W3C home > Mailing lists > Public > www-style@w3.org > July 2000

Re: px vs. pt

From: Matthew Brealey <webmaster@richinstyle.com>
Date: Thu, 27 Jul 2000 13:57:19 +0100
Message-ID: <398031AF.54FC@richinstyle.com>
To: Rowland Shaw <Rowland.Shaw@seagatesoftware.com>
CC: www-style@w3.org
Rowland Shaw wrote:
> > > Pretty, but it is flawed by the fact you're example was/is using large
> fonts
> > > on a resolution intended for small fonts...
> >
> > What?
> > Why?
> > How do you know?
> Because your UA was assuming a screen resolution of 96dpi, which is used
> when the "large fonts" option is selected by the user in the Display
> Properties on the windows client.

No it's not. See http://richinstyle.com/small.png for a disproof.
> AFAIK, UAs rely on the same setting that wysiwyg text editors (eg. Word) use
> for computing font sizes, 

On which subject, Word is broken: see, for example,
http://www.freetype.org/docs/glyphs/index.html (section IV, part 4), an
excellent document that I recommend reading anyway.

> so you'd have to log a bug against them for
> displaying 'incorrect' font sizes...


What do you think they should use?
> So why bother with support for paged media in CSS? My original point was for
> the "best for all situations" solution, for which I think points are pretty
> useful, 

> and familiar to a lot of people starting up with webdesign from use


But that doesn't mean good.

> > And also, on a point of fact, pixels do translate well to print, since
> > they are rescaled (printers, unlike computers, have the required
> > information to do the necessary rescaling).
> Well, technically the printer doesn't know that much, it's some nice clever
> scaling either by the OS subsystems (Eg: Win GDI, which allows you to
> specify canvases in all sorts of measurement units), printer driver or even
> the UA (printing to Windows canvas in pixel mode doesn't "auto scale" for
> you)

Regardless, pixels are perfectly good for printing. They are also ok on
screen, which points are not.
> > > IMHO, physical sizes should be used for root elements, and relative
> sizes
> > > (in em or ex) for all the others...
> > I hope not. This is the height of rudeness on the part of the designer -
> > by doing this he maximises the problems, causing difficulties reading
> > for the greatest number possible. To counter this it would be useful if
> > browsers did proper rescaling of fonts (zooms are unsatisfactory):
> Would you like to back that up?
> 72pt is 72pt is 6picas is 1 inch is 25.4mm is 2.54cm is...

Is an arbitrary number of pixels that doesn't correspond to a real-world
value and therefore will look much larger/smaller on one machine
compared to another.

> Next, you'll be telling me that they are no WISIWYG word processors because
> they're all scaled incorrectly...

See above.
> > user without perfect sight sets font size in browser; e.g., 20px
> > user enables 'rescale fonts' option
> > Example:
> > rude developer creates page with font size of (say) 9pt.
> > Browser rescales font size to 20/16 * 9 * 96/72 = 15px.
> > Result: all accessibility problems caused by lazy/rude developers
> > disappear, and without the need for an annoying zoom feature (i.e. it's
> > automatic)
> I don't follow your argument in your example... 

It was a digression.
> > [Note there could be an 'advanced' dialogue box, where the figures I
> > suggest here (default font size, in pixels, of developer's computer (16)
> > and ppi value for that computer (96), which represent what most
> > developers/WYSIWYG editor makers use, could be changed.]
> Under Win systems: Control panel -> Display properties -> Settings -> Font
> size (small = 72 dpi screen res, large = 96dpi screen res)

Not the solution; this is merely a remedy to counter rude developers -
like the facilities that currently exist to adjust font sizes except
more useful.

> > In fact, to rebut your suggestion, no size at all should be used for the
> > root element, and relative sizes for all others. By using no size for
> > the root element, you respect the user's wishes as to size, rather than
> > inflicting upon them a size that is smaller than they an read. (BTW,
> > please read the page: exes are a BAD idea for font sizes.)
> I forgot percentages (sorry), which is what I would suggest for font sizes,
> reserving em and ex for things like padding, margins etc.

No, ems are fine. Ems are the same as % on font-size so it makes no
difference (although em is less buggy in the browsers to which it can
safely be served; i.e. if you are using browser-detection (preferably
non-User-Agent-header dependent), it is better to use ems for

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Received on Thursday, 27 July 2000 08:57:56 UTC

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