Getting comfortable with CIE charts for color grading

A common task in color grading in post is to grade to one gamut while constraining to another. Example, grade to ITU-R BT.2020 but constrain to DCI-P3. If colorists can quantitatively determine the excursions of colors from the gamut of interest, they can then 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 chromaticity content of the image. Traditionally, the CIE chart has been a mystery relegated to academic textbooks and used by those with deep knowledge of color science. This paper presents innovations based on deriving useful 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 outside a gamut of interest as a 2D linear chart over the spectrum of colors, thus helping to quickly identify regions of interest to focus on. The excursions can then be visualized (using the GEM data) 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.

Published

2023-10

Content type

Original Research

Keywords

CIE, color grading, false color, gamut boundary, region of interest, luminance qualified, Gamut Excursion Measurement, GEM

DOI

10.5594/M002024

ISBN

978-1-61482-964-5