Index Color (Stochastic) Screen Printing
The content of this article is an excerpt from the ASPA training course The Secrets of Printing T-Shirts and How to Make Big Money!
Index color printing, also known as stochastic, diffusion dither, or FM printing is yet another way to achieve full color printed images on both white, light, and dark colored shirts.
The concept behind index printing is that any image can be reduced to a finite number of ink colors in a color palette. This can be done by sampling the most important individual colors of an image in a graphics program like Adobe Photoshop and choosing the best colors that are representative of that image and creating a limited color table.
The great thing about index color is that you are using "square dots" which do not overlap each other as in halftone printing, as the "dots" align side by side.
Moreover, "square dots" being individual bitmap pixels are easy to output through any printer without the need for a RIP or Postscript capabilities. Index color printing can often produce results equal to simulated process printing, depending on the image and is easy to screen print.
For an excellent step-by-step tutorial on creating index separations visit: http://www.teedesign.com/Technical_Info/Screen_Printing/Index_Separation.htm
Another good source of information on index printing can be found at this site http://www.squaredot.com/.
Featured on this site is information on the program Screenprint Separator. An index printing solution created by David Cran. Squaredot.com offers a wealth of information on the index printing process and will be very useful for anyone interested in index printing.