The difference between RGB and CMYK color
Color may be the most important part of your printing project. So it will assuredly cause the biggest headaches. You just spent a lot of time and effort picking out the perfect blue on your computer, but when you print it comes out closer to purple. You have tried a number of different printers with the same result. Why is this happening?
This happens because of how we make color, or more specifically the different ways our computers, and printers make color. Color is made one of two ways, by using light(computer) called RGB color, or ink(printer), called CMYK color. Trying to get these two to match is where problems arise.
The RGB (Red, Green, Blue) color model is made by using light. Think of it like putting light through a prism, you get to see all the colors of the rainbow. Our computer monitors and TV screens use light to create images, so they use the RGB model to make colors. This is also called “additive” because you add various intensities of each primary color to create all the other colors. Each primary color has 256 levels of intensity ranging from 0(no color) to 255(full intensity). Add that all up and there are roughly 16.7 million different colors that can be made with RGB, or in other words, the entire visible spectrum of light.
If you look at the illustration above, the center of the RGB model is white. If you mix all the colors in the RGB model together evenly you get white. This is because you are making the colors with light. It is like you went through the prism in reverse, you mix all the colors back together to make white light. If you want to make black, you don’t mix colors together, you just turn them all off, shut off the light. The screens on your computer and TV are black when you turn them off because the light that produces color has been turned off. In the RGB model black is not a color, it is the absence of color/light.
CMYK “4 color” “Subtractive”
The CMYK (Cyan, Magenta, Yellow, Black) model is used by printers not because they like to be different, but because they need to print colors on paper, to do that you need ink. Unlike light, ink is “subtractive,” meaning it eliminates the other colors so that only the one you want can be seen. For instance, if you want to print green you mix your primary colors together to make green ink. This ink will then only reflect the color green, it subtracts the other colors. Different colors of ink are made by adding the primary colors in percentages. There are not nearly as many variations of ink as there is light. You are limited to roughly 5,000 different colors in the CMYK model. This means there are 16.695 million colors you can make with RGB that you can’t with CMYK. Unfortunately when you pick your favorite color on your computer screen, chances are you won’t be able to print it, at least not exactly(more on that later).
If you look at the illustration above you can see that the center of the CMYK model is black. When you add all the RGB colors together you get white, but when you add all the CMYK colors together you get black. Think about it like this, if you keep adding more light it will keep getting lighter until it becomes white, if you keep adding more ink it will keep getting darker until it eventually becomes black. Now is the time when you say, “Wait I thought the “K” in CMYK stood for black”. Like RGB, CMYK has three primary colors (Cyan, Magenta, and Yellow). In principle if you add all three of these together equally you should get pure black. However, because of impurities in the inks used to make color, black comes out more muddy brown. So printers have added black ink to make CMYK. Not only that, the cost difference of using three inks to make black when you need only one is substantial.
So now what?
To make your life a little simpler you could make sure to only chose colors from the CMYK model (in fact a lot of software already defaults to this), but if you just can’t get over that shade of blue you really like you do have other options. Colors have number codes. With these codes you can start to get an idea of how to make the different color models talk to each other. If the color number for your blue in RGB is, R=0 G=94 B=184, you can then input that into a conversion chart(there are a number of them online). You will typically be given a number of options that you could choose from, (these will be the CMYK colors that are close). Pick the one you like best, take the corresponding CMYK code and input that to get the color you chose. (You will see the largest variations of color in blues and greens.)
CMYK color is by far the most common color model when it comes to printers, but there are others, especially if you are using a commercial printer. CMYK is 4 color (this is what is in your personal printer at home), some commercial printers use 5 color (or more). The extra color that is added in a 5 color model is often referred to as “spot color”. If you need to have a branded color, Coke red for instance, you can add a spot color to make sure it matches exactly. The addition of a fifth color adds thousands of more colors you are able to produce with ink. In fact the fifth color doesn’t even have to be a color, it could be something that adds metallics to the image. The more primary colors you add the more variations of colors you can make. In fact new colors are being made every year (well not new, the color already exists, but now it can be made with ink).
(If you are working on a printing project it is always a good idea to have a sample printed before you mass produce, this ensures the printed image is exactly what you are hoping for.)