What is RGB? Learning how we define, and create, colors digitally

We recently created a fun RGB kids piano that kids can use to learn about color mixing. Working on that quick circuits project might have raised a few questions about RGB, like what is RGB? And why do we have RGB?

In this article we will tackle some common questions about color spaces and learn why, and how, they got their names.

Be sure to check out our hands on RGB color piano activity to further your learning!

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What does RGB stand for?

RGB stands for Red, Green, Blue, or the three colors that are the base colors for this color space. They are the fundamental pieces you can build with. If you want a different color, orange, for example, you will need to mix a certain amount of red with a certain amount of green. 

Imagine if you only had three flashlights, red, green, and blue. If you were to play and mix these lights in any ratio you wanted you could build up a ton of different colors from red, green, and blue. That is why we call it a color space because you can make up more than just those three colors.

What is the difference between RGB and CMYK?

RGB and CMYK are different in the types of paint pots you start with. Remember before we only had red, green, and blue flashlights? In CMYK you don’t have any of those colors to mix. Instead, you have cyan, magenta, yellow, and black. The K stands for black so we don’t confuse it with B for blue!

Instead of mixing flashlights, in CMYK we are mixing pots of paint. So you can take your four paint pots and mix them in a ton of different amounts. Each different amount will give you a new color in your color space. You can make an entire rainbow of colors using either RGB or CMYK color space. Did you notice that the mix of RGB in the very simple color wheel above gave you CMYK, and mixing CMYK in the color wheel on the right gives you RGB? They are all related!

How did they come up with RGB?

While you may think that RGB was invented by artists mixing their paints, it was actually invented by a photographer taking color photos. Painter’s paints are based on pigments we find in nature. While we can recreate those pigments in RGB, painters can just go buy a tube of whatever color they want. 

In photography, however, we can’t do that. To make color photos we actually use filers that filter out the red, green, or blue light. Even on your digital camera, we do this. For each pixel, we see there are really three pixels on the CCD packed close together with red, green, and blue filters counting up how many photons of each color light hits that part of the sensor.

Photographer J.C. Maxwell pioneered this with the worlds first color photograph using RGB filters shown here. To do this he took three separate photographic plates and combined them.

What are other common color formats?

Honestly, RGB and CMYK are the two main color spaces. If you open up a window to look at changing your font color in Microsoft Word you will likely see the option to input a color in RGB, CMYK, or another format called HEX. HEX is not a color space, but instead a computer code for an RGB color. The HEX code will tell the computer how much red, green, or blue to put in and can easily be transferred from program to program.

Can I make black from RGB?

Yes! You can make black from RGB by adding nothing. Remember, RGB is a color space you get from looking at a light source. If we add all the colors together we get white light. If we add nothing, then there is no light and thus it looks black. 

The opposite is true for CMYK. If you lay down no ink then you have white. If you lay down all colors of the ink you get black. This is because CMYK color space is reflective, that is, it is light that hits the paper and then either gets absorbed by the inks in the paper or reflected into your eyes.


What is the difference between RGB and CMYK? 

RGB is called an additive color space, while CMYK is called subtractive. What does that mean? When we look at RGB we talk about adding colors of light together. The color we see is the total sum of all the light we see. 

CMYK, on the other hand, is about light reflected into our eyes, say off a piece of paper. That is why printers use CMYK. We can try to recreate the colors we would see from a bunch of flashlights with the pots of paint, and for the most part, we can do a good job, but it isn’t perfect since there is a difference between shining light into our eyes and reflecting light off a paper into our eyes. 

You might surmise that RGB color space is then always a little lighter, since it is light going directly into your eyes, and you would be right. On the left is a comparison of RGB light and how it would print in CMYK space.

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