Why should you calibrate your monitor?

Every monitor has a number of ways to display a picture. It can be dark or light, tinted in blue or red or any other colour, but only one way is the intended way of the author of a picture. Calibrating your monitor is a way to adjust your monitor to a common standard. If you (the photographer) processed your picture on a calibrated monitor, you can be sure that any viewer with a calibrated monitor sees the picture as you saw it.

(For further reading I recommend the writings of Norman Koren at http://www.normankoren.com/makingfineprints1A.html . He goes really indepth into calibration. I will just stay on the surface of a simple howto.)

You can buy hardware to calibrate your monitor. It’s a small digital camera with suction feet. You fix it on certain places on the screen and run the software. The camera feeds the colour of the screen back to the program which adjusts the settings accordingly. The cheaper ones (below 500€/$) work only under Windows or MacOS. I am using Linux, so I can’t say any more about them.

You can calibrate your monitor without extra hardware, if you replace the digital camera with your eyes and a little more time. You have to adjust three settings, colour temperature, black and white point and gamma.

White isn’t white on your monitor. Somewhere in the menus you can adjust it to a colour temperature between 5000 and 9000 K. Choose 6500 K or sRGB.

The black point is the colour in which your monitor displays pure black. Due to technical reasons it is not really black. You adjust the black point with the black level adjustment of your monitor. From the heritage of the TV set it is labeled “brightness“.

The white point is the the colour in which your monitor displays pure white. This is controlled with the equally mislabeled “contrast“ adjustment.

Gamma covers the display of the mid tones. Here you adjust how light light gray is and how much contrast you see. The standard is 2.2. The name Gamma comes from the mathematical function which describes the voltages of the monitor signal in relation to the level of brightness. Not enough? Try Norman Koren or Wikipedia.

Your monitor should be running (at 6500K or sRGB) for at least half an hour. Open a text editor or some other great empty white space. Push your contrast adjustment up, until you see pure white. I ended at 100%, but compared to the white of bleached paper it is still a bit dim.

Go to the site of Norman Koren ( http://www.normankoren.com/makingfineprints1A.html#Gammabox ) and look at the picture http://www.normankoren.com/Gamma_black_new.png . You see three vertical stripes. Look at the middle one. labeled “A“. Now adjust your brightness so that you see continous black on the upper part and dark gray fields next to the “2.2“ mark. It should be uniformly dark above the 1.9 mark. Don’t fine tune now, as you will come back here!

Start a program for gamma adjustment.

I have heard rumors about Adobe Gamma FIXME

There must be something! FIXME

Get Monica from http://www.pcbypaul.com/software/monica.html or use xgamma in a console without graphical interface. (In the current version of Monica is a small bug: the rulers for green and blue are switched.)

Look at the striped image on Norman Koren website from a distance. You should be so far away that you can not see the fine pattern in the left stripe. Now fiddle with the (locked together) rulers until you see a uniform area around the 2.2 mark. If you see a colour cast you have to unlock the rulers and adjust the individual colours.

Check the black level. It has moved! Adjust it and check Gamma. It has moved! Adjust it and check the black ...... and so on until both are right.

I don’t know how it is done in Windows or MacOS

In Linux you can note the values and insert them in the monitor section of your X configuration file in the form of “Gamma 1.05 1.15 1.136“. More flexible is the use of the commmand line tool xgamma. I made a small script which I start before serious graphical work. I have softer gamma settings ( and a script ) for working with a text processor. The script is:

#!/bin/sh
xgamma -rgamma 1.19 -ggamma 1.05 -bgamma 1.33

I have the striped image of Norman Koren on my hard disk and check it from time to time. My monitor, my eyes and the light in my room are not always the same. But fine tuning is a lot less hassle than the stuff we just did.