Let’s say you have three lights, a red and green and a blue with precisely known single wavelengths. 3) 1931 RGB Color Matching FunctionsĬIE 1931 contains 3 functions called the RGB color matching functions. Note: The 1924 V(λ) was eventually shown to under represent our sensitivity at the blue end of the spectrum. Or to put it another way, if you have a green and blue light that appear to be equally bright, then you know that the blue light is more luminous. What this tell us is that two lights, 550nm and 400nm can have the same radiance (an objective unit) but appear to have different brightnesses. Excited yet? 2) 1924 Luminous Efficiency Function, V(λ)īefore the fundamental work of colorimetry occurred CIE published a function, V(λ), that describes the human eye’s sensitivity to light at different wavelengths in daylight. The LCD can combine red and green light in the right amounts to mimic the human cone response of spectral yellow light.ĬIE 1931 is a model that tell us how to create these matches. This is why you can create a color that looks like spectral yellow on a LCD display that has no yellow lights. We can reproduce a color if we can create a spectral distribution of light with the same cone response as the original distribution. It means we don’t need the original light to reproduce an observed color. This phenomenon is called metamerism and it has huge ramifications for color reproduction. Color science started to make a lot more sense when I finally understood this. It turns out every color (or, unique cone output) can be created from many different spectral distributions. You could imagine a leaf and a green car that look the same to you, but physically have different reflectance properties. We see this particular reflected spectral composition as green. The leaf absorbs most wavelengths as heat, but reflects visible light around 550nm. Below is the spectral distribution of a spinach leaf illuminated by sunlight. The sun emits light across many wavelengths and objects around us reflect some wavelengths and absorb some wavelengths. Humans can perceive light with waves as small as ~380nm and as large as ~750nm. Wright Guild Color Matching ExperimentsĪ principal quality of light is its wavelength.1924 Luminous Efficiency Function, V(λ).It does not fully describe the subjective and complicated process of human color vision, it’s not without edge cases, but it is relatively easy to work with. It’s a mathematical generalization of human color vision, that allows us to define, and accurately reproduce colors in most situations. You can think of CIE 1931 like you would Newtonian physics. Color matching allows gives us a basic framework for color reproduction. To reiterate that point, Color Matching Systems are not focused on describing color with qualities like hue or saturation, they just tell us what combinations of light appear to be the same color to most people (they “match”). Color matching does not attempt to describe how colors appear to humans, color matching tells us how to numerically specify a measured color, and then later accurately reproduce that measured color (e.g. Do you see any color prints around you? Are you reading this on a color display? All of that is made possible by CIE 1931.Ĭommission internationale de l’éclairage (CIE) is a 100 year old organization that creates international standards related to light and color.ĬIE 1931 is a Color Matching System. I recommend Jan Koenderink’s Color For the Sciences: īy welcome: blog post is an introduction to the CIE 1931 color system, an international standard model of human color vision that is used all around you. Differentiating theoretical colorimetry from the CIE’s implementation of it will be a milestone in your understanding.It’s the modern standard but the theoretical work was done by James Maxwell in the 1850s. CIE colorimetry isn’t the whole story of colorimetry.Colorimetry is essentially linear algebra, human perception is much more complex. Don’t confuse understanding it with understanding color perception. CIE colorimetry isn’t even half the story of color science, it’s a tiny piece of the huge puzzle of human perception and engineering that is color science.Understanding the foundation of CIE colorimetry is very practical but here are some things to remember. I’m older and wiser and I wanted to issue a few disclaimers. Edit 2017: This was the first thing I ever wrote about color.
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