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 screen printing separation process 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 in the 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 plate/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 separation approach works for almost all designs on t-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 gap is not suitable for all layouts, it has many advantages for printers:
- No moire! Stochastic bitmap dots burn easily 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 accumulates.
- The appearance of the prints is to be printed on any colored substrate: light, dark and bright colors. The shirt color does not affect the index separations the way it can with elliptical points.
- 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.
CMYK real 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 generally printed on white garments only. 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 30 degrees apart. Doing this creates a rosette pattern that allows the ink to blend and create a broad spectrum of color.
Regardless of the process you choose, make sure your decision is informed about what will work best for the design, the jersey, and your press.