font scaling (was: Re: Using Computer Modern in Lout - some final questions)

[Vadim Nasardinov]

On Thursday 28 August 2008 12:20:51 am Clint Olsen wrote:
> > By the time you have converted your font to an AFM file, it is no
> > longer a 10p font.  The AFM format describes the abstract shapes
> > of the glyphs without specifying any particular font size.  There
> > is a convention that a length of 1000 in the AFM file represents
> > the font size; but it does not represent any *particular* font
> > size.
>  
> Ok, so why then do they bother creating all these various AFM files
> corresponding to different sizes from Metafont?  Is it because the
> font characteristics don't scale optically and vary with different
> sizes?

Correct.



To lift a couple of quotes...


A Plain TeX Primer, by Malcolm Clark
http://www.amazon.com/Plain-TEX-Primer-Malcolm-Clark/dp/0198537247/
p.32:

 | ... These are all 10 point sizes.  What does that mean?  One way to
 | create typefaces is with reference to a `design size'.  Or put
 | another way, this particular font was designed to be seen at a
 | particular size.  Had the designer been concerned to have the
 | typeface used at a different size, she or he would have designed
 | another face, more suited to that particular size.  This is a
 | somewhat idealized viewpoint.  At a practical level, designers
 | sometime create typefaces which may be `the same' over a range of
 | sizes, designing perhaps four or five subtly different designs to
 | cover a typical range from 4pt to 72pt or bigger.  The real purist
 | would argue that even two faces 1 point different in size ought to
 | be designed differently.  But life is too short.  Some typefaces
 | are merely magnified over their entire range.  This is probably an
 | oversimplification, but for many reasons it is a solution popular
 | with the manufacturers of typesetting equipment.  TeX adopts both
 | solutions, as we shall see later...

TeX for the Impatient, by Abrahams, Berry, and Hargreaves [1990]
(ISBN: 0-201-51375-7)
http://www.tug.org/texlive/Contents/live/texmf-doc/doc/english/impatient/book.pdf
p. 54:

 | Fonts can be provided either as outlines or as bitmaps. An outline
 | font describes the shapes of the characters, while a bitmap font
 | specifies each pixel (dot) that makes up each character. A font
 | outline can be used to generate many different sizes of the same
 | font. The Metafont program that's associated with TEX provides a
 | particularly powerful way of generating bitmap fonts, but it's not
 | the only way.
 | 
 | The fact that a single outline can generate a great range of point
 | sizes for a font tempts many vendors of digital typefaces to
 | provide just one set of outlines for a typeface such as Palatino
 | Roman. This may be a sensible economic decision, but it is an
 | aesthetic sacrifice. Fonts cannot be scaled up and down linearly
 | without loss of quality. Larger sizes of letters should not, in
 | general, have the same proportions as smaller sizes; they just
 | don't look right. For example, a font that's linearly scaled down
 | will tend to have too little space between strokes, and its
 | x-height will be too small.
 | 
 | A type designer can compensate for these changes by providing
 | different outlines for different point sizes, but it's necessary to
 | go to the expense of designing these different outlines. One of the
 | great advantages of Metafont is that it's possible to parameterize
 | the descriptions of characters in a font. Metafont can then
 | maintain the typographical quality of characters over a range of
 | point sizes by adjusting the character shapes accordingly.