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OutputQuality
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1991-06-09
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Output Quality
Legality
--------
Copyright 1991 by Michael Jansson. All Rights Reserved.
This file is a part of the vfont distribution. It may only be
distributed in companion with the other parts of the vfont
distribution. It may be freely distributed for non-profitable
purposes only.
Introduction
------------
This font machinery is so far, at some extent, fulfilling two
of the goals I set up when I started this project; speed and
power. The most important goal is, however, good looking
rendered characters.
This file contains some notes about quality, some hints of what
kind of quality you can expect and how you can achieve it.
Creating small fonts
--------------------
Writing a font machinery for a computer screen is much hard
than writing such a beast for a printer due to the difference
in resolution. A normal sized character on a page is usually
10 points high, which is roughly equal to 30 pixel on a decent
printer or laser writer. Re-scaling a font that was designed
at 1000x1000 to the size 30x30 will lead to a character that
look a bit "rough". Re-scaling a font that was designed at
1000x1000 to the size 8x8 will lead to a ridiculous result! The
poor result has nothing to do with round-off errors in the
computation, but on the fact that a mathematically correct scaled
font is NOT what will look best.
An example; Assume that the font machinery is about to re-size
a character "O". Assume that the character is defined by a
number of coordinates, which are given in a floating point
format with sufficiently high precision. Assume that all
calculation is done in this floating-point format, and then
finally rounded to the nearest point on a raster. It is now
easy to see that there are sizes where this method will
give a character that has a left side that is wider/thinner
then the right side, due to the discreet raster.
Hinting
-------
So what was the problem with the above method? Absolutely
nothing! The font machinery can only produce as good result as
it is mathematically possible WITH THE GIVEN DATA. The key
thing here is that quality can be improved if there are
information that the font machinery can use to preserve
symmetrical aspects of characters. It basically boils down to
using some extra data to "cheat" when doing the transformation
to the raster, such as saying "every point that is near enough
to the baseline should probably be on the baseline". This is
known as HINTING, and has been used with amazing results on
many font system.
The vFont machinery are only supporting hinting in a very
limited way. What is the effect of this then? Well, don't
expect any mind blowing results of heavily scaled fonts. You can
still achieve very good result if you follow the following rule;
use a font class that was designed for a size that is close to
the desired font size.
Creating good looking small fonts
---------------------------------
Opening a bitmap font with the xdf_diskfont library and using
the font at the original size will give you EXACTLY the same
quality as if you would have used that font with the ordinary
graphics functions.
Creating good looking large fonts
---------------------------------
Opening a vectorized font (FontoGrapher, vfont etc.) at fairly
large size (say 32 pixel high, or higher) will also give you
quite good results.
Creating no-good looking fonts
------------------------------
Attempting to look at a vectorized font as a small font, or
looking at a bitmap font as a large font will result in a poor
result.