Digital representation
What R, G and B actually mean: additive primaries, linear light, transfer functions, code values, matrices and why 255,0,0 without a colour space does not define one specific red.
RGB is a set of three coordinates inside a predefined system. Until the primaries, white point and signal encoding are known, three RGB numbers do not uniquely define the light a display should emit.
Quick reference
R/G/B are contributions of the primaries of a specific system.
Colour space, transfer/encoding and range are required.
Critical for physically meaningful compositing and interpolation.
It is not a fourth colour primary.
The exact red, green and blue are defined by the colour space — these labels are not universal spectral colours.
A display creates colour by adding light from three primaries. Zero in all channels means no contribution from those primaries, while increasing channels adds emitted light. This is fundamentally different from subtractive printing models in which dyes remove parts of the incoming spectrum.
Every RGB system defines the chromaticities of its red, green and blue primaries. Rec.709, Display P3 and Rec.2020 use different coordinates, so R=1, G=0, B=0 describes different reds in those spaces. The letter R names a channel in a system, not one physically fixed shade.
The triplet 255,0,0 only says that the first channel is at its maximum and the other two are zero in a particular encoding. Without the colour space, transfer function, bit depth and range, the description is incomplete. The same hex value can therefore be reproduced physically differently across differently managed systems and displays.
In linear-light RGB, doubling a channel value doubles that primary's contribution to physical light intensity. Many blending, blur, compositing and physically meaningful interpolation operations are correct in linear light. But storing images directly in linear form at limited bit depth is not always efficient.
A transfer function redistributes code values relative to light. Historically this was tied to CRT behaviour; today it also helps use code values efficiently and build a consistent camera → signal → display system. sRGB, BT.709-style camera encoding, gamma 2.4 display response, PQ, HLG and log curves are different things even though interfaces often group them under a Gamma menu.
Floating-point workflows often normalise RGB to 0–1, 8-bit graphics use 0–255, while 10-bit video range normally reserves code values outside nominal black and white. These numbers describe encoding but do not by themselves change the primaries or white point.
If two RGB systems are defined through CIE coordinates and white points, linear RGB can be transformed through matrices, often using XYZ as an intermediate. If the white points differ, chromatic adaptation may be required. If the target gamut is smaller than the source, a matrix alone does not guarantee graceful out-of-gamut behaviour, which is where gamut mapping enters.
In wide scene-referred working spaces, real colours can temporarily acquire negative RGB components or values above nominal 1.0 after transforms. In a floating-point pipeline this can be a valid intermediate state. The problem begins when those values reach a limited display-referred output uncontrolled and clip.
Alpha normally describes transparency or coverage. In premultiplied representation, RGB has already been multiplied by alpha; in straight/unpremultiplied representation it is stored independently. This matters greatly for compositing, but alpha does not expand the colour gamut and is not another primary.
In Resolve, the same pixel can successively exist as camera-space RGB, timeline/working RGB and output/display RGB. The question 'what are the RGB values here?' should therefore always be followed by 'which colour space and gamma is this node using at this point in the pipeline?'
The main practical rule is simple: RGB without context is just numbers. Before any CST, LUT or manual transform, first establish what those numbers mean at the input.
Technical definitions are anchored to standards bodies and primary specifications wherever that distinction matters.
