Quote:>TT hinting is lower level and more primitive than T1 hinting.
>And there is no automated way to translate from one to the other.
>In fact, font conversion utilities drop the original hints and generate
>new `auto' hints for the output format. Automatically generated
>hints are never as good as carefully hand-tuned hints. For a start,
>most auto-hinting does not support hint replacement --- which for
>some glyphs is crucial.
You're right that TT hints and T1 hints cannot be directly compared - they're
not the same things. But if you take "font + ATM", or "font + printer", as the
complete hinting entity, then TrueType can emulate their behaviour exactly.
Quote:>Yes, *theoretically* programming at a very low level allows you to
>do anything you want, but at the same time this generality makes it
>hard to do what is really needed in hinting.
>One `advantage' of TT hinting is that you can control individual pixels at a
>given ppem (pixel per em) resolution. The disadvantage is that you have to!
>The biggest labour in TT hinting is to control `drop outs' (missing pixels).
>You have to look at all glyphs in the font at all ppem you expect any user
>to ever use and check for these and knock them out individually.
>T1 rasterizing does not create drop-outs (unless you purposefully mis-hint!).
I examined some TrueType fonts from Bitstream recently, looking for the TrueType
instructions DELTA (move ranges of points or control values), MPPEM (measure
ppem) and MPS (measure point size). I understand these are the only ones that
mean glyphs are treated differently depending on their PPEM. Although I must
stress this was nothing like an exhaustive search, I didn't find those
instructions in any of the glyphs I looked at. The instructions present were
generally concerned with moving, aligning and interpolating points.
However, in the 'prep' font table, which contains instructions to be executed
before the scan conversion of each glyph, I found the SCANCTRL instruction.
Together with its parameter of 0x0164, this means: "always to do dropout control
below 100 (=0x64) pixels per em". In this mode, the TT rasterizer performs much
like a Type 1 rasterizer.
Quote:>Which is why there are very few properly hinted TT fonts --- except from the
>big boys --- namely MicroSoft (who is apparently getting out of the font
>business) and Apple.
I am sure Bitstream would argue their fonts are "properly hinted". In the
absence of any TrueType hinting police, one has to judge by the results. In my
experience Bitstream's TrueTypes are inferior on screen to Monotype's, but
certainly no worse than ATM fonts.
One point that does favour Type 1 over TrueType is the adaptability of the fonts
to future technology. New hinting techniques (such as that which sadly died with
Sun's F3 format), can be built into forthcoming PS rasterizers and exploit the
existing declarative hints to the full. Dumb, mechanical TrueTypes are committed
to supplying precisely the same glyph bitmaps until the end of time.
Accountants of the world! Don't forget to depreciate your TrueTypes!!
-- Laurence Penney