On Mon, 10 Jul 2006, Tim wrote:
On Sun, 2006-07-09 at 20:03 -0400, Tom Horsley wrote:
If I correctly set the DPI for my Westinghouse LVM-42w2
42" 1920x1080 dpi monitor, the setting is 52dpi, and at
52 dpi everyone seems to draw fonts that are somewhere
around 4 or 5 pixels high and mostly unreadable even
if you paste your eyeball to the screen :-).
Yep, you're stuffed, because the people providing those options haven't
understood the situation properly (those who design font rendering
engines, and those who get you to set font sizes in pixels in web
browser configurations). I get the same thing (stupid font sizes).
DPI means how many dots per inch, or pixels in that inch, will be used
to draw the character (how smooth the edges are). It has *NOTHING* to
do with how big the character should be drawn.
There's no magic about "points" either. There are 72 of them in an inch
and that's all one needs to know about them.
Geez, that problem was dealt with properly on printers ten years ago.
Changing your printer from 24 DPI to 48 DPI, for example, didn't change
the font sizes, unless the driver was written by a complete and utter
moron. You just got smoother looking fonts, at the same size.
Right. The printer just doubled the number of dots in an inch--it slowed
dot-matrix printers to half speed and used twice as much ink.
But the printer or its device-specific driver knows how wide/tall a sheet
of paper is and the DPI in any mode is fixed. So it's easy for the
printer or driver to know how many dots are in a point.
Displays can't change the number of dots in an inch. Display drivers
could prespecify the DPI, and I don't really know why they don't. But to
get accurate characters, the display driver needs to know the right number
of DPI (and that's really it). The same screen resolution (in pixels)
will have different DPI settings depending on the physical size of the
screen. 1280x1024 on a 17-inch CRT necessarily means more DPI than
1280x1024 on a 19-inch CRT and that's more than 1280x1024 on a 19-inch
LCD.
The font-scaling math converts, say, 8-point type (1/9-inch high) to the
best representation it can get given that there are 96 (or 52, or 84, or
114) actual pixels in an inch.
In this day and age of using scaled/vector type of fonts, for just about
everything, I don't know why this old, treat it like a bitmap, stupidity
still exists.
Ultimately, modern low-cost displays and printers *are* just bitmaps.
Even if the electron guns draw vectors like they did in the early days of
high-end graphics, the image is drawn on phosphors on the screen (pixels).
All the vector math is devoted to converting the vector description to the
best possible bitmapped rendering.
LCD displays have the additional ability to use the colored subpixels to
get even better effects. But to do the conversion accurately, one needs
to know how to map points to pixels, i.e., the true DPI.
--
Matthew Saltzman
Clemson University Math Sciences
mjs AT clemson DOT edu
http://www.math.clemson.edu/~mjs
