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#1 2010-05-02 19:56:35

correnos
Member
Registered: 2009-11-05
Posts: 20

How to adjust brightness/contrast with xorg/intel?

I have been unable to find any info on how to change the brightness or contrast with the intel gma drivers. Is this possible?

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#2 2010-05-02 20:21:42

lagagnon
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From: an Island in the Pacific...
Registered: 2009-12-10
Posts: 1,087
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Re: How to adjust brightness/contrast with xorg/intel?

I assume you mean on a laptop screen and not a desktop monitor? Because if the latter then use the Monitor's menu system. Otherwise I use "xbacklight" with an Intel chip, works fine. You might have to bind xbacklight to a key sequence if your laptop's function keys don't work properly:
http://wiki.archlinux.org/index.php/Extra_Keyboard_Keys

If xbacklight does not work please privde more detail, ie video chip number and laptop model #.


Philosophy is looking for a black cat in a dark room. Metaphysics is looking for a black cat in a dark room that isn't there. Religion is looking for a black cat in a dark room that isn't there and shouting "I found it!". Science is looking for a black cat in a dark room with a flashlight.

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#3 2010-05-02 20:48:17

correnos
Member
Registered: 2009-11-05
Posts: 20

Re: How to adjust brightness/contrast with xorg/intel?

Running xbacklight comes back with

No outputs have backlight property

My laptop's a dell studio 1555 with an intel gma 4500MHD. I'm not fussy about having it bound to a certain key, but having it working would be nice.

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#4 2010-05-02 21:56:30

combuster
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From: Serbia
Registered: 2008-09-30
Posts: 711
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Re: How to adjust brightness/contrast with xorg/intel?

That issue was fixed a long time ago, there shouldn't be any problems on intel igp's. Does echo 5 > /sys/class/backlight/acpi_video0/brightness as root changes the backlight level ? You can see available values with cat /proc/acpi/video/GFX0/*/* , maybe 5 is too small value if it goes up to 100 for example...

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#5 2010-05-02 22:09:57

correnos
Member
Registered: 2009-11-05
Posts: 20

Re: How to adjust brightness/contrast with xorg/intel?

There are no files in /sys/class/backlight, but the front buttons for brightness work fine. That's not the problem I'm trying to solve, however. I am trying to change screen contrast.

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#6 2010-05-03 01:44:03

lagagnon
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From: an Island in the Pacific...
Registered: 2009-12-10
Posts: 1,087
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Re: How to adjust brightness/contrast with xorg/intel?

Most laptops do not have a contrast hardware control. You would need to use facilities provided by the Intel video driver itself, and I understand that facility is not available with the Intel drivers, but have a browse here:
http://intellinuxgraphics.org/index.html

You can adjust contrast with the nVidia and ATI Linux drivers, but not Intel, AFAIK....


Philosophy is looking for a black cat in a dark room. Metaphysics is looking for a black cat in a dark room that isn't there. Religion is looking for a black cat in a dark room that isn't there and shouting "I found it!". Science is looking for a black cat in a dark room with a flashlight.

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#7 2010-05-03 01:51:41

correnos
Member
Registered: 2009-11-05
Posts: 20

Re: How to adjust brightness/contrast with xorg/intel?

that matches what I've seen so far. Ah well...

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#8 2010-05-03 04:59:07

Jodell
Member
Registered: 2009-10-09
Posts: 285

Re: How to adjust brightness/contrast with xorg/intel?

combuster wrote:

That issue was fixed a long time ago, there shouldn't be any problems on intel igp's. Does echo 5 > /sys/class/backlight/acpi_video0/brightness as root changes the backlight level ? You can see available values with cat /proc/acpi/video/GFX0/*/* , maybe 5 is too small value if it goes up to 100 for example...

Has it really been fixed? It never worked for me with an Intel GMA 4500 hmm

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#9 2010-05-03 06:36:16

ewaller
Administrator
From: Pasadena, CA
Registered: 2009-07-13
Posts: 18,321

Re: How to adjust brightness/contrast with xorg/intel?

Okay, I cannot resist.  In my previous day job, I worked on broadcast video equipment.  In the current day job, we build high performance LCD displays that go into some very hostile environments.

On a television, what is it that brightness and contrast control?  The answers are simple:

"Brightness" controls the black level.  If set too low, pixels that are not supposed to be black will be black.  If set too high, pixels that are supposed to be black are somewhat gray. The proper way to adjust this on a CRT TV is using a color bar with a bright pluge in the lower right hand corner.  On a computer LCD display, the proper way to set this is to display a pattern with gray steps and adjust the brightness such that the first bar (black) is not visible, but such that the second bar is and is distinguishable from the third.   On a LCD, this is not generally a problem in that when all zeros are sent to the shutters, it is as black as it is going to get.  Some drivers will allow clipping of the digital signals at the low end, but all that really does is clip things that are not supposed to be black to black.

"Contrast" on a TV actually controls the gain of the luminance (black and white part of the picture).  The contrast should be adjusted such that a  gray step pattern does not saturate to white until the last step in the pattern.  The second to last step should be distinguishable from the last.  Again,in an all digital system, this should not be an issue, but could become an issue if one is still using a VGA system.

As an aside, the "Color" control is the chrominance gain and controls the color saturation whereas "tint" (only on NTSC) controls the phase of the color subcarrier (PAL and SECAM avoid this by changing reversing the phase on every other line)

Then comes the backlight issue.  In most LCD systems, the Luminance is a function of both the backlight level and the individual shutters.  The real definition of contrast can be simplified as a ratio of the display luminance to the amount of ambient light reflected from the display.  In low light conditions, it is easy to get a high contrast display (>1000:1), whereas the same display in high ambient light may be lucky to achieve 3:1.  The only way to drive up that contrast ratio is by improving the display luminance (either by increasing backlight brighness or by improving the transmittance of the LCD.

Even more fun, the transmittance of an LCD is a strong function of viewing angle.  Generally, LCD manufactures will express the size of their viewing angles as those angles where the display will achieve 3:1 or 10:1 (depending on the manufacturer) contrast ratios in a low light, indoor environment.

So, what were we trying to achieve? Oh yeah -- contrast and brightness.  Set the display such that blacks are black, slightly gray is not black, white is saturated, but almost white isn't.  Then, to improve contrast, drive the backlight hard, and reduce ambient light


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#10 2010-05-03 12:06:01

chakra-user
Member
Registered: 2010-03-07
Posts: 74

Re: How to adjust brightness/contrast with xorg/intel?

Does any one know how to change brightness and contrast of Desktop LCD on Intel onboard graphics card? I am using Viewsonic VA1913wm LCD monitor.

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#11 2010-05-03 12:43:08

Ultraman
Member
Registered: 2009-12-24
Posts: 242

Re: How to adjust brightness/contrast with xorg/intel?

Yes, you do that with buttons on your monitor or inside the OSD (menu) of your monitor.
Looking at a picture of your monitor now, googled it, looks like you have 5 buttons on there, so check it out. Probaly inside the Menu option.

More ontopic:
I also have a Intel GMA 4500MHD, in my laptop, and the sysfs entires did not work for me. Normally using the Fn keys did not change my brightness either. The inputs are detected as something like XF86BrightUp and XF86BrightDown key presses by X, but the brightness of the LCD does not change. So the keys are being recognized, the adjustment of the brightness doesnt happen.
I looked into this and discovered I can control brightness by altering a register using the "setpci" command. How to do this can be found on the web, but if you have difficulty, ask here and i'll look it up on my laptop. If I don't reply, I might have missed this topic bumping up, in that case just send me an email via the board.

I now use a small script in combination with the acpi daemon (acpid). When that detects the according key events, it runs the brightup or brightdown script. Those scripts read the register value (hex) to a variable, change the variable up or down accordingly and then use setpci to set the new value, which changes my screen brightness. Works great smile

Last edited by Ultraman (2010-05-03 12:53:12)

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#12 2010-05-03 16:01:58

chakra-user
Member
Registered: 2010-03-07
Posts: 74

Re: How to adjust brightness/contrast with xorg/intel?

Ultraman wrote:

Yes, you do that with buttons on your monitor or inside the OSD (menu) of your monitor.
Looking at a picture of your monitor now, googled it, looks like you have 5 buttons on there, so check it out. Probaly inside the Menu option.

Ofcourse I know that. I was asking if I could control via Software. Manually using buttons is anybody's guess.

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#13 2010-05-03 16:15:38

litemotiv
Forum Fellow
Registered: 2008-08-01
Posts: 5,026

Re: How to adjust brightness/contrast with xorg/intel?

chakra-user wrote:

Ofcourse I know that. I was asking if I could control via Software. Manually using buttons is anybody's guess.

the intel windows drivers do offer contrast (per channel), but the linux drivers don't support this as of yet. you could send intel a support request for this, maybe they are working on it.


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