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Pre-Separate Complex Graphics with Index Tables

(February 2010) posted on Mon Jan 25, 2010

Trimingham explains how to use index dots to simplify the process of separating highly detailed garment designs.

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By Thomas Trimingham

An ongoing argument exists among printers who use traditional dots or index dots. Many believe that one is better than the other. The truth is that each method has its own advantage and that combining them, using both styles together in one image, can sometimes create the best possible file. Regardless, knowing how to use both styles of separations allows for simpler separations overall.

Index dots can be tested quickly and can often give a result in minutes, rather than an hour or two. That’s why they can work great as a separation pre-test to get a quick snapshot of a working set of positives.

Testing a graphic using a quick index-dot set
The best images for this process are ones that tend to cause trouble with a standard process. Dark shirt designs with blended colors, memory colors (colors that viewers recognize if they appear incorrect, such as wood, metal, or flesh), and lots of detail are good candidates for a pre-test using an index method. You can use one base design of a tiger to show two different, challenging printing methods: a more realistic version of the animal with a gothic background and a more modern approach using very bright, saturated colors (Figure 2).

The first design, which has realistic animal colors, is a good candidate for an index-separation set on the tiger and then a traditional halftone on the outside edge of the design that has the beveled elements. Soft, gradient transitions such as those outside of the design tend to look better using traditional halftones due to the reduction of the dot size as the halftone fades out on the print. An index dot in those areas would have a more abrupt look that might appear grainy if the dot size were all the same in the fading areas. An exception to this is when you can print and maintain a very fine dot size on screen, which typically requires high mesh count and tension, as well as refined ink viscosity and opacity control. In other words, it’s not something the average printer should attempt casually. To test the realistic design using a quick index separation set, I used the following steps:


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