Equivalent Luminance Test based on Kindlmann, Reinhard, and Creem. https://doi.org/10.1109/VISUAL.2002.1183788

A useful testing vector image for determination of Equivalent Luminance under steady state viewing.

Those interested in testing relations of chromatic samples versus achromatic equivalent luminance.

Testing Equivalent Luminance is a "notoriously" challenging proposition.

“This effect is probably responsible for much of the difficulty for which heterochromatic photometry is notorious... The variation of luminance required for constant brightness when saturation is changed rules out the comparison-with-white method as a source of luminosity data which will follow an additivity law.”

Loci of Constant Hue and Brightness Determined with Various Surrounding Colors, MacAdam, 1950

Any digital content creation app can harness this image.

Heterochromatic brightness matching is challenging for a number of poorly understood reasons. This image uses a notion of perceptual segmentation to differentiate the brightness in a clever manner. The fill region of the supplied SVG can be filled with a chromatic mixture. When placed atop of an adapted achromatic background, the general appearance of the face will be anchored on one side or the other when the Equivalent Luminance diverges. As the sides approach ambiguity, the Equivalent Luminance result is approximated.