Re: Rasterizer differences win98/XP

Jan Bruns wrote:
> I have a CRT-Monitor, so "ClearType" wasn't enabled

As in, you couldn't select it? That's odd. I've seen it used on CRT
monitors plenty of times...

> You mean n sampling points, all vertically at the pixels center,
> horizontally weighted by distance to center?

Essentially, yes. More precisely, 2*n-1 sampling points, all
vertically at the pixel's center, horizontally spaced by 1/n pixels,
with relative weights of n*(1-abs(x)) where x is the horizontal offset
from the center of the pixel in pixels. After a quick inspection of
text generated with MS Paint on my brother's WinXP machine, it would
appear that n=3.

Also, I retract what I said earlier about the grid-fitting. It would
appear that grid-fitting is in fact still used, but with a finer
horizontal resolution (to match the fine horizontal spacing of sampling
points).

> It also widens the font horizontally.

This is either a side-effect of your CRT monitor, or this is a more
accurate representation than you're used to seeing, due to finer
horizontal resolution.

I've put together an image demonstrating ClearType:
http://www.geocities.com/therealbirdin/Graphics/dog.png
Along the left edge is various text sizes represented at 1:1. Then
there are several blow-ups of the text at a few sizes. On the bottom
is a literal representation (though a bit dim overall; nothing I can do
about that in this case) of the ClearType presentation of 12-point text
on an LCD screen, and then that same representation but bled out
horizontally to achieve the intended brightness and to demonstrate what
the unaided eye basically sees on an LCD monitor.

Now getting back to your original question, it would seem that
ClearType is not the difference you originally noticed, considering you
said it was disabled. I still suspect that your font was subjected to
grid-fitting in Windows 98, but not in XP. I think I read somewhere
that fonts are supposed to specify at what sizes to do gridfitting, and
at what sizes to do greyscale. Maybe your font didn't contain such
information, and was therefore subject to the defaults built into the
rasterizers, which apparently differ between Windows 98 and XP.
Indeed, upon closer inspection, Windows 98's font smoother only
produces 3 shades between text and background color, wheras your sample
produces 15. But I hesitate to say that the Win98 algorithm uses only
2x2 samples per pixel, because if that were true then the 1/4 and 3/4
shades would be almost absent from near-horizontal or near-vertical
edges, yet they are as abundant as the 1/2 shade.

*shrugs*

--
David Smith
a.k.a. Vid the Kid

.

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