What Does a >100% Rec.709 Color Gamut Mean?

In the field of color reproduction, experts use the term color gamut to describe the range of colors within the overall spectrum of visible colors (also known as a color space) that an imaging device – in our case a projector – is able to reproduce; you can think of it as similar to a painter’s palette. As such, a projector with a wider color gamut is by definition able to reproduce more colors in the visible spectrum.

One of the most common methods used to visually represent a color gamut, is with a triangle drawn within the CIE color space diagram, where each corner of the triangle represents the purest red, green, and blue that the device is able to reproduce.

But given that projectors are just one type of device within the larger imaging ecosystem – an ecosystem that includes other devices such as cameras, displays, and so on – defining their color gamuts is not enough to describe their color performance. This is because the manufacturers of each type of device in the ecosystem need to make sure that every color in their devices’ color gamut are defined the same across the board, otherwise, when trying to reproduce the same image, each device would come up with different versions of each color. That’s where the Rec. 709 color gamut comes into play.

With the Rec. 709 standard in hand many brands have found that one of the most convenient ways to characterize their product’s color gamut is as a percentage of the Rec. 709 color gamut. While doing so seemingly helps the consumer quickly understand the degree to which a device can reproduce the Rec. 709 standard’s colors, this kind of description for a color gamut can be easily misinterpreted, particularly when a brand advertises a color gamut that exceeds the Rec. 709 color gamut – such as 125% of Rec. 709. Because by advertising a color gamut with 125% of Rec. 709, the implied – but incorrect – message is that this device’s color gamut not only fully covers the Rec. 709 color gamut but also includes more colors.

The truth is that the claim that a color gamut 125% of Rec. 709 only means that the overall size of the respective product’s color gamut is over 100% the size of the Rec. 709 color gamut, it does not necessarily mean that said color gamut covers 100% of Rec. 709 plus an additional 25%. There can be many instances where 125% of Rec. 709 color gamut covers 90% or less of the Rec. 709 gamut, as seen in the image below.

The proper way of communicating how much of the Rec. 709 standard covered by a color gamut instead is through color coverage.

As mentioned above, a device with a color gamut that exceeds the Rec. 709 standard does not necessarily mean that it is able to reproduce all the colors in the Rec. 709 standard. Color coverage on the other hand better expresses a device’s capability to do so because it actually represents the percentage of overlap between the device’s color gamut and the Rec. 709 standard. So, a device with a color coverage of 95% of Rec. 709 is guaranteed to be able to reproduce 95% of the Rec. 709 color gamut accurately, while a product with over 100% of Rec. 709 might only be able to reproduce 90%.

Furthermore, color gamuts that exceed the size of the Rec. 709 standard but feature a lower than 100% color coverage will actually lead to issues with their color accuracy, including color deviation and oversaturation. This is due to the fact that because Rec. 709 is used as a standard to sync up colors across devices, any device whose color gamut features large chunks outside of the Rec. 709 boundaries – as is the case with devices that have large color gamuts but lower color coverage – will invariably produce colors that deviate from the colors produced by another device that has adopted the Rec. 709 standard. Similarly, oversaturation will also occur when the areas of a large color gamut that lie outside of the Rec. 709 boundaries skew towards a specific color, most commonly red.