Gamma Test

How to read it

1. Set browser zoom to 100%. The stripes are one screen pixel each, and zoom spoils them.
2. Open full screen and sit back, or squint, so the fine lines blur into an even gray.
3. In Gamma, find the column where the solid patch almost disappears into its stripes. The number below it is your gamma.
4. In Gamma scale, find where the edge between the striped top and the solid bottom vanishes, and read the scale below it.
5. Switch the channel to red, green and blue. They should all land on about the same value.

If the patch looks lighter than the stripes in every column, your gamma is lower than 1.8 (mid tones too bright). If it looks darker in every column, your gamma is above 2.6 (mid tones too dark).

What gamma is and what to aim for

Screens do not turn pixel values into light in a straight line. Gamma describes the curve. With a higher gamma, mid tones are darker and images look more contrasty; with a lower gamma, mid tones are lighter and images look flat.

• 2.2 is the usual target for computers and the web; the sRGB standard used on the web is close to it.
• 2.4 is common for watching films and TV in a dark room.
• 1.8 was used on older Mac systems and is now rarely a target.

The patterns work because alternating full white and black lines give half the light of full white. The solid patch that matches them is the value your screen turns into that same half brightness, and that value depends on the gamma.

Why the result can be off, and how to change gamma

• Viewing angle. On many laptop screens, gamma changes as you move your head up and down. Look straight on, at the middle of the screen.
• Scaling and zoom. Any resizing of the stripes averages them and ruins the test.
• Color management. Browsers can convert colors for your display profile, and your system can apply a calibration curve. That is usually what you want, but it means the test shows the whole chain, not the panel alone.
• Not a perfect curve. sRGB is not an exact power curve, and screens vary across the range, so treat the result as an estimate.

To change it, look for a Gamma setting in the monitor menu (often 1.8, 2.0, 2.2, 2.4 or 2.6) or in your graphics driver settings. For an exact result, calibrate with a hardware colorimeter.