Monday, November 2, 2009

Auto-switching profiles for different displays

Some time ago a Jon sent me a nice postcard. It contained a link to his blog where he wrote about aut-changing the display profile when an external monitor is connected. He wrote a lot about it here. I also had this problem frequently on my Thinkpad T60, so I will probably try this out.

Short summary: The IBM presentation director can run commands on a display setup change, which could also be used to change the profile by a dedicated xcalib commandline.

Sunday, November 1, 2009

Unexpected xcalib applications #3: improving readability

I personally like command line terminals with a black background and white (or even green) text. However, this is not the most readable color combination and may stress one's eyes after long working sessions. In addition visually impaired people may also like to tweak the screen just for better readability.

There are two posts I've stumple across, which deal with readability. On the Adobe forums one suggested that Adobe Reader may need a feature to invert the page, i.e. to exchange background and foreground, here: The poster complains that reading PDFs is like having a bulb in front of you, which seems a valid point.

Another post comes from the Vinux development blog, here: Vinux is a special linux variant for visually impaired people. One issue for people with bad vision is wrong contrast. Hence, they propose using xcalib for applications like brightness and contrast control using keyboard shortcuts and in addition for an inverted copy of the primary screen on a second monitor, so that one can use the monitor that is more readable.

Unexpected xcalib applications #2: fixing brocken screens

There was one post on the Ubuntu forums that I didn't expect is a possible application for xcalib: fixing a brocken screen. You can find the original post here and the solution is here.

I didn't know that a screen can become completely inverted after it was dropped on the floor, but well, I just hope that this never happens to me. Nevertheless, the solution can either be to use compiz and invert everything or you can just use xcalib with the -invert switch. This switch I've added just for fun because I wanted to see whether it's possible to set arbitrary values in the video LUT. The interesting observation there was that X11 does not check the values, whereas on Windows the operating system does not allow you to set completely unlikely screen calibration values. Hence, this will only work on Linux:

xcalib -invert -alter

When you are going to do color-critical work (which I don't recommend with a knowingly broken screen!) and wanto to create an ICC profile, be careful: many calibration tools reset the LUT to the default values (the equivalent of xcalib -clear) - which are totally useless in this case to derive an ICC profile. Hence, better explicitly disable screen calibration in this case!