[cairo-bugs] [Bug 10301] LCD filtering patch

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Thu Oct 2 09:51:34 PDT 2008


--- Comment #60 from belshazzar at gmx.net  2008-10-02 09:51:20 PST ---
> (In reply to comment #57)

Hello Carl. I very much agree with Nicolaus. I also understood that you were
not against the Turnerian FIR filters but against possible distributors’
choices affecting what Cairo can promise to render or not. Still I want to
point something out regarding which filter is better for Cairo.

> The filters in cairo were written with the assumption of strong hinting. And
> with that hinting, I still haven't seen any better filters, (freetype provides
> a "LEGACY" filter that's supposed to be similar---it's not identical but I
> don't know if one or the other would be "better" in my opinion). I do agree
> that there are really bad color fringes if you use this filtered sub-pixel
> rendering without good hinting. I think "just don't do that" would be that
> reaction of the original filter's author. :-)

But strong hinting is the wrong assumption to begin with. Full hinting — or
worse, byte-code superhinting — is so 1990’s!

Sure, a lot of coder/UNIX types still prefer high contrast on-screen text, but
for Cairo an algorithm that is so robust that it can accomodate both full
hinting and light autohinting is much a much better match.

Cairo is general purpose, so one thing it’s used for is on-screen text in UI
and, e.g., webpages. This is a setting where full hinting makes some sense,
because integer point sizes are used and the Cairo filter then has to deal with
1px stems only. No big deal, as only the curves and bowls and diagonals need

But Cairo is also used for freely scalable canvases, for rich graphics using
serif, script, or decorative typefaces. For animation. Strong hinting makes no
sense here. On a general image surface nice autohinted text blends in a lot
better. Autohinting /is/ »good hinting«. And the FIR filters are the best
match for it. Even better, the FIR filters even give very good results for
strongly hinted UI text. It’s just more versatile.

Please see the AB comparison page I made:
(Weakness: It only presents one case, one text setting, unlike the huge
comparison that Sylvain presented.)

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