Gamut Rings: A New Method of Representing Color Gamut

We have developed “Gamut Rings”*1 as a new method to visualize the three-dimensional (3D) color gamut of a display in a two-dimensional (2D) diagram. The gamut ring framework unwraps the volumetric information and maps it into rings, providing the information needed to describe the ranges of hue, chroma, and lightness.

Conventionally, a display color gamut is represented by a triangular area formed by jointing the chromaticity points of the red, green, and blue (RGB) primary set in a chromaticity diagram (Fig. 1). Although a chromaticity diagram is useful for 2D representations, the color gamut of a display actually needs to be evaluated using a 3D color space that includes the lightness axis (L* in Fig. 2). However, it is not possible to determine the size and shape of the color gamut displayed in a 3D plot without changing the viewpoint.

Gamut rings*2 represent a 3D color gamut solid using a 2D diagram. The gamut solid is cut into pieces at regular intervals of lightness (L*). Each piece is then stretched into a slice of unity lightness; the top surface area of the slice corresponds to the volume of the piece. Gamut rings are formed by placing one slice at the lowest lightness level, followed by positioning the other slices around the bottom slice consecutively. The polar angle represents the hue angle of the color gamut.

Whereas Figure 1 shows Display A as having a larger area than Display B, the gamut rings for Display B is larger than those for Display A, as shown in Fig. 3. On Display A, we observe that the colors are darkened, such that the higher relative white causes the white stripes to pop out. This is clarified by the smaller outer rings of Display A. Thus, gamut rings make it possible to evaluate the color gamut of a display more accurately.

The International Electrotechnical Commission (IEC)*3, International Committee for Display Metrology (ICDM)*4 *5, and International Commission on Illumination (CIE)*6 adopted the gamut ring framework as an international standard in January, July, and November 2021, respectively. Gamut rings can potentially be applied in the design and evaluation of color reproduction devices, such as displays and printers, and can be used to conduct performance comparisons for both professional and consumer uses.

Screenshot of “Gamut Rings Viewer” app
Figure 1: Chromaticity coordinates of RGB primary sets for two displays
Figure 2: Color volume of Display A
Figure 3: Gamut rings for Display A and Display B with their sample images

Addendum

Animated explanation—gamut rings rendered from 3D color gamut solid

  1. K. Masaoka, F. Jiang, M. D. Fairchild, and R. L. Heckaman, “Analysis of Color Volume of Multi-Chromatic Displays Using Gamut Rings,” Journal of Society for Information Display 28(3), 273‒286, 2020
    https://doi.org/10.1002/jsid.852
  2. Since the resulting visual appearance resembles the annual growth rings of a tree trunk, such representations are referred to as rings.
  3. IEC 62977-2-1:2021 Electronic Displays – Part 2-1: Measurements of Optical Characteristics – Fundamental Measurements
  4. SID/ICDM Information Display Measurements Standard, v1.1, 2021
  5. K. Masaoka, “New Color Metrology Content in IDMS v1.1,” Information Display 37(6), 33-37, 2021
    https://doi.org/10.1002/msid.1259
  6. CIE 246:2021 Colour Gamuts for Output Media