Appendix: Gamut Evaluation Standard & Methods

Overview

In 2019, the ISO released a new standard for evaluating color gamuts:

ISO/TS 18621-11 (First edition 2019-12)
Image quality evaluation methods for printed matter
Part 11: Colour gamut analysis

And we collectively, finally, thankfully, had a standardized method of calculating a gamut surface and the volume of that gamut. There are a few important things to note about these methods:

RGB and CMYK only

The standard does not provide any methods for calculating gamut surfaces or volumes for nColor printing systems (CMYK + additional inks or non-CMYK ink sets). The calculation of an nColor gamut surface can be a very complex process and ColorThink 4 uses our proprietary algorithms for this function. When it comes to calculating the volume of these surfaces, ColorThink 4 uses similar techniques to those in 18621-11.

RGB and CMYK Gamut Volume Calculations are 18621-11 Compliant

Profile volume numbers calculated in ColorAssets and in the ProfileInspector are fully 18621-11 compliant for RGB and CMYK profiles

ISO Gamut Surface calculation methods

We refer you to the 18621-11 standard for full details about how these calculations are performed.

When calculating gamut volume, we adhere to these methods. When calculating a gamut surface to display in ColorThink’s Grapher and the resolution is set to “ISO Spacing”, then the gamut surface is also compliant. When other resolutions are used, we calculate using our proprietary algorithms which allows for better handling of strange channel behavior, printing system calibration, alternate grid resolutions and other fault-tolerant techniques.

While ColorThink augments the techniques defined in 18621-11, we don’t disagree with the methods in the standard. ISO standards are meant to define technology and techniques for as broad a range of applications as possible.