The most common type of color separations used in screen printing is spot color separation. Spot color separations are done for vector images. While they are typically solid, spot color separations can include some halftone dots to create a shading effect. Spot color separations are usually created in CorelDRAW or Illustrator.
The four-color process uses halftone dots of CMYK — cyan, magenta, yellow and black — to create detailed, photorealistic images. These types of separations are usually done in Photoshop, and creating a process color separation and printing four-color process correctly can be tricky.
Like traditional four-color process separations, simulated-process color separations make use of halftone dots to create highly detailed or photorealistic images. The difference is that simulated process color separations utilize a range of ink colors. They tend to be more vivid than four-color process prints and can be printed on darker materials, unlike four-color process separations. Like four-color process separations, simulated-process color separations are done in Photoshop.
Index color separations use square pixels of the same size, rather than halftone dots, to create color shading. Performing and printing and index color separation can be easier to perform than process separations. However, it often takes more colors to create a photorealistic print. The separations are performed in Photoshop, but images can be easily transferred from other programs, such as CorelDRAW or Illustrator.