Screens

The screen is also a variable

Every pixel you paint is stored as a number. What you see is that number converted to light by a piece of hardware that has its own spectral output, its own white point, and its own gamma response curve. Those properties are not fixed: they change with temperature, with age, and with ambient light. The display is not a neutral window; it is an instrument, and like any instrument it needs to be characterised before its readings mean anything.

The CIE 1931 colour space gave the industry a device-independent language for this: a coordinate system built from experiments on human observers, published by the Commission internationale de l'éclairage in 1931, that lets you describe what a colour looks like rather than what voltage produced it. From that foundation came ICC profiles — files maintained by the International Color Consortium that record a device's measured relationship to the CIE model, so the operating system can map numbers correctly from one device to another. Without a profile, the same file looks different on every screen.

Gamma is the non-linearity between encoded value and emitted luminance. CRT screens responded to voltage with a natural power curve close to exponent 2.2, and the encoding standards written around them — including sRGB, formalised by the IEC as IEC 61966-2-1 — baked that curve in deliberately. Modern LCD and OLED panels have to mimic the same relationship in firmware, because decades of content were encoded to it. The curve is a historical artefact that the entire pipeline still honours.

Gamut — the set of colours a device can actually produce — varies by panel technology and backlight spectrum. Wide-gamut displays can reach well beyond sRGB into the DCI-P3 volume and beyond, which means unmanaged colour pipelines clip or shift hues that the screen could otherwise render. The practical consequence: a saturated red you paint in an sRGB workspace may look correct on a standard monitor and violent on a wide-gamut one if no colour management is applied.

Drift is the quiet problem. A display that was correctly profiled six months ago is not correctly profiled now. Phosphors age, backlights shift, and the LUT loaded into the GPU from an old profile silently misrepresents the hardware. Periodic remeasurement — with a spectrophotometer or colorimeter against a known patch set — is the only remedy. The screen is always measuring; the question is whether you are measuring it back.

What you see is that number converted to light by a piece of hardware that has its own spectral output, its own white point, and its own gamma response curve.