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<HTML>
<HEAD>
<!-- Created with AOLpress/2.0 -->
<!-- AP: Created on: 3-May-2001 -->
<!-- AP: Last modified: 29-Oct-2001 -->
<TITLE>Hinting</TITLE>
</HEAD>
<BODY>
<H1 ALIGN=Center>
Hinting
</H1>
<P>
Postscript originally required that hints should not overlap. Now it requires
that any active set of hints be non-overlapping, but it allows you to change
sets as you move through the character.
<P>
So to implement hinting with hint substitution PfaEdit needs to know not
only the position and width of the stem being hinted, but also where the
stem should be active. And it needs to know what stems overlap which other
stems.
<P>
<IMG SRC="Hints.png" WIDTH="406" HEIGHT="399" ALIGN="Left"> The horizontal
stems are drawn in light green. The vertical stems are drawn in light blue.
The areas where the stems are active are filled in as rectangles, outside
of that area the stems' outlines are drawn with dotted lines. Most of these
stems do not conflict with any other stems, but two, the bottom two horizontal
stems conflict with each other. All the non-overlapping stem hints may be
active at the same time, but only one of the two conflicting stem hints may
be active. As PfaEdit outputs the character it decides at each point what
stems need to be active, and activates them.
<P>
Postscript now allows PfaEdit to control relative counter sizes. Counters
are the spaces between adjacent stems. In the example at left there are two
counters of equal sizes on the between the horizontal stems on the left,
and three counters of equal sizes on the right. These form two independent
counter groups, and PfaEdit will generate a counter description for each
of them (Postscript allows type designers to specify the relative importance
of different counter groups. PfaEdit is not this sophisticated, counters
are output in left to right (bottom to top for vertical) order.
<P>
Counters spaces appear between vertical stems too, and in this case Pfaedit
would output one counter group for the vertical stems.
<H2 Clear=All>
Serifs
</H2>
<P>
<IMG SRC="serif.png" WIDTH="248" HEIGHT="227" ALIGN="Right">One of the major
advantages of hint substitution is that it allows certain standard serif
situations to be described. In the example at right, the serif one the left
is smaller than the stem a bit further right.
<P>
<IMG SRC="serif2.png" WIDTH="158" HEIGHT="110" ALIGN="Left">But it doesn't
solve all problems (or I don't know how to use it to do so). Consider the
serif on the right. Hint substitution would allow us to define a hint for
the main vertical stem and for the short vertical stem that corresponds to
the serif. But the problem that needs to be solved is making the distance
between the left edge of the serif and the left edge of the stem be the same
as the distance between the right edge of the stem and the right edge of
the serif. But doing so would require overlapping hints, active at the same
time. <SMALL>I think</SMALL>
<H2>
Manual Hinting
</H2>
<P>
I hope that the PfaEdit's autohint command will be good enough that manual
efforts will not be needed. But hopes are rarely fulfilled.
<P>
The AutoHint command should find all stems in a character. Some of them it
deems to be useless and will remove them. If you find that PfaEdit is removing
a hint that you think is important then invoke Hint->AutoHint with the
shift key held down, this will tell PfaEdit not to prune any of the stems.
You may then use Review Hints to prune things yourself.
<P>
If you find that you must create your own hints, PfaEdit will only allow
you to specify the position and width of the hint, it will then go off and
try to guess the extents where the hint should be active.
<H2>
Hints and previously existing fonts.
</H2>
<P>
PfaEdit will not be able to read hint info out of a TrueType font at all
(the format is too complex, there are too many posibilities). From a Type1
font without hint substitution it will happily read all the hints in a character.
In a Type1 font with hint substitution it will read some random subset of
the hints, and will mark the font as in need of having its hints regenerated.
In an OpenType (Type2) font PfaEdit will read in all the hints, but it will
have to figure out by itself where those hints are active (it will not read
that from the font file).
<H2>
Hinting and TrueType
</H2>
<P>
Hinting TrueType fonts opens a far wider range of posibilities. I have added
several types of hints that are specific to truetype (and will be ignored
by the postscript generation routines). These by no means exhaust the
capabilities of TrueType, I'm working on another tool for TrueType hinting,
called <A HREF="TtfMod/index.html">ttfmod</A> (it doesn't do much yet though).
<UL>
<LI>
Diagonal Stem Hints<BR>
These look similar to the horizontal and vertical stem hints that postscript
understands but they allow you to constrain the width of diagonal stems as
well.
<LI>
Minimum Distance Hints<BR>
TrueType allows you to say that the distance between two features should
never vanish. Every stem hint will automatically have one of these across
it, but there may be other places where they will be useful. In particular
you can insure that there is always white space after a character by putting
a minimum distance hint between a point on the right edge of that character
and the width line, also these hints can be used to solve the serif problems
mentioned above.
<LI>
Round to Grid<BR>
TrueType can move points to the rasterization grid before rasterizing characters.
Stem hints and minimum distance hints will automagically be rounded, but
there might be other cases where rounding is useful.
</UL>
<H2>
Examples of Minimum Distance Hinting
</H2>
<P>
<TABLE BORDER CELLPADDING="2">
<TR>
<TD><IMG SRC="Ehinted.png" WIDTH="189" HEIGHT="208"></TD>
<TD><IMG SRC="EhintedTtf.png" WIDTH="127" HEIGHT="145"><BR>
<SMALL>A fully hinted glyph is<BR>
completely grid fit, but<BR>
the difference between<BR>
stem lengths is lost.</SMALL></TD>
</TR>
<TR>
<TD><IMG SRC="Efore.png" WIDTH="188" HEIGHT="208"></TD>
<TD><IMG SRC="EforeTtf.png" WIDTH="127" HEIGHT="145"><SMALL><BR>
One attempt to solve the<BR>
above problem, compare<BR>
to below.</SMALL></TD>
</TR>
<TR>
<TD><IMG SRC="Eback.png" WIDTH="189" HEIGHT="208"></TD>
<TD><IMG SRC="EbackTtf.png" WIDTH="127" HEIGHT="145"><SMALL><BR>
Note how the different<BR>
directions in the md hint<BR>
change the rasterization</SMALL></TD>
</TR>
</TABLE>
<H2>
Hint questions:
</H2>
<P>
I find the hint documentation inadequate for me to do a good job at hinting.
<UL>
<LI>
Do I need hstem hints at top and bottom of a character for blue values to
be looked at?
<LI>
Section 2.4 of
<A HREF="http://partners.adobe.com/asn/developer/pdfs/tn/5015.Type1_Supp.pdf">T1_Supp.pdf
</A>says that vertical counters are offset from the lbearing, but the example
2.6 shows them being offset from 0.
<LI>
In
<A HREF="http://partners.adobe.com/asn/developer/pdfs/tn/5177.Type2.pdf">Type2</A>
is it ok to use Counter mask if LanguageGroup is not 1 and the stems don't
fit into a *stem3 pattern? Or can cntrmask only be used for *stem3 in latin
letters?
<LI>
<IMG SRC="NoPointHint.png" WIDTH="194" HEIGHT="232" ALIGN="Right">How do
hints work? Is a hint meaningful if there are no points associated with it?
As in the "O" at right, where the two vertical stems have no points associated
with them.
<LI>
Is it meaningful for a hint to have points only on one side of it? Can reasonable
hints be written for the serif cap above left?
</UL>
<P>
<A HREF="overview.html#Hints">Overview of Hinting in Postscript and
TrueType</A>.<BR>
<A HREF="hintsmenu.html">Hinting menu.</A>
</BODY></HTML>
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