Jonathan's blog

I hadn’t realised how important it is to calibrate a monitor correctly.

My former method of “calibration” was simply to set the monitor’s contrast to maximum, and set the monitor’s brightness to a value that looked comfortable to me. I didn’t bother changing any settings in software.

But I got caught out.

Last night I took some photos and tweaked them on my PC so they looked OK. I published them and thought nothing of it. But several of my friends commented that they looked a bit dark, and when I checked the pictures out on two of the computers at work, they were indeed too dark.

My badly-calibrated monitors at home caused me to wrongly edit an image. So I read up on how to calibrate a monitor. There are many ways, but the method I’m writing about here is nice and simple.

• If you have TFTs, they are sensitive to the angle you look at them. Tilt them so they face directly at you.
• Turn the lights off in the room you are working in.
• On the monitor, set the colour temperature to 6500K
• On the monitor, set the contrast to 100%
• Look at the gamma black chart below. Adjust the brightness on the monitor until:
  • Bar A is just visible at the bottom
  • Bar B is visible from the bottom to about halfway up the chart


Gamma black chart

• Absolute black on your monitor is now calibrated.
• Find how to adjust the gamma on your computer. For example, I am running the proprietary nVidia X driver on Fedora and it comes with a convenient control panel. You can use Adobe Photo Shop to adjust the gamma, or xgamma under X Windows on Unix/Linux systems.
• Now look at the gamma chart below. Sit as far as possible from the monitor and squint so the lines blur together.


Gamma chart

• Adjust the gamma on your computer so the shade of grey completely across the gamma column is the same at 2.2.
• The monitor is now calibrated.

References

• http://www.normankoren.com/makingfineprints1A.html
• http://www.johncon.com/john/gamma/