Making the CIE Chart Indispensable for Color Grading!

With the advent of Wide Color Gamut (WCG), constraining color grading to a smaller gamut while grading to a larger gamut is a common enough task or problem in post-production. For example, one might set the grade to DCI-P3, while constraining the colors to ITU-R BT.709. During this process, colorists typically need to determine the amount of color excursions outside the gamut of interest and then decide on whether they need to remap the colors or ignore the excursions and allow the colors to clip. Most colorists typically use a combination of traditional tools like waveform monitors, along with reference monitors and work experience to make that determination. The CIE chromaticity chart provides a 2D view of the chromaticity content in the image. So far, the general feeling in the industry is that the CIE chart is complex and difficult to use and therefore it has been mostly confined to textbooks and academic publications. This paper proposes a few innovations [1] that help demystify the CIE chart and enable it to provide instantaneous useful information that can help colorists make quick decisions during the color grading process. The first step involves “linearizing” the CIE chart by effectively unrolling it and creating Gamut Excursion Measurements (GEMs), that provides a quantitative snapshot of the excursions outside a gamut of interest. These excursions can then be visualized using a false color heat map to help make quick determinations regarding the excursions. Adding luminance qualification to the CIE chart helps to additionally constrain the CIE chromaticity visualization to certain luminance ranges of interest. Combinations of these enhancements provide tools to make effective and fast decisions during color grading.

Lakshmanan Gopishankar | Telestream LLC | Beaverton, Oregon, United States