extent of the letters of a given type face
>> size.
>
> While the "size" of a font is, indeed, the entire size of the font,
> points used in typing, generally, were just used as a measure of how
> many would fit across a given width (10pt being the common one, 12pt
> being the more compact, usually).

A point is 1/72 of an inch, and typface sizes are measured vertically. 
Ten-point type is smaller than 12-point type.

Manual and electric typewriters of old usually came with one of two 
fixed-width typefaces: Pica (10 chars per inch) and the more compact Elite 
(12 cpi).  (High-school students liked Pica typewriters better than Elite 
because fewer words were needed to fill up that five-page essay.  Today's 
high-school students use the same trick.)  (Adding to the confusion, a 
pica is a measure equal to 1/6 of an inch.)

It doesn't make much sense with a variable-width font to talk about 
measuring its size in terms of horizontal cpi.

>
>> You also have to consider the display medium. DPI and aspect ratio of
>> the display device can wreak havoc on any document transfered across
>> systems.
>
> Another consideration that word processor document files are just
> storage of something on a particular PC (for later printing, etc.).
> They really are not a portable document format.  A different PC might
> have different fonts, and will probably have a different printer (with
> different minimum margins).

The problem of documents looking different on different systems is indeed 
due to fonts, at least in large part.  The different fonts usually differ 
in terms of appearance (of course) and in terms of average width.  Modern 
printers usually have controllable margins and one of a few standard 
dots-per-inch measures (and the information is recorded in the drivers), 
so that's not so much of an issue.  (Old daisy-wheel printers were another 
matter entirely.)  The issue is how typefaces are translated from their 
vector descriptions to their pixel representations.

With screens, fonts are measured in points, but when they are drawn, they 
are drawn using pixels.  The font-drawing systems need to know the true 
number of pixels per inch (ppi) in order to get the point size true.  If a 
system can't detect the ppi and the user doesn't set it, then the font 
sizes on screens are likely to be (a) wrong and (b) different from screen 
to screen--even when using the same software.

-- 
 		Matthew Saltzman

Clemson University Math Sciences
mjs AT clemson DOT edu
http://www.math.clemson.edu/~mjs