Rec.2020, DCI-P3 and projector colour gamut

Seeing the three gamuts

Rec.2020 has much more extreme green and red primaries than P3 or Rec.709. DCI-P3 significantly expands on Rec.709 and has become the practical creative target for a large amount of modern cinema/HDR material. Rec.2020 is the larger UHD/HDR framework and is much harder for a projector to reproduce in full.

Rec.709: the SDR home-video reference

Rec.709 defines the colour primaries traditionally used for HDTV and Blu-ray SDR. A well-calibrated projector should reproduce this gamut accurately rather than simply stretching it into a wider native gamut. Saturated colours should be correct, not merely more intense.

DCI-P3 and P3-D65

DCI-P3 originated in digital cinema. Cinema DCI-P3 and the P3-D65 form commonly discussed in consumer HDR share the same RGB primaries but use different white-point conventions. In home cinema, people often say "P3" as shorthand for how much of the modern cinema gamut the display can reproduce.

Many UHD titles are encoded in a BT.2020 container while the creative colour content remains largely inside P3. That is why excellent P3 coverage is still a highly meaningful target.

Rec.2020 / BT.2020

Rec.2020 defines much wider primaries and is used as the colour container/signalling framework for UHD HDR. Reproducing 100% of its chromaticity area is difficult. RGB-laser cinema projectors such as Barco Freya+ and Nerthus can approach or claim full Rec.2020 coverage in xy coordinates because the laser primaries can be placed much closer to the Rec.2020 primary locations.

A projector that accepts BT.2020 is not necessarily a projector that reproduces BT.2020. Input compatibility and display gamut are separate specifications.

Gamut area is not colour volume

A 2D gamut triangle tells you which chromaticities are reachable, but HDR colour exists at different brightness levels. Colour volume adds luminance to the picture. A projector may reach a saturated red at low brightness but struggle to maintain the same saturation at higher luminance.

When a manufacturer quotes a percentage, also ask how it was measured: xy area, uv area and three-dimensional volume percentages are not interchangeable.

Why RGB laser is important

Laser-phosphor projectors usually create some colours from a broader phosphor spectrum. Many can reach P3 with filters or careful light-engine design, but a colour filter can cost brightness. RGB laser uses dedicated red, green and blue laser primaries, making extremely wide gamut possible without the same filter strategy.

RGB laser can also introduce other engineering considerations such as speckle, safety classification and optical complexity, so wide gamut is one part of the complete projector design.

Accuracy before size

A smaller, accurate gamut is preferable to a larger gamut with incorrect hue, saturation or grayscale tracking. The goal is for the system to map Rec.709, P3 and BT.2020-container material correctly for the projector's measured capability. This is where a 3D LUT in a madVR Envy or Lumagen Radiance Pro can become valuable in a reference system.