Re: OS X Preview -- wrong size
Re: OS X Preview -- wrong size
- Subject: Re: OS X Preview -- wrong size
- From: Robert Clair <email@hidden>
- Date: Fri, 25 Feb 2005 08:45:54 -0500
This doesn't appear to be a Quartz API, it's a tech note code fragment,
hence doesn't appear in the Quartz reference documentation.
(See <http://developer.apple.com/qa/qa2001/qa1217.html>.)
You are, of course, literally correct - my mistake. But what's the
difference ? The information is accessible to developers with a little
digging. (And Cocoa developers need to know how to dig. Cocoa is
wonderful but the documentation is, to be charitable, a bit skimpy in
places.)
If the display is at 90 PPI. 72 x 1.25 = 90.
If the display is at 72ppi it will measure 1". 72 x 1 = 72.
What's the mystery?
There is no mystery - you just need to go to the effort of obtaining
the dpi, or a reasonable guess, and scaling the coordinate system.
Historically most people haven't bothered to do this. The size
disparity annoyed me, so I took the time to do it. The price was
asking people to enter the DPI as a preference - with 100 as the
default. (The above code fragment was broken when I started.)
You can, of course vary the physical size of the image on a CRT by
tweaking the controls - but unless you are having a bad day the change
in size by doing this is usually small compared to the difference
between 72 dpi and 90 or 100. A "typical" number for a CRT would be
better than 72.
Bob Clair
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