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Re: gzip vs. mtx compression ratios

From: Thomas Phinney <tphinney@cal.berkeley.edu>
Date: Tue, 30 Jun 2009 00:16:03 -0500
Message-ID: <f49ae6ac0906292216h6efc0262ja036a9067f61613c@mail.gmail.com>
To: John Daggett <jdaggett@mozilla.com>
Cc: www-font@w3.org
Hmmm. Hard to make suggestions without knowing what all you have
access to. Let's discuss off-list...



On Mon, Jun 29, 2009 at 11:56 PM, John Daggett<jdaggett@mozilla.com> wrote:
> Hi Thomas,
> Any examples you would suggest?
> Cheers,
> John
> ----- Original Message -----
> From: "Thomas Phinney" <tphinney@cal.berkeley.edu>
> To: "John Daggett" <jdaggett@mozilla.com>
> Cc: www-font@w3.org, "Philippe Le Hegaret" <plh@w3.org>, "chris" <chris@w3.org>, "Vladimir Levantovsky" <Vladimir.Levantovsky@monotypeimaging.com>
> Sent: Tuesday, June 30, 2009 1:45:46 PM GMT +09:00 Japan
> Subject: Re: gzip vs. mtx compression ratios
> That's quite interesting. But for general fonts in the wild, neither
> system fonts nor the ClearType C-fonts are very representative. They
> are all hand-hinted, which makes them unlike 99% of TrueType fonts out
> there.
> It would be interesting to see the results on some typical TrueType
> fonts that have been autohinted by (1) Fontographer 4.x and (2)
> FontLab Studio 5. That would tell us a bit more.
> Regards,
> T
> On Mon, Jun 29, 2009 at 2:05 AM, John Daggett<jdaggett@mozilla.com> wrote:
>> I sat down a little today and played around with font compression.  I
>> tested compression ratios of gzip vs. MTX, the MicroType Express
>> algorithm used as part of the Microsoft EOT format.  The spreadsheet
>> below contains charts and a summary of the data I collected:
>> https://spreadsheets.google.com/ccc?key=rKT_wNzraVrkXQcKSWb-jTA&hl=en
>> I used Microsoft's WEFT tool to create unsubsetted EOT versions of each
>> font and compared it with the gzip-compressed version of the font file.
>> As Vlad noted before, standard webfonts such as Times New Roman, Arial,
>> Georgia and Verdana compress to file sizes 20-28% smaller than the size
>> of files compressed with gzip.  However, fonts in the Cleartype font set
>> that Microsoft commissioned for Vista are only 11-14% smaller.  These
>> fonts use less hinting than traditional TrueType fonts and rely on
>> Cleartype screen rendering to render glyphs clearly.  This is important
>> because it seems indicative of a trend towards more lightly hinted
>> TrueType fonts, which would indicate the hint-related compression that
>> MTX provides won't be needed as much going forward.  But MTX for these
>> fonts still does a better job than plain gzip compression.
>> For large CJK fonts however, where compression is most needed, MTX
>> doesn't provide much beyond straight gzip compression.  For Meiryo, EOT
>> files are 17% smaller but for other CJK fonts the range was only 2-12%.
>> In fact, using bzip2 general compression beat font-specific MTX for
>> several of these fonts.  These numbers are also probably distorted in
>> favor of MTX because the fonts were in TrueType collection files (.ttc)
>> rather than straight .ttf files, so there are extra glyphs in the gzip
>> file that aren't in the EOT version.
>> Since the WEFT tool doesn't handle Postscript CFF fonts (.otf)
>> currently, I tested the MTX compression of these fonts by merging CFF
>> data from other .otf fonts into a TrueType font, then comparing the
>> differences in the resulting compressed versions.  The MTX compression
>> seemed to be around 5% better than straight gzip.  Although this doesn't
>> account for compressed metrics, I think this is pretty close to the
>> compression that a version of MTX modified to compress CFF glyph data
>> would see.
>> In summary, MTX seems to compress older TrueType fonts well but less so
>> more modern lightly-hinted fonts.  It is a little bit better than gzip
>> for CJK fonts but lags behind general bzip2 compression in many
>> instances.  For .otf fonts it's only slightly better than gzip
>> compression.
>> Regards,
>> John Daggett
>> Mozilla Japan
> --
> "Men occasionally stumble over the truth, but most of them pick themselves up
> and hurry off as if nothing ever happened."
> - Sir Winston Churchill

"Men occasionally stumble over the truth, but most of them pick themselves up
and hurry off as if nothing ever happened."
- Sir Winston Churchill
Received on Tuesday, 30 June 2009 05:16:40 UTC

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