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Prepping Artwork for Fast Separation

(October 2011) posted on Tue Oct 25, 2011

Rushing the separation process can lead to disaster in production. Find out how to determine which approach represents the best mix of quality and speed for your shop.


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By Thomas Trimingham

Four-color process
Separating the images for four-color process was deceptively easy. The files were just converted from RGB into CMYK with black at maximum. The part of the process that took the most time was looking over the images and making adjustments to the sections or areas of color that wouldn’t print properly. There was a tendency for the separations to have too much black in them and some unnecessary ghosting of cyan and yellow in the red areas, so these had to be corrected manually prior to finalizing the channels.
Separating the files into four-color process with the added time for correction took 35 minutes each. The number of colors was four with an added underbase color for dark shirts.

The critical consideration is that four-color process requires intense control of press, ink, and garment variables to have a consistent look to all the garments through a printing run. These concerns make four-color process a big challenge for many screen printers. This approach to color separation is image dependent. Many printers won’t touch a four-color job on dark garments because of all of the headaches, but on white garments, with the right artwork, this style of printing can capture the widest array of colors.

Index color
Both of the test designs happened to be good candidates for index separation, so the test in a sense wasn’t quite as balanced. Index separations require a good understanding of how to manipulate an image’s color table in Photoshop as it is converted to an index-color design. Therefore, operator experience can really play a factor in separation speed.

Index separations are the fastest of the three types of separations discussed here. The final results for both designs were obtained in less than ten minutes. The time included some significant tweaking of the color table to allow for some blending and some underbase extraction.

One downside is that index separations take two to three times as many colors to work as the other methods—in this case, eight or nine colors each. The other major concern is that all of the colors are opaque in an index print, so nine colors were mixed to match what was in the file separations.
The flaws and advantages of index prints really go along with a shop’s production style. If a printer has a large press with a lot of mixed inks already, that might be a perfect environment for index printing.



Simulated process
The most popular style of separations for detailed art is defined by its ability to blend and create multiple colors and be friendly in production with minimal gain. Images can be adjusted to fit stock inks, thereby saving on mixing time.

Another advantage of simulated process in these tests was the ability to limit colors to six on both designs. The production of simulated process is more of a challenge in screenmaking than it is on press. Screens have to be made carefully to capture any subtle dots and shades to prevent loss of details in the design.

The drawback of simulated process is the time it takes to separate effectively. Even with a small amount of scripting—it’s easy to program a list of commands to create an underbase and highlight color—the separation of the test designs took 45 minutes each. Considerable adjustments were made to the final separations to ensure proper testing and printing without difficulty.

Summing up the results
The overall review of the different separation methods for speed and quality showed that while simulated process produced the best balance in profitable prints, it was the slowest in separation. Index color was worth a second look just for the fact that it is exceedingly fast to do—but it does create extra colors and needs a lot of custom inks. Four-color process was the most troublesome on the press and the most nerve-wracking for a learning screen printer to separate. In considering all of the test results, simulated process still leads in overall quality and printing ease; index color comes in a clear second for its extremely fast test times; and four-color process remains in last place because of its temperamental results.


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