Color printing, process color and spot color.
Color printing, process color, and spot color printing come into play when designing a book. The book may have color photographs, illustrations, or type in color. An understanding of color on the pages that are printing on press is vital. What you see on your computer screen may not be what you see on the pages of the physical book. Let’s start with the basics; RGB versus CMYK.
Red, Green, and Blue are the colors used in RGB. The color is created from colored light. RGB is not only for monitors, but also any screen that reproduces color for television, movies, mobile phones, tablets, laptops, and digital cameras for color photographs.
RGB has the widest array of color but is not used to reproduce photographs and images that print on press. The images need first to be converted to CMYK to print properly.
Cyan, Magenta, Yellow, and blacK are the four inks that make up CMYK process color printing. Process color book printers usually print on 6-color commercial printing presses in CMYK. Sometimes a spot ink or varnish is added, but the cost is extra. CMYK has its issues because of a more limited color array. The designer fine tunes process color to look great on their monitor. Sometimes when the books are printed the color is off. It is usually the designer or the printer who gets the blame. But that might not be the story at all.
While process color images can be at times difficult to get right on press, these are usually problems with viewing color or not understanding spot versus press color results. Self-publishers and designers may need to better understand what happens on press if it is not a proof or press problem.
Use a loupe, linen tester, or magnifying glass and look at a full-color printed photograph to see the rosette. Screens are reproduced at different angles: Cyan 15 °, Magenta 75 °, Yellow 0 °, and blacK 45 °. This produces a rosette, the process color dot pattern seen on closer magnification of a printed image.
Process color printing
Process color printing uses CMYK, the four inks used on a printing press. As stated previously on the preceding page, it is composed of Cyan, Magenta, Yellow, and blacK. Color photographs are printed in CMYK, never RGB.
Even some mock duotones are printed in process color. Printing is not an exact science, but we can come incredibly close using the right equipment, proofs, and knowledgeable staff.
Getting great color is a process. What we do, and the advice we give varies. Some authors want “pleasing color” which is our standard. Others may need “exact match” which costs more to achieve because of the cost of additional proofs.
“Exact match” means generating press proofs or wet proofs. Since printing is an art, even exact match may not match precisely on every page of every book.
Spot color printing
One ink tray on a press filled with a pre-mixed ink prints a spot color. In addition to knowing what these terms mean, book designers also need to know how to designate color correctly in InDesign. Spot color is one ink added to a tray on a printing press. Sometimes a PMS ink is selected. If only one spot ink is in use on press, images and text will all print in that color.
Two or three spot color inks can certainly be used on press. Usually when more than four spot color inks, it is more cost effective to use process color. The exception is if you have a logo color that does not reproduce well in process color. You need to print that in spot. If you compare the same spot color next to process color inks, the printed result may be quite different.
The Coca-Cola brand has been around since 1886. The beverage manufacturer has their own formula to print Coca-Cola red. If we match this spot ink color exactly and compare it to a process 4-color screenbuild in CMYK, it will not match. This is a perfect example of CMYK having a narrower color array than RGB. The solution for a brand like Coca-Cola, or even a color in a book that does not look the same when viewed in process color, is to use a spot color. That always means adding another ink tray to the press.
Adding inks on press
The Pantone Library is practically indispensable. It can be pricey for new designers. If you can only buy just one swatch book or fan deck, buy the Pantone Color Bridge. The reason is that it has the process color screenbuild (CMYK) and the solid (SPOT) inks side-by-side. It also has the HTML color equivalent.
The Pantone swatch deck may be used to evaluate color choices. Even if you are choosing CMYK colors in InDesign or Photoshop swatches, the best and most cost-effective way to have full control over color is to select screen builds from the Pantone Color Bridge. Adding a fifth color on press costs more. Check with your printer before you set-up your InDesign files.