Gamma 2.2

MAC and PC users should calibrate their monitor Gamma 2.2

Until OSX 10.6 Macs have had a default gamma of 1.8 causing many people to incorrectly calibrate their monitors to gamma 1.8. Apple have now corrected the issue by making the default gamma of OSX 10.6 the same as the long standing PC standard of gamma 2.2.

Why Gamma 1.8 is Wrong

Before the days of colour management it was common to try to match the characteristics of a monitor to the output process. Back in 1985 Apple released their relatively inexpensive LaserWriter printer. It was determined that if the CRT monitors available at the time had their gamma changed from their native level of around 2.5 to around 1.8, then an image that looked about right on screen would look about right when printed on the LaserWriter. The LaserWriter was discontinued in 1988!

Why Gamma 2.2 is Correct

Today, provided you view images in a colour managed application, the application will adjust the image gamma on the fly in order to correctly render it. So you might be forgiven for thinking that setting a display gamma is a mute point. However the gamma you choose effects the performance of your display. For example how smoothly it can render gradients.

Virtually all computer video cards are 8 bit, offering 256 tonal levels for each colour channel. It is mathematically the case that a gamma of 2.2 offers the least relative variation in tonal steps compared to other gammas between 1 and 2.1.

Industry experts since at least 1953 (advent of the NTSC standard) have agreed that for the 'typical' viewing condition on a typical display gamma 2.2 seems to give perceptually the right relationship between tones. Indeed the modern sRGB standard was based approximately on gamma 2.2. Adobe RGB 1998, which is the de facto industry standard for graphic art also has a gamma of 2.2.

Monitor manufactures are well aware of these facts and build their monitors with this specification in mind. So by calibrating your monitor to 2.2 you are likely to minimise the amount of adjustment the video card has to make in order to achieve accurate colour. In turn this means you are minimising the likelihood of banding between tones (particularly evident when you view gradients on screen).

Another advantage of gamma 2.2 is when viewing images on the internet. Many browsers are not colour managed and most images on the internet have been published in the sRGB colour space. With a monitor gamma of 2.2 the image will be at least tonally correct even if the colours are off slightly.

Gamma tuning

Not all monitors leave the factory with a native gamma of exactly 2.2 and for the perfectionists amongst us it is possible to argue that tuning the gamma to say 2.1 or 2.3 might make for slightly better tonal gradients. For this reason gamma 2.2 is not written in stone but the argument for it as your starting point is compelling.