The Basics

RGB

RGB is about light in the darkness. No light: no color. By controlling the ratio of Red, Green, and Blue, we can create any color we want! Where both red and green light overlap, we get yellow. Green and blue combine to make cyan. Magenta is the total of red and blue. All three make white.

It’s often useful to note which color is absent or lacking. For example, cyan is the absence of red. Or if an image looks too magenta, we add a bit of green.

It gets tricky when we try to express how much of each we want. With most software, we use numbers between 0 (no light) and 255 (the maximum). The RGB value of 0 0 0 is black—all lights out. However, maximum red (255R) on one device may not be as intensely red as on another. That is, 255R will be a different color on different devices; maybe like Santa’s suit on one and more neon on another. After all, any device can produce only so great a range of brightness or saturation. We call that range the gamut and it’s described by its own color space.

In software, we usually choose a standard reference, an often idealized virtual device’s color space. Examples of this are sRGB, Adobe RGB, and ProPhoto RGB. The sRGB color space closely approximates the colors produced by average PC displays—nothing too vibrant. Adobe RGB is a larger color space and can produce more intense colors. Thus, a way to consistently refer to the same perceived color is to give RGB numbers with reference to their color space. For example, 255R in sRGB and 216R in Adobe RGB refer to the same perceived red.

CMYK

CMYK is about dots of ink on paper. Without ink, there’s only paper. By controlling the ratio of Cyan, Magenta, and Yellow ink, we can make many colors. We measure the amount of each from 0% (none) to 100% (the full amount). For practical reasons, we need blacK, too. Thus, CMYK is known as the four-color process.

Each ink absorbs a different color of light. Cyan absorbs red light, for example. All three inks should absorb all light, and thus appear black. However, this may be too much ink for many papers, or could appear as dark brown instead of black. This is why we need black ink.

Some printers use toner and some use ink. Each ink-maker’s inks are different. Paper also affects color, of course. Every device is different. So, as with RGB, CMYK devices also have color spaces, or ranges of color they can produce. That means that the recipe (or build) for any perceived color will vary from paper to paper, and from printer to printer. No single CMYK build looks the same on all printers.

As with RGB devices, there are standard CMYK color spaces that approximate certain press conditions, three of which are SNAP, GRACoL, and SWOP. When we submit files for printing, we’ll often be asked to submit them in a CMYK color space that conforms to one of those standards. This chapter lays out how to do that.

We usually don’t need to know or care what a color’s build is; we typically care only about how it looks. However, there’s a notable exception. If text at small sizes or delicate line-work is printed with more than one ink, we risk misregistration (misalignment of the colors), and thus illegibility. So for maximum contrast and legibility, text is most often printed with black ink only: 0 0 0 100%K. It will look different on different substrates, but it will be sharp. Text color is often the only swatch for which I specify a CMYK build at all!

Process vs. Spot (Solid)

Spot Color

This is a custom color made by mixing different colors to attain the desired one, much like housepaint is made. This is used when a critical match is required and is unattainable with process color printing. It’s also handy when you are printing with few inks to save money rather than with the four inks of process color.

Process Color

This is when various-sized dots of Cyan, Magenta, Yellow, and blacK are set at angles to each other. When small enough, we don’t see them individually, but we see an overall result. Look at an image in this book with a magnifier and you’ll see its dots!