There is a wide variety of separation types and the terms often get misused or misunderstood. The majority of colors separations we do are “simulated process color” where you actually print with standard ink colors that are separated to look like CMYK. These prints are brighter on a shirt and print better and easier than CMYK.
Here are some common separation types:
This is the “bread and butter” of the industry. Spot Color images generally have specific solid colors that can also be comprised of small dots called Halftones. Spot Color separations and prints are generally used for logos, school designs, clipart, hard edged graphics, cartoons or other images that have a Black or dark outline.
A Spot Color image can be as simple one-color design or a complex ten color masterpiece. It can include lots of shading, gradations and detail, yet they still generally have a flat, cartoon-like look and are not photorealistic.
Spot Color separations are done in Vector based programs like CorelDRAW and Adobe Illustrator.
Process Color images comprised of the colors of Cyan , Magenta, Yellow and Black. Process Color prints are generally referred to as CMYK (the “K” is for the “key” color of Black). All magazine photos are printed using only these four colors. If you took a magnifier to the images, you would see small halftone dots that, when printed, make up most of the colors of the rainbow.
If Process Color will print all these colors, why would you not use it for all your designs? Well, if a T-shirt image was not photorealistic, why would you want to print four colors when a simple Spot Color process would only require two? In addition, for most Spot Color images you want a more vibrant, solid image rather than a soft halftone dot print.
Process Color prints on T-shirts generally only work well on light colored shirts. The inks used are very transparent and do not work on Black. When printed on an Underbase of White ink, they become a little pastel. The problem with printing Process Color is that if you are not a good printer, or don’t know how to do the separations, the images will be muddy when printed.
Although Process Color separations are generally done by pixel based programs, these programs were designed for paper/offset printing and the program settings don’t allow for the fact that halftone dots grow in size when printed on a soft object like a T-shirt (dot gain). Process Color separations are generally NOT done with vector based programs like CorelDRAW.
For these reasons, Process Color is not for everyone. It generally requires better control, such as properly tensioned, high mesh-count screens and the ability to hold fine halftone dots and print them in register with minimal dot gain. The secret to good Process Color prints is in proper separations and good printing. Yes, you can do it, but plan to “experiment” a little, first.
Finally, when you see a vibrant Process Color print, it almost always has additional Spot Colors. What you think is just a CMYK print, may in fact have CMYK plus two or three Spot Colors to make the design really jump off the shirt.
Simulated Process Color
This is also known as “fake” process color. Simulated Process Color images have a photorealistic look but are not printed with the Process Colors of CMYK. They look like process, feel like process but they aren’t process. The color separations for Simulated Process Color are comprised of halftone images of Spot Colors like Red, Yellow , Blue, etc. They are often called “tonal” or “channel” separations. Simulated Process Color separations can be printed on light AND dark shirts and are generally done in Adobe Photoshop.
Because the inks for Simulated Process Color are generally all-purpose, semi- transparent plastisol, they give you a bright print even when printed on an Underbase of White ink. When done correctly, Simulated Process Color prints can be very photorealistic with smooth gradations and bright colors.
Over 90% of the jobs we separate for customers are done as Simulated Process Color.
This is probably the most confusing of the separation methods. For Simulated Process Color, CMYK Process Color and Spot Color with gradations, any shading is done with different size halftone dots that have a definite pattern and angle to them. Index Color separations are done in Adobe Photoshop and use random square dots that are all the same size. These random dot patterns are also often called diffusion dither or stochastic.
Moiré and Index Color
With traditional halftone dots, there is the possibility of getting undesirable patterns, called Moiré, when halftones are exposed on screen mesh and printed on shirts. These patterns happen because halftones generally need to be printed with a different angle for each color. If the angles of halftones are not correct, they create an “interference of two patterns” and give you a checkerboard effect.
In theory, Index Color separations should not give you a Moiré pattern because the dots are all the same size and they are random. This is one of the biggest industry lies ever told. No, you will not get a Moiré pattern within the separations, but if you use the wrong screen mesh (for example, a 200 DPI separation on a 200 mesh) you will get the worse Moiré you have ever seen.
Index Color separations are done in Adobe Photoshop by creating a color table of the most prominent colors in your image (and the most colors you are capable of printing). The software then converts the image to those colors using random square dots. Photoshop will make (or try to make) the image look as close as the original as possible with just the limited number of colors you selected.
The downside to index prints is that for the image to be photorealistic, you need at least six colors and in some cases eight to ten colors. Index prints can sometimes have a grainy and textured look to them. However, when printed with a lot of colors, index prints can be very striking!
Index separations work great for Spot Color images too. They are easy to print because you are placing a dot next to a dot, rather than printing halftone dots on top of halftone dots. However, just don’t use indexing because someone told you that halftones are hard. Most of the awards winning prints you see are still real Process Color and Simulated Process Color.
When do you use what method?
CMYK Process Color
Great for photorealistic images on White or light shirts. DO NOT use on dark shirts. Requires good separations, screen making and printing technique. The best process prints have additional Spot Colors. Prints may be a little duller than a simulated or index print.
Simulated Process Color
Great for dark shirts that need a photorealistic image but will work on light shirts too. Requires good separations, screen making and printing technique. Can print very smooth gradations and hold excellent detail. The most popular method used by award winning printers. Prints are bright because all purpose inks are used.
Works on light and dark shirts, but typically requires more colors than Simulated or Process Color (especially if going on Black shirts). Very easy to print because all the dots are the same size and you are printing square dots next to square dots rather than halftone dots on top of halftone dots. Separations are easy to do in Adobe Photoshop and screen making and printing can be forgiving. Very production friendly and easy to print. Images can have a slightly grainy (stippled) look. Works well for Spot Color also.