Gamut Excursion Measurements (GEM)—Improving CIE Usage

A common task in color grading is to grade to one gamut while constraining to another. For example, the grade to International Telecommunication Union-Radiocommunication (ITU-R) Recommendation BT.2020 is constrained to DCI-P3. If colorists can quantitatively determine the excursions of colors from the gamut of interest, they can either remap the colors or allow them to clip at the gamut boundary. Currently, this work is handled using a combination of legacy tools and monitoring with reference monitors. This can be time-consuming and prone to errors. The CIE chromaticity chart provides a 2D view of the chromaticity content of the image. This paper presents innovations based on deriving valuable data from the CIE chart that helps colorists quickly determine how far off colors are from the gamut of interest. The Gamut Excursion Measurement (GEM) effectively unrolls the CIE chart and presents a quantitative snapshot of the gamut excursions as a 2D linear chart over the spectrum of colors. The excursions can then be visualized (using GEM) with a multi-level false color heat map. Luminance Qualified CIE is a method of constraining the CIE chart against luminance, allowing users to study colors within specific luminance ranges of interest. Combinations of the above tools provide fast, effective techniques for color grading.