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Re: Font Size discrepancies across platforms (was Re: Current Downloadable Font Status....)

From: Clive Bruton <clive@typonaut.demon.co.uk>
Date: Tue, 26 Aug 97 16:53:56 +0100
To: www-font@w3.org, www-style@w3.org
Message-ID: <872611003.0611421.4@[]>
Walter Ian Kaye wrote at 24/8/97 2:56 am

>No, Windows displays type LARGER than MacOS. I just threw together a page:
>   <http://www.natural-innovations.com/boo/dpi-doodoo.html>
>A Windows 9pt font takes the same number of pixels as a Mac 12pt font.
>This is because Windows *thinks* it is at 96dpi, while MacOS *mandates*
>that it is at 72dpi. (ppi, whatever)

I think you're confusing "larger" with pixels per em. I already covered 
that, obviously 12pt rendered for 96dpi (or any screen res higher than 
72dpi - Mac) will appear larger on a 72dpi, the reason is that it is no 
longer a 12pt typeface for that system.

12pt at 96dpi is 16ppm, while at 72dpi it's only 12ppm, obviously if you 
transfer one bitmap to another system its ppm isn't going to correlate 
with the notional rendered point size unless the screen dpi is identical.

> > being Macs that run higher res screens.
>QuickDraw *ALWAYS* assumes 72dpi, and images fonts accordingly. Your video
>configuration is irrelevant, as the OS has no idea how you manually adjusted
>the analog amplification controls on your monitor.

Well your screen settings are irrelevant in terms of the bitmap rendered, 
since the ppm is unchanged, however the physical size of the bitmap 
rendered to screen is dependent on the dpi of the monitor, it follows 
that twice the dpi gives a bitmap of half the physical size.

> > The problem seems to be of the OS or the browser understanding what a
> > point is, and that screen resolutions are variable (therefore
> > compensating for that). Then everyone will get type the same size, but
> > with different resolutions (effectively different pixel per em values)
>But how do you tell the OS what your video display LOOKS like? As far as
>I know, there are no CRTs with any ability to sense their *true* geometry;
>they only know if you increased or decreased something, and thus cannot
>report the true/actual/visible/physically-measurable dpi back to the OS.

I don't suppose it would be too much of a problem for someone to write a 
control panel to set the parameters correctly. As Todd ssems to be of the 
opinion that more Macs run at greater than 72dpi than don't (if I recall 
correctly), and I certainly wouldn't argue with that, it's about time 
someone sorted it out.

-- Clive
Received on Tuesday, 26 August 1997 12:02:57 UTC

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