I love my new monitor. The colors are great, it's sharp, the angles
are good. Only one problem: it's really really bright.
It has the usual baffling "push buttons at random trying to figure out
how to navigate the menu system" brightness control -- which dims
the monitor's perceived brightness by about .003% if I take it all
the way to the bottom of the scale. (This is apparently a bug that
some of these Dells have and others don't.)
It has contrast, too -- but
the monitor won't change contrast when running through the DVI cable
(this is even documented in the monitor's manual).
I have no idea why. It makes me wonder whether there's normally a way
of changing brightness over a DVI cable; but lots of googling hasn't
brought enlightenment on that score.
I tried the VGA cable. The display was very noticeably less sharp,
though pressing the monitor's "auto adjust" improved it a lot.
Contrast adjustment did work (and helped) using the VGA cable,
but it also turned everything green. I was able to improve the
color cast a bit with
xgamma -ggamma .75 -bgamma .9
but this was all looking like quite a hassle. I wanted an easier way
to change brightness. xgamma wasn't it: it works well for fine-tuning
but its brightness curve is way off if you try to depart by much from
full brightness.
Enter xbrightness and
xbrightness-gui (Mikael Magnusson to the rescue again! He
knew about these excellent programs, and perhaps equally important,
he had a copy of xbrightness-gui, which seems to have vanished from
the web.)
xbrightness is an excellent little command-line program that sets the
X gamma curve to appropriate values. Just run xbrightness BRIGHTNESS
passing it a value between 0 and 65535. xbrightness-gui is an
interactive program that lets you drag curves around for each of
the three color curves, or the combined image, with a user interface
very similar to GIMP's Curves tool. You can even save and load curves.
xbrightness-gui's coolness notwithstanding, the simple xbrightness was
really all I needed. It does a fine job of adjusting the monitor
brightness while keeping colors neutral. The version I was using
was Mikael's version, to which he'd added the ability to adjust colors
too (much like xgamma does, but using more useful curves). It turns
out I don't need the color correction, but it's nice to know it's there.
But what I did need was a way to query the current brightness, and,
more important, a way to bump the brightness a little bit up and down.
So I added those features. Getting the current brightness isn't
actually something you can do, since the whole gamma curve for the
three channels is what you perceive as brightness. I didn't try to
estimate perceived brightness based on the whole curve; I just took
the value of the highest value for each color, and their average or
maximum.
Then I tied my new increment/decrement into key bindings in Openbox.
I bound W-F5 (the Windows key plus F5) to xbrightness -2560, and
W-F6 to xbrightness +2560, so I can go up or down in brightness by
pressing keys without having to type any five-digit numbers.
I've made available the old xbrightness-gui, since it's no longer
available anywhere else; a patch that integrates my changes and Mika's
into xbrightness-0.3; and the patched xbrightness tarball.
They're all at http://shallowsky.com/software/xbrightness/.
One other fun thing about using X gamma settings to adjust
brightness. The first night I used it, I noticed at some point that my
cursor looked very different -- it had become blindingly white.
It turns out that the cursor is implemented at a lower level and
doesn't go through the X gamma system. So turning the brightness
down via gamma curves doesn't affect the cursor, which remains always
at full brightness. It's quite a nice side effect -- the cursor is
much more visible than it normally is.
Tags: linux, monitor, brightness
[
11:37 Nov 26, 2008
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Dave and I recently acquired a lovely trinket from a Mac-using friend:
an old 20-inch Apple Cinema Display.
I know what you're thinking (if you're not a Mac user): surely
Akkana's not lustful of Apple's vastly overpriced monitors when
brand-new monitors that size are selling for under $200!
Indeed, I thought that until fairly recently. But there actually
is a reason the Apple Cinema displays cost so much more than seemingly
equivalent monitors -- and it's not the color and shape of the bezel.
The difference is that Apple cinema displays are a technology called
S-IPS, while normal consumer LCD monitors -- those ones you
see at Fry's going for around $200 for a 22-inch 1680x1050 -- are
a technology called TN. (There's a third technology in between the
two called S-PVA, but it's rare.)
The main differences are color range and viewing angle.
The TN monitors can't display full color: they're only
6 bits per channel. They simulate colors outside that range
by cycling very rapidly between two similar colors
(this is called "dithering" but it's not the usual use of the term).
Modern TN monitors are
astoundingly fast, so they can do this dithering faster than
the eye can follow, but many people say they can still see the
color difference. S-IPS monitors show a true 8 bits per color channel.
The viewing angle difference is much easier to see. The published
numbers are similar, something like 160 degrees for TN monitors versus
180 degrees for S-IPS, but that doesn't begin to tell the story.
Align yourself in front of a TN monitor, so the colors look right.
Now stand up, if you're sitting down, or squat down if you're
standing. See how the image suddenly goes all inverse-video,
like a photographic negative only worse? Try that with an S-IPS monitor,
and no matter where you stand, all that happens is that the image
gets a little less bright.
(For those wanting more background, read
TN Film, MVA,
PVA and IPS – Which one's for you?, the articles on
TFT Central,
and the wikipedia
article on LCD technology.)
Now, the comparison isn't entirely one-sided. TN monitors have their
advantages too. They're outrageously inexpensive. They're blindingly
fast -- gamers like them because they don't leave "ghosts" behind
fast-moving images. And they're very power efficient (S-IPS monitors,
are only a little better than a CRT). But clearly, if you spend a lot
of time editing photos and an S-IPS monitor falls into your
possession, it's worth at least trying out.
But how? The old Apple Cinema display has a nonstandard connector,
called ADC, which provides video, power and USB1 all at once.
It turns out the only adaptor from a PC video card with DVI output
(forget about using an older card that supports only VGA) to an ADC
monitor is the $99 adaptor from the Apple store. It comes with a power
brick and USB plug.
Okay, that's a lot for an adaptor, but it's the only game in town,
so off I went to the Apple store, and a very short time later I had
the monitor plugged in to my machine and showing an image. (On Ubuntu
Hardy, simply removing xorg.conf was all I needed, and X automatically
detected the correct resolution. But eventually I put back one section
from my old xorg.conf, the keyboard section that specifies
"XkbOptions" to be "ctrl:nocaps".)
And oh, the image was beautiful. So sharp, clear, bright and colorful.
And I got it working so easily!
Of course, things weren't as good as they seemed (they never are, with
computers, are they?) Over the next few days I collected a list of
things that weren't working quite right:
- The Apple display had no brightness/contrast controls; I got
a pretty bad headache the first day sitting in front of that
full-brightness screen.
- Suspend didn't work. And here when I'd made so much progress
getting suspend to work on my desktop machine!
- While X worked great, the text console didn't.
The brightness problem was the easiest. A little web searching led me
to acdcontrol, a
commandline program to control brightness on Apple monitors.
It turns out that it works via the USB plug of the ADC connector,
which I initially hadn't connected (having not much use for another
USB 1.1 hub). Naturally, Ubuntu's udev/hal setup created the device
in a nonstandard place and with permissions that only worked for root,
so I had to figure out that I needed to edit
/etc/udev/rules.d/20-names.rules and change the hiddev line to read:
KERNEL=="hiddev[0-9]*", NAME="usb/%k", GROUP="video", MODE="0660"
That did the trick, and after that acdcontrol worked beautifully.
On the second problem, I never did figure out why suspending with
the Apple monitor always locked up the machine, either during suspend
or resume. I guess I could live without suspend on a desktop, though I
sure like having it.
The third problem was the killer. Big deal, who needs text consoles,
right? Well, I use them for debugging, but what was more important,
also broken were the grub screen (I could no longer choose
kernels or boot options) and the BIOS screen (not something
I need very often, but when you need it you really need it).
In fact, the text console itself wasn't a problem. It turns out the
problem is that the Apple display won't take a 640x480 signal.
I tried building a kernel with framebuffer enabled, and indeed,
that gave me back my boot messages and text consoles (at 1280x1024),
but still no grub or BIOS screens. It might be possible to hack a grub
that could display at 1280x1024. But never being able to change BIOS
parameters would be a drag.
The problems were mounting up. Some had solutions; some required
further hacking; some didn't have solutions at all. Was this monitor
worth the hassle? But the display was so beautiful ...
That was when Dave discovered TFT
Central's search page -- and we learned that the Dell 2005FPW
uses the exact same Philips tube as the
Apple, and there are lots of them for sale used,.
That sealed it -- Dave took the Apple monitor (he has a Mac, though
he'll need a solution for his Linux box too) and I bought a Dell.
Its image is just as beautiful as the Apple (and the bezel is nicer)
and it works with DVI or VGA, works at resolutions down to 640x480
and even has a powered speaker bar attached.
Maybe it's possible to make an old Apple Cinema display work on a Mac.
But it's way too much work. On a PC, the Dell is a much better bet.
Tags: linux, tech, photo, graphics, monitor, S-IPS, TN, ADC, DVI
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20:57 Nov 15, 2008
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