Ever So Subtle Participants from China and the Netherlands were asked to choose the less colorful image. Can you tell there’s a difference in brightness? The difference threshold, or just noticeable difference, is the minimum difference between two stimuli noticed 50% of the time.

Qin, S., Ge, S., Yin, H., Xia, J., & Heynderickx, I. Displays, 31, 25-34 (2010)