This article is from our design and pre press department (Julian) and explains the index separation process.

‘We often get called upon to produce colour prints from photographs or complex illustrations involving gradations of tone. There are several ways of achieving this, including transfer printing and direct to garment (DTG) printing. The most commonly used techniques for screen printing however, are index and simulated process. The following is an insight into index separations.

We have taken this photo of a handsome rooster and opened it in Adobe Photoshop.

The first thing to do is to decide on the print size and to make sure that the image is at a suitable resolution for screen printing.

This one is going to be a proud 11 inches and 160 ppi is good for retaining subtlety and detail without being too fine for the screens.Next we convert the image to index mode (image/mode/indexed colour).

With the preview box un-ticked, We open a colour table (palette/custom) and progressively pick out colours from the photo that we intend to be the final ink colours used in printing this minor miracle of the avian world. Here`s how it`s done.The first little colour table box we leave white. As we are going to be printing with 6 colours on white shirts, we now have 6 boxes to fill. The first box (after white) will give us the green which is mostly apparent in the fuzzy background foliage. Click in the box, then go up to an area of pale green on the photo. Click here and the box in the palette turns this colour. Click OK on the select colour box (which has suddenly appeared) and the first colour is done. For the next box in the colour table, choose the bright magenta from somewhere in our boy`s comb. The rest of the colours are a rich ruddy brown from his neck feathers, bright red from his wattle, pale yellow from his beak and that inscrutable black from his little alert eye (actually any black will do).

Click OK on the colour table.Click OK on the indexed colour box. Hit Alt+Ctrl+0 to get a view at actual pixels, et voila! Your indexed rooster. You can see the difference between the original and the indexed versions if we get a close up look at that eye.

What`s clear here is that by indexing an image, we turn it into wee contiguous blocks of discrete colour all of which we will separate and then magically re-combine to form a multi-colour print to thrill the onlooker.First we have to separate those colours. How can this possibly be done? Here`s where you need some extra software, specifically an index separation plugin such as Screenprint Separator. We simply export the index image through SS (as an illustrator file). After a cup of tea and a one of Lucy`s delicious pancakes we go to Adobe Illustrator and open up the file just exported from Photoshop.

What we have now is our incomparable bird on screen with all the index colours fully separated on their own layers. At this stage other material such as vector graphics or lettering can be added to the design. The separations can now be printed out individually as pure black, onto film, with printer`s registration marks. To cut it short, each sep gets transferred onto a screen to be printed through onto the shirts with the appropriate colour ink and Bob`s your Uncle. Needless to say, the client is overcome with emotion.’

T-shirt Printing

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