Re: down the LCD panel rabbit hole

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On 08/10/2009 09:35 PM, Tim wrote:
On Mon, 2009-08-10 at 19:38 -0400, brian wrote:
I'm also pretty confused as to why there are 2 separate display config
panels in the first place.
System preferences - set up drivers and configuration for what your
hardware actually is.

User preferences - allows users to have custom resolutions to suit
themselves, such as users with eyesight problems who want everything
big.  If a user doesn't set their own preferences, the default is to
give them the highest resolution available.
I sort of understood it that way. My confusion was mainly that the two
resolution select lists didn't seem to correspond. I see, now, that it
was because my xorg.conf was messed up. Or, I assume that was it.
One thing, though: when I finally got it right (see my other response)
the resolutions selected were both different as well as being a lot
lower than the max.
Though, LCDs only work well at their physical resolution.  Even exact
multiples of double or half resolution look disgustingly smudgy.  CRT
monitors often work well at several different resolutions, they don't
have 1:1 mapping of graphics pixels to the dots of screen phosphors.
Which would explain why it was so blurry earlier. It looked pretty
miserable.
You also mentioned frame rates.  It's usual that LCD panels only work at
one frame rate (60 Hz being common), compared to CRTs which often work
across a few different rates.  Most graphics cards have an array of
different screen sizes and frame rates, with there being combinations of
some of them that they cannot do (e.g. it may do high resolution *or*
fast screen rates).  If your card only offers your desired resolution at
a different frame rate that your monitor users, you can't use that
screen mode.  That's why some people find that their desired resolution
is unavailable to them.
The manual for this panel lists:

Mode, H Freq. (kHz), V Freq. (Hz), Pixel Clock (MHz), Sync Polarity (H/V)

640 x 350 	31.47 	70.09 	25.18 	+/-
640 x 400 	31.47 	70.09 	25.18 	-/+
640 x 480 	31.47 	59.94 	25.17 	-/-
640 x 480 	31.50 	75.00 	31.5 	-/-
720 x 400 	31.47 	70.08 	28.32 	-/+
800 x 600 	37.88 	60.32 	40.00 	+/+
800 x 600 	46.880 	75.00 	49.50 	+/+
1024 x 768 	48.36 	60.00 	65.00 	-/-
1024 x 768 	60.02 	75.03 	78.75 	+/+
1152 x 864 	67.50 	75.00 	108.00 	+/+
1280 x 1024 	63.98 	60.02 	108.00 	+/+
1280 x 1024 	79.98 	75.02 	135.00 	+/+
1920 x 1080-R 	66.587 	59.934 	138.50 	+/-
1920 x 1080 	55.62 	49.92 	141.50 	-/+

I'd come across someone else's xorg.conf for use with this same LCD. However, their numbers (eg. dot clock) were slightly different. And I was stumped as to where xorg.conf's "HTimings hdisp hsyncstart hsyncend htotal" numbers came from. Rather than blindly follow along with this person's config, I eventually found a reference to the cvt utility. I ran:
cvt 1920 1080 55.62

... to get those figures.

This is just for posterity in case someone else needs the info.

Thanks for the reply, btw.



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