Colour range
What to do with colours outside a target gamut: clipping, compression, hue preservation, luminance interaction, Rec.2020-to-P3/Rec.709, ACES RGC and Resolve workflow.
A matrix transform can say where a colour should land mathematically, but it cannot guarantee the target display can reproduce it. Gamut mapping solves that mismatch: how to fit unavailable colours without crude hue/detail collapse.
Quick reference
Different source colours can become one target colour.
Soft compression of the outer gamut instead of hard clamping.
GAMUT MAPPING
Camera gamuts and working spaces are intentionally wider than delivery spaces. After camera transforms, saturation operations, VFX and tone rendering, colours can sit outside Rec.709, P3 or a real display gamut. That is not necessarily a source error; the problem appears when such colour must be represented on a smaller target.
A matrix conversion correctly changes coordinates between two linear RGB bases, but out-of-gamut target values become negative or greater than 1. If they are immediately clamped, multiple distinct source colours can collapse to one boundary colour. Mapping adds a nonlinear solution around the gamut boundary.
Channel/gamut clipping truncates whatever does not fit. With saturated LEDs, signage, lasers, neon and CG it can create flat saturated patches, hue skews and lost texture. Clipping may be acceptable as a deliberate hard boundary, but it is too crude for general rendering.
Instead of truncation, the outer region is progressively compressed toward the target boundary. A good compressor leaves the inner gamut mostly unchanged, begins acting near a chosen threshold/knee and preserves saturation ordering: a more saturated source should still look more saturated after mapping.
Reducing RGB channels or saturation in the wrong space can rotate hue substantially, especially near a gamut cusp. Modern gamut-mapping algorithms often work in perceptual/cylindrical representations or use hue-aware boundaries so chroma can be compressed with less change to perceived hue.
A 2D CIE triangle is useful geometry for primaries, but a real display's colour volume contracts at very low/high luminance and depends on technology. HDR gamut mapping is therefore best considered together with tone mapping: a very bright saturated colour can be unavailable even if its chromaticity sits inside the nominal 2D triangle.
BT.2020 defines very wide primaries, while many HDR mastering displays are closer to P3 inside a BT.2020 signal container and SDR delivery is usually Rec.709. Each narrowing step can create out-of-gamut colours. A file tagged Rec.2020 therefore does not mean every pixel lies inside the physical gamut of a particular display.
Scene-referred camera values can become problematic before output rendering, for example extreme camera-native colours after an IDT. Display-referred mapping fits the rendered result to the target. ACES Reference Gamut Compression is an example of scene-referred technical compression; the output transform then performs display rendering.
ACES 1.3 RGC was introduced to handle problematic high-chroma scene values before the output transform and reduce artefacts such as colour inversion/negative values. It is not a creative saturation effect and not a substitute for final display gamut mapping; its stage needs to be understood inside the ACES pipeline.
In managed RCM, the output DRT may already include gamut compression. CST exposes mapping controls for wide-to-narrow transforms. Before enabling another compressor, first determine whether the project output transform is already doing the same job. Then test saturated LEDs, skin near neon, graphics and synthetic gradients; they reveal weak mapping quickly.
Successful mapping is judged by hue continuity, saturation ordering, texture, skin stability and the absence of hard plateaus. A vectorscope helps show direction and extent but does not replace the target display. A numerically in-gamut result can still look worse if the algorithm destroyed local perceptual relationships.
If a wide-gamut source looks fine before the output transform but develops neon clipping or hue shifts afterwards, inspect the boundary/mapping stage and possible stacked compressors rather than reaching first for Saturation.
Technical definitions are anchored to standards bodies and primary specifications wherever that distinction matters.
ITU report dedicated to wide-to-narrow gamut conversion.
ACES gamut-compression architecture and rationale.
BT.2020 colorimetry and HDR system context.
CST/RCM gamut mapping controls and output transforms.
