Color separation is the process of converting an image, design, or photograph into a set of colors that can be recorded on screens and printed. The separation process of screen printing is a crucial element in developing a great print.
There are several types of color separations. Each is based on the style of the graphic being printed along with other variables such as the number of colors and the color substrate the graphic will be printed on. The complexity of the separation process can range from spot color separations for simple designs to simulated process color separations for high-end photographic designs. Each technique has different behaviors on press:
spot color separations
Spot color separation refers to separate solid colors that do not mix. Spot colors are used to print text, solid lines, and area images, but not full-color photos or designs with complex gradients. Spot color separation is the most basic idea of color separation where each different color block is on its own board/screen.
Simulated Process Separations
Simulated process separation is the most widely used type of separation for printing photorealistic images and T-shirt designs that contain millions of colors. This process uses elliptical halftones that overlap at the same printing angles. This parting approach works for almost all designs on shirts of any color.
Index color separations
Index separation is a separation method that converts images using equal-sized stochastic square dots instead of elliptical halftones. The end result is a bitmap image in which each square pixel represents a different color in the limited color palette. The square dots sit next to each other without overlapping. Although an index break is not suitable for all layouts, it has many advantages for printers:
- No moire! Stochastic bitmap dots are easily burned to mesh without the possibility of moiré.
- No ink buildup. Since the square dots are placed next to each other like a grid or puzzle, not much ink builds up.
- The appearance of the prints is to be printed on any color substrate: light, dark and bright colors. Shirt color doesn’t affect index breaks the way it can with elliptical dots.
- Less variables in the press. An index separation eliminates many press variables that can arise with other types of separations.
- Since the halftone pattern is a bitmap, no raster image processing (RIP) software is needed to produce movies.
True CMYK process separations
The CMYK process separation mixes 4 main colors (cyan, magenta, yellow, black) to produce a full color image. This technique is commonly used in offset printing. When screen printing with process inks, some colors, such as bright red, purple, and green, are difficult to reproduce and can be generated by additional screens to create a vivid print.
Unlike other separation techniques that use opaque inks, CMYK process inks are light and transparent. For this reason, CMYK separations are usually printed only on white garments. Although CMYK process prints can be reproduced on dark garments using a white base, the simulated process technique on dark garments will achieve a brighter, more uniform print. CMYK separations are printed with elliptical halftones and each screen angle is separated by 30 degrees. Doing this creates a rosette pattern that allows the ink to mix and create a wide color spectrum.
Regardless of the process you choose, make sure your decision is informed by what will work best for the design, the shirt, and your press.