What is monitor gamma?
Gamma is the non-linear relationship between the digital pixel value sent to your display and the actual light it emits. A gamma of 2.2 means a mid-grey pixel value (128/255) emits about 22% of full luminance, not 50%. This curve exists because human vision is itself non-linear — we perceive small luminance changes in dark tones more strongly than in bright tones. Gamma encoding gives us more bit-precision where the eye is most sensitive. The sRGB standard, used by virtually all web content, targets a gamma of 2.2.
Why is 2.2 the standard gamma value?
Gamma 2.2 originated with CRT monitors — the electron-gun voltage to luminance curve happened to be ~2.2, and the entire image pipeline standardised around it. Today it remains the sRGB and Rec. 709 (HDTV) target. Mac OS used to default to 1.8 to match dot-matrix print output but switched to 2.2 with Snow Leopard in 2009. Use 2.4 for dim-room cinema (DCI-P3, Rec. 1886 broadcast). Use 1.8 only for legacy print workflows. For everything else — web, photo editing, gaming — 2.2 is correct.
How do I read the test rows?
Each row shows a fine black-and-white line pattern next to a solid grey patch. The line pattern averages to a true linear 50% luminance (because half the pixels are full white). The solid patch beside it is rendered at the grey value that should look identical on a display with that row's gamma. Step back 50 cm and squint — the line pattern will blur into a flat grey. The row where the blurred lines and the solid patch match is your monitor's actual gamma.
My monitor matches gamma 2.4 instead of 2.2 — is that bad?
Not necessarily. Gamma above 2.2 produces darker midtones and more apparent contrast, which some users prefer for movies in dim rooms. But sRGB content (websites, photos, games) was authored for 2.2 — viewed at 2.4 it looks crushed in the shadows. If you do colour-critical work, recalibrate to 2.2 using the monitor's OSD gamma preset or hardware calibration (X-Rite i1Display, Calibrite). If you only watch movies in the dark, leave it at 2.4. For HDR content, gamma doesn't apply — HDR uses PQ (ST 2084) or HLG curves instead.
What if no row matches — every patch is too light or too dark?
Several causes. First, brightness too high washes out shadow detail and shifts perceived gamma down; aim for around 120 cd/m² (120 nits) in a normal room. Second, contrast set incorrectly clips white. Third, viewing angle: TN and VA panels have strong gamma shift off-axis — sit centred. Fourth, your monitor's gamma preset may be set to 'Off' or 'Native' (uncorrected). Set the OSD gamma preset to 2.2 and recheck. Pair this with /monitor/uniformity (corner-to-corner gamma can drift) and /monitor/banding.
Why does the test require squinting and viewing distance?
The fine line pattern needs to optically blur into a uniform field so your eye sees its average luminance, not the individual lines. At arm's length on a high-DPI display, the lines are too sharp to merge — squinting and stepping back to ~50 cm forces the optical integration. If you wear glasses, leave them on. If you can still distinguish the individual lines from 50 cm, your display is very high resolution — try standing 1 m back. See also /monitor/refresh for motion clarity and /monitor/dead-pixel for panel integrity.