From: mmwang@adobe.com (Michael Wang)
Newsgroups: comp.lang.postscript
Subject: Re: Postscript Font Scaling & Reduction
Date: 20 Nov 92 02:04:24 GMT
Distribution: na
Organization: Adobe Systems Incorporated

ab@nova.cc.purdue.edu (Allen B) writes:
>zisk@adobe.com (Stephen Zisk) writes:
>>     4.) The reasons for different designs at different sizes in hot type
>>         (and Multiple Master Fonts) are complex and subtle:
>
>As far as I've seen, in most cases it was for mechanical
>reasons (as the poster said).  Trouble is, some people
>expect it now.  "Hysterical raisins." :-) 

I don't believe having different designs at different point sizes was
done for mostly mechanical reasons. There are some definite
readability and legability issues involved with optical scaling. While
typeface readability and legability is still mostly guesswork rather
than a science, there are areas where we do have good information. And
one of those areas is how the size of the type affects r&l.

For reading long passages of text, there is a small range of sizes
that gives the best balance between reading speed and reading
comprehension. What the "optimum" size is for a particular face may be
open to debate, but the general concept holds true. If it wasn't then
everything would be printed at 6 point and we could save millions of
trees a year.

As the point size gets smaller than this optimum size, reading
comprehension begins to suffer because it becomes more difficult to
discern individual words and letters. Conversely, as the point size
gets larger, reading speed suffers since instead of reading groups of
words at a time, you start to focus on individual words or letters.

To compensate for these problems, type designers in the past created
slightly different designs for different point sizes. At smaller
sizes, generally the x-height was enlarged, contrast between strokes
decreased, width of the various letters increased slightly and the
letterspacing was looser. At larger sizes, the opposite was done. The
effect of all these changes was to try and make those sizes more
readable.

For those technical minded people, another way of thinking about this
problem is to pretend that our reading "visual acuity" can be plotted
in the shape of a Gaussian curve with visual acuity being the y-axis
and point size the x-axis. At the middle of the curve, we have our
"optimum" point size for reading. As the point size decreases, we slip
down the left side of the curve and reading comprehension, or overall
visual acuity, suffers. By making the changes mentioned above, we make
the typeface at that size appear "bigger" and so we move slightly back
towards the middle, improving comprehension. Similiarly, as the point
size gets larger, we slip down the right side of the curve, decreasing
the reading speed. If we tweak the face to appear "smaller" at that
size, we shift back towards the middle again.

With photo typesetting and now digital typesetting, you can look at
stuff at a small size that has been linerally scaled from a single
design and think it looks pretty readable. What you don't realize,
unless you have had experience in this area, is that with optical
sizing, things can look even better.

-- 
Michael Wang
mmwang@mv.us.adobe.com