Rich black vs. Plain black

Problem

On a computer monitor, there is only one way to represent black. When there is no light coming from the monitor, the screen is black.

In print there are many different ways to represent black. The simplest is "plain black," or 100% black ink (0C, 0M, 0Y, 100K). However, you can also create a "rich black" by printing other inks along with black. There are many different possible ink combinations - the most common "rich black" contains percentages of all 4 inks: 63C, 52M, 51Y 100K. This particular variant owes it's popularity to Adobe Photoshop - when an RGB file is converted to CMYK, areas that are absolute RGB black (R0, G0, B0) will wind up with this combination, unless certain default settings have been changed. Other possible flavors of "rich black" are "Cool Black" (60C, 0M, 0Y, 100K) and "Warm Black" (0C, 60M, 30C, 100K).

No red, green, or blue (rgb) phosphors are glowing.

The problem with all these blacks is that they all look the same on the computer screen - all of them are represented as R0, G0, B0 - but they will not look the same on paper. A classic beginner's mistake is to take a photoshop image that fades into rich black on all sides, place it in a picture box in the page layout software, and assign the picture box a background of "black" ("black" in page layout software = plain black). This appears to be continuous and uniform on the computer screen. If the layout were to be printed, however, there would be a distinct difference between the areas of rich black and plain black.

Image and background look the same Print black look different

For more and solution, see Rich black vs. Plain black