Gamma is the SDR-era transfer function — the formula that translates between the numbers in a regular standard-dynamic-range video file and the actual brightness on the screen. Every HD video, every YouTube upload, every old Blu-ray uses it. Gamma is what made SDR video look "right" on TVs from the 1950s through the 2010s, and it's still the default any modern player assumes unless metadata says otherwise.
Why a curve rather than a straight line? Two reasons, one historical and one perceptual. Historical: old CRT television screens had a built-in physical relationship between voltage and brightness that approximated a power curve of about 2.2 — so video signals were tuned to invert that relationship, producing a final image that looked correct. Perceptual: it turns out human vision is much more sensitive to changes in dark areas than to changes in bright ones, so a gamma curve also happens to allocate more code values to the dark parts of the image where the eye needs them. Two birds, one curve.
The number you'll see is the gamma exponent. 2.2 is the de-facto computer monitor and YouTube standard, 2.4 is the BT.1886 cinema/TV standard for SDR, and very-old systems sometimes used 1.8 or 2.6. The differences are subtle but real — content mastered at gamma 2.4 looks slightly darker on a gamma 2.2 monitor than the colourist intended. In 2026, gamma is purely an SDR concept. HDR formats use entirely different transfer functions (pq, hlg); when content is HDR, gamma doesn't apply.
