Defining a Device’s Color Range
If you imagine that the full spectrum of colors visible to the human eye is a vast landscape, a gamut is a specific territory within that landscape. Every device that handles color—from a camera sensor to a computer monitor to a printer—has its own unique gamut. Some devices can reproduce a very wide range of vibrant colors (a wide gamut), while others are limited to a smaller, less saturated range (a narrow gamut).
Visualizing Gamuts
In color science, gamuts are typically visualized as triangles overlaid on the CIE 1931 chromaticity diagram, which is a horseshoe-shaped map of all human-visible colors. The three corners of the triangle represent the most saturated red, green, and blue primaries that the device can produce. All the colors that can be created by mixing these three primaries are located inside the triangle. Any color that falls outside the triangle is considered ‘out of gamut’ for that device and cannot be accurately reproduced.
Key Gamut Standards in Filmmaking
To ensure consistency, the film and television industry relies on several standardized gamuts for content creation and delivery:
- Rec. 709: The long-standing standard for high-definition television (HDTV), Blu-rays, and most web content. It has a relatively small gamut that has been the target for consumer displays for decades.
- DCI-P3: The standard for digital cinema projectors used in movie theaters. Its gamut is 26% larger than Rec. 709, capable of producing deeper, more saturated reds and greens. Most modern consumer devices like smartphones and computer monitors now aim to cover the DCI-P3 gamut.
- Rec. 2020: The standard for Ultra High Definition (UHD) and High Dynamic Range (HDR) content. Its gamut is extremely wide, covering a significantly larger portion of the visible spectrum than DCI-P3. While few current displays can reproduce the full Rec. 2020 gamut, it serves as the target container for modern content, future-proofing it for next-generation display technology.
The Challenge of Gamut Mapping
A primary challenge in post-production is managing the conversion between these different gamuts. When a film graded for the wide DCI-P3 gamut needs to be shown on a Rec. 709 television, a process called ‘gamut mapping’ is required. This process must intelligently compress the out-of-gamut colors from the larger space into the smaller one, aiming to preserve the original creative intent as much as possible without causing colors to ‘clip’ and lose detail.