A different RGB

What do computer screens and mosaics have in common? I thought little. This week I learned: a lot.

Maybe you’ve heard of CMYK and RGB color spaces. Sometimes, you will be confronted painfully when the color effect of a picture you saw on a screen does not correspond at all to its printed version. The reason is that there are  different ways to produce colors.

As a child we are primarily confronted with the subtractive color model. The primary colors red, yellow, blue – every child knows – result in more colors when mixed together. If you mix all the result will be a dark brown to black. The term subtractive might seem confusing, because you add colors or, more precisely, colorants.

When a red felt-tip pen is applied to a sheet of paper irradiated with sunlight the blue and green portions of the light get absorbed and thus reflect only the red components. The same goes for the green and blue markers. If these three colorants superimpose each other, almost all the light components of sunlight are absorbed and then create an almost black shade. CMYK is based on this same technique, but uses the slightly different colors Cyan, Magenta, Yellow and Black to create more brilliance and sharpness of the image.

Unlike colorants, lights mix in an additive way. Colors on a screen are created by a special form of additive light mixing, called partitive mixing. The screen surface is covered with tiny dots with a diameter of about 0.2 mm, in which there are phosphors. Usually these dots are red, green and blue and appear after being excited by electron beams, that is, after they have absorbed energy.

Green and Red would be hardly mixed while painting, because then you’d receive Brown. In additive color mixing these two colors would result in Yellow, though. Might sound funny, but that is how it works.

Translated into mosaic that means that if you combine red and green tesserae in about the same amount on a surface, that surface will appear yellow. But only if you look at the area from a distance. Because only with increasing blur the human eye mixes the colors.

To understand the possibilities of the RGB color model, we have made interesting exercises during the disegno lessons this week. I will look more precisely at the next mosaics I encounter. And am eager to practice.

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