After last week's post, Amy asked this question:
Ok, I get rgb and cmyk are different color groups or maybe it is settings. What I don't get is why? Is it like pc and mac, the same but way different?
Which is a great introduction to this week's topic.
Last week I explained the concept of color models...RGB, CMYK, etc. Today, we'll look more closely at these two models and why they exist.
Additive vs Subtractive Color
The easiest way to begin this is to talk about colors that are projected (think computer monitor or TV) and colors that are printed (think magazines and brochures). One uses additive color and the other uses subtractive color.
Remember I explained that color models give us the language we need to communicate about color? Well, the language we use to describe projected color is different from the language we use to describe printed color. Projected color is additive color while printed color is subtractive color. Why? Read on.
Visible light is a small part of the spectrum and each color of the spectrum has a specific frequency. Adding different colors of light together increases the number of frequencies and the more colors you add the closer it comes to white. No light means no color, or black. Therefore, light is an additive color system and any device that uses light to project color (computer monitors and TV sets) uses this color system.
Got that? An additive system uses the addition of colors to achieve white. Think of it as painting with light and colors are formed by "mixing" the light. If you mix them all together you get white. The absence of light yields black. Makes sense, right? Let's move on.
The color you see printed on paper uses a subtractive color system. This is the color system we've been familiar with since childhood. It's the color system we use when we paint or use markers or crayons and it works exactly the opposite of the additive system.
Remember how I explained how we see color on objects? When light hits an object part of the spectrum is absorbed. The rest is reflected off of an object and those are the colors we see. Let's use printing ink as an example.
Ink absorbs some of the parts of the light spectrum. The colors we see are the parts of the spectrum that are not absorbed but are reflected off the surface of the inked paper. Mixing inks makes a darker color because more light is absorbed. It logically follows, therefore, that by removing or "subtracting" color you reach a point of zero ink. Instead of black, as in the additive or light method, zero ink yields nothing or "white" in the subtractive color system.
So, here's an easy way to remember them. Zero color in a projected (additive) system means no light or blackness. Zero color in a printed (subtractive) system means no color or white.
Okay, I promise that's the end of the technical discussion of color. But I thought it was important to explain in case you run into these terms again. Now we can move on to RGB and CMYK...which will be easy to understand now that you've got additive and subtractive under your belt.
RGB Color Model
RGB stands for red, green and blue...the three colors that are used to create images on a computer monitor. RGB uses the additive color system. We all learned in grade school that red, yellow and blue are the primary colors which, when mixed, create all the other perceived colors. Well, that's exactly what happens in an RGB system, except the three "primary" colors used are red, green and blue.
We know that if we mix equal parts of red and green paint we'll get yellow, right? And if we adjust the percentages of either primary color, we'll get differing results. The same is true for RGB. An RGB "formula" looks something like this:
R:255, G:255, B:0
This happens to be the formula for yellow...equal parts red and green. But what does the 255 mean? Well, here's the short answer. (Remember, I promised not to discuss anything else technical.)
Let me see if I can make this simple. There are 256 possible color values for every pixel on a monitor. Values are assigned decimal numbers beginning with 0 and ending with 255. So, the absence of red would mean 0 red. 33% red would mean 85, 50% red would mean 127, etc. Don't ask me why they made this so complex! It just is.
Anyway, the same holds true for the other two primary colors, blue and green. Mixing these three colors and adjusting their percentages yields all the colors you see on your monitor. 0% (RGB:0) of each color yields black and 100% (RGB:255) of each color yields white.
Here's a very hastily put together diagram illustrating the RGB color model.
And that, in a nutshell, explains RGB formulas.
CMYK Color Model
CMYK stands for cyan, magenta, yellow and key (black)...the four colors that make up the standard printing process. CMYK uses the subtractive color system and is used for printing on presses and color computer printers. When the three primary colors of this model are mixed together they produce a muddy black, so black ink (called the key) is added as the fourth color.
Unlike RGB, which uses a decimal numbering system to specify how much of each color to mix, CMYK uses a more intuitive percentage specification.
For example, this blue is a color mix of 75% cyan, 25% magenta, 5% yellow and 0% black.
Commercial printing presses as well as most desktop inkjet printers use a process that combines overlapping dots of cyan, magenta, yellow and black inks to create continuous tone images. A good illustration of this is the Sunday comics page. Sometimes, if you look closely enough or with a magnifier, you can see the individual dots of ink.
You can see a very good illustration of the CMYK printing process at this Wikipedia page. Here's a diagram illustrating the CMYK color model.
At this point you may be asking yourself, "If my desktop photo printer uses CMYK, should I be working with that color model instead of RGB?" The answer is no. Only designers who are preparing images for commercial printing need to worry about CMYK. Your desktop printer's drivers are designed to "transpose" the RGB colors into the correct application of the printer's cyan, magenta, yellow and black inks.
I hope this clarifies some of the mysteries surrounding RGB and CMYK.
Answering Amy's question
So you can see, Amy, that RGB and CMYK are not at all like PC and Mac...the same but different. They are more like different and different. Each model answers a specific need.
later...


















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