
Photographic test charts for measuring color accuracy in cameras have historically included a limited number of skin tones, typically in the form of uniform color patches. Such charts are not representative of the wide range of skin tones found in humans, and do not test the behavior of modern automatic exposure, white balance, and focus (3A) algorithms that are commonly driven by facial detection in today’s digital consumer cameras. We built upon our previous work on the development of printed skin tone charts featuring detectable faces by conducting a study with human participants whose skin tones approximately span the Monk Skin Tone Scale. Participants were photographed under a series of controlled lighting conditions, and each scene was then reproduced using a high-resolution inkjet print of the participant. Corresponding captures of the human subjects and the printed charts were quantitatively compared by calculating the CIEDE2000 color difference for regions of interest across the subject’s face in the scene. This analysis evaluates how printed skin tones behave across exposure settings and lighting conditions relative to real skin, with the goal of determining whether printed charts provide a suitable solution for repeatable, lab-based image quality testing in face-present scenes. While not intended to replace final field testing with real human subjects, results indicate that face charts printed with sufficiently wide-gamut printers can provide an effective solution for lab testing and benchmarking of color accuracy and 3A behavior in a controlled and repeatable manner.

Members of several working groups within the ISO Technical Committee 42 (photography) have begun addressing the important topic of providing guidance for which skin tones to use for image quality testing in various photographic applications. For example, when color patches for skin tones are used in TC42 standards, they should be inclusive and represent a broad range of skin types. Skin tones are present in more than 60% of all captured photographs and therefore need to accurately be corrected in digital cameras, properly displayed and printed on various softcopy and hardcopy devices, and the permanence of the printed colors needs to be determined. During the 2023 plenary meeting of TC 42 in Japan, an ad hoc working group (AHG) was initiated to develop such guidance and report back during the upcoming 2025 plenary meeting in Berlin. The group has investigated existing skin tone studies, including Fitzpatrick, Von Luschan, L’Oreal, PERLA, Monk, Pantone ST, Massey NIS, Verkruysse, Holm and Wueller. It is currently drafting an ISO Technical Report that will document the work and result in recommendations regarding the selection of skin tone color patches and spectra to use for ISO related applications.