W3C home > Mailing lists > Public > www-style@w3.org > December 1998

platform-specific font size issues

From: Todd Fahrner <fahrner@pobox.com>
Date: Tue, 15 Dec 1998 10:42:38 -0800
Message-Id: <v04020a06b29c5db83462@[]>
To: www-style@w3.org
Since before Mosaic, the default font size value in all major browsers has
been set at 12pt. I propose redefining the default as 16px. This will
affect only browsers for the Mac OS.

The current default of 12pt rasterizes very differently across platforms.
On Macs, it rasterizes into 12px (logical res fixed at 72ppi). On Wintel
PCs, it rasterizes by default into 16px (logical res defaults to 96ppi). I
am unfamiliar with X11 default behavior(s). All scalable font-size values,
such as the CSS keywords "small", "large" etc., as well as em or percentage
values and the legacy font tag attributes, operate relative to this
inconsistent base rasterization.

For a designer, this means that the *only* way to suggest an
x-platform-consistent font size is to use CSS pixel units, which are not
user-scalable, and are thus not optimally user-friendly/portable. Never
mind that CSS pixel units have been implemented with some severe bugs in
IE3 and Nav4, making them dangerous for general use.

All other means of influencing font size - CSS keywords, percentage or em
measures, font tag attributes, big or small tags - all are virtually
guaranteed to produce divergent results x-platform. This is a designer's
nightmare. Usually the user loses, because the designer's choices are to
force consistency by turning text into image or using nonscalable CSS pixel
units, or to accept variance and optimize for the dominant PC rendering
defaults. In the worst case of all, the designer will use point units,
which are neither user-scalable nor x-platform consistent.

Severe bugs in the implementation of CSS pixel units mean that designers
tend to specify font size in either points, keywords, or relative measures.
I am fairly confident that the most common font size specifications on the
Web today reduce the size of text to one or two steps below the default, on
the unfortunately often valid assumption that most users do not adjust the
Windows-default 16px, and prefer the results of having it adjusted downward
for them.

Because the rasterization semantics for all such "smaller" values defaults
to a much lower pixel count on the Mac, however, the Web is becoming less
and less legible to Mac users. Since MSIE4 for Windows shipped with no
top-level UI to adjust font size, the problem has worsened. Designers who
are aware of the issues tend to create more images of text to avoid the
problem - also unfortunate.

The appropriate corrective measure, I submit, is for Mac (and X11?)
browsers to break with tradition and ship with the default value of
"medium" text set at 16px, instead of 12pt. This should of course remain
subject to user adjustment, but a consistent initial value will at least
make the use of scalable font-size values less problematic for designers,
as any variance from the default will be due to express user preference
rather than capricious legacy OS differences.

If designers tend to believe that 16px is too large as a base, why suggest
it as the default?

1. Pure expediency: the Mac is a smallish minority platform, though very
strongly represented in the Web design field (I use a Mac!). It is
unrealistic to expect that Windows/X11 browsers will change their defaults
to match the Mac's rather quaint limitation to 72ppi logical resolution.

2. The 1996 CSS1 standard suggests a 1/90" value for a "reference pixel",
extrapolated from a visual angle of 0.0227 degrees visual angle at arms
length. UAs are expected to scale pixels appropriately if the physical
resolution is known to vary significantly from this value. A 1/90"
reference pixel would suggest a rasterization of 12pt into 15px, rather
than 16. 15 is of course much closer to 16 than to 12, however. Because no
OS/UA currently assumes a 90ppi logical resolution, (nor implements
pixel-scaling per CSS1), I think the reference pixel value should be
amended to 1/96". It's simple to preserve the suggested 0.0227 degrees
visual angle by giving the reference user a longer arm's length. (^:

3. Designers think that 16px is too large simply because they are used to
the 12px base size of their Macs. Readability is 9/10ths familiarity.
Todd Fahrner                    The printed page transcends space and time.
mailto:fahrner@pobox.com        The printed page, the infinitude of books,
http://www.verso.com/agitprop/  must be transcended. THE ELECTRO-LIBRARY.
                                                   - El Lissitzky, 1923
Received on Tuesday, 15 December 1998 13:47:32 UTC

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