CMYK and RGB

CMYK stands for cyan, magenta, yellow, and key (black). This color model is primarily used in the printing industry. CMYK uses a subtractive color method, where each color is printed in a layer on top of each other to create the final image. A full-color image is produced by mixing the four primary colors in different percentages to create different colors. CMYK is often used for printed materials such as brochures, catalogs, and magazines.

RGB stands for red, green, and blue. This color model is used in the digital industry. RGB uses an additive color method, where the primary colors are combined to create different colors. In RGB, full-color images are produced by mixing the three primary colors in different percentages to create a broader spectrum of colors. RGB is often used for digital displays such as computer monitors, televisions, and mobile devices.

It is important to note that when designing for print, it's essential to convert RGB images to CMYK to achieve accurate and predictable color reproduction. Conversely, when designing for digital displays, RGB is the color model of choice.

Then a question, why we can’t use RGB for book printing?

The offset press only have 3 ink, which are cyan, magenta, yellow, and key (black). if you use RGB, the only way is convert to CMYK, and the color will be a bit different for some pictures, normally the RGB changing to CMYK color will not be much different.

RGB has 16 million colors while CMYK has only 1 million colors which is a theoretical value and in practice it is even less due to process limitations. Therefore, if you use RGB colors to design your artwork and intend to print it, it is highly likely that the colors will be off because some colors in RGB simply cannot be matched with CMYK ink. This means that there will be a significant difference in the color of your printed materials compared to how they appear on your computer monitor.

CMYK, also known as the printing color mode, is specifically designed for printing purposes. It differs from RGB in a significant way: RGB is an emissive color mode, which means that you can see the colors on your screen even in a dark room. CMYK, on the other hand, is a reflective color mode that relies on external light sources to reflect off the printed surface and into our eyes for us to see the colors. If there's no external light source, like in a dark room, we won't be able to see the colors on a printed piece.

Images displayed on screens are in RGB mode, while those printed on materials like magazines, newspapers, brochures, etc., are in CMYK mode. It's important to note that RGB and CMYK are closely related - you can think of it this way: RGB includes CMYK, while CMYK doesn't include RGB. This means that if you use an RGB document for printing, you may not get the exact colors you see on your screen