Color Gamut: Understanding Rec.709, DCI-P3, and Rec.2020

One of the most vital elements when looking for a projector is its ability to represent colors. But with projector specs listing various types of color gamuts, which specific color gamut represents the best choice for the consumer? For current projectors on the market there are three main color gamut standards used: Rec.709 (also known as BT.709), DCI-P3, and Rec.2020 (also known as BT.2020). Though there are major overlaps between these color gamuts, each one still stakes out a distinct area within the visible color space. This article will help define these commonly used color gamuts as well as recap what a color gamut means, including why the concept is important for projectors.

By definition color gamut is the range of colors within the visible color space (i.e. all the colors visible to the human eye) which a device such as a projector or display is able to reproduce. You can think of color gamut as the palette of colors from which you can choose to create an image: the wider the range of colors that the palette includes, the richer the images you can create and vice versa. For devices such as projectors and displays the reason color gamut is relevant is because technology has not advanced to a degree in which all the colors visible to the human eye can be represented, thus color gamut is used to express the portion of the overall visible color space which the device can reproduce. It thereby helps define the limits of that device’s color representation.

Many times, when describing color gamut a CIE chromaticity diagram is used, wherein a triangle representing the color gamut is drawn inside the visible color space, represented by a horseshoe-like shape. In such diagrams the bottom-left corner of the triangle represents the “bluest blue” that the given color gamut can display, the bottom right corner is meant to represent the “reddest red”, the top corner represents the “greenest green”, and the area encapsulated by these points encompasses the entire color gamut; in other words all the colors that the device can reproduce.

But beyond defining the range of colors a device can reproduce, the other main reason why color gamut is important is because for devices that depict colors, a color gamut acts as a shared language for every element involved in their ecosystem -- from cameras to media players to the display devices -- to ensure that all the colors used by a given device are in sync with the colors from all the other devices. Without a shared color gamut there would be no way to make sure that a given color produced by a projector, say a certain purple, is the same purple transmitted by the media player. The color gamut therefore acts as a point of reference that defines each color used in the ecosystem which leads to the reproduced image.

As described above color gamut acts as a language for which to define colors, and like languages there are many different types. To ensure that players in the industry are using the same “languages” to define colors, industry groups such as the International Telecommunications Unition Radiocommunication Sector (ITU-R) every so often defines given color gamuts for use by their peers. The discussion below will describe the three main color gamut standards: Rec.709, DCI-P3, and Rec.2020.

Rec.709 is a specification standard released by the ITU-R which includes a unique color gamut as part of their wider “list” of specifications. Though strictly speaking Rec.709 is a set of specifications that covers items beyond color gamut, it’s common to be mainly referring to its color gamut when using the term “Rec.709”. In terms of specifics Rec.709 was released in 1990 with a color gamut geared to help define colors for the now dominant high definition television market.

DCI-P3 on the other hand is a color standard defined by the Digital Cinema Initiatives (DCI) organization in 2010. As can be deduced by the organization’s name, DCI-P3 is the color gamut most commonly used by the film industry, particularly for their digital movie projectors. Beyond the film industry DCI-P3 is also a color gamut utilized by companies such as Apple, Samsung, Google, and others in the mobile device sector.