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CIE chromaticity diagram
(springing) (thudding) - Now let's return to the human eye for a moment. Remember, the human eye is the sensor which light must pass through to be perceived. So we need to understand the limit of the human visual system. In the 1920s, experiments were done to map the color space perceivable by humans. From purple, all the way around the rainbow, to this red, this defines all colors of a single wavelength. These are known as spectral colors, and inside this region, we have all combinations of those pure colors. Scientists plotted the limit of the pure colors we can perceive. Notice it takes this funny looking shape. One reason this shape is useful is something called perceptual uniformity. That's a fancy way of saying that we can find the mixture of two colors, such as this red and this green, by simply looking at the midpoint of them, right here. It's known as the CIE chromaticity diagram. CIE refers to the scientific group that published the findings. Compare this to the hue saturation color wheel, which is not perceptually uniform. Pure red is here, pure green is here, but the middle of these two points is not pure yellow at all, it's a very desaturated yellow. Okay, let's pause here. In this next exercise, we'll challenge you to think more about this CIE chromaticity diagram, and perceptual uniformity.