Index Separation Method for Screen Printing
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.’
If you found our design department enlightened you in any way with this article please leave a comment
Very interesting, it is great to see what techniques are used by screen printers, so that designers (like myself) can understand how to approach you with our designs.
Approach with caution, especially before morning coffee.
es muy bueno sabes de algun metodo de index y process simulate al mismo tiempo. esta muy bueno y me gustaria saber mas….
I like it’s very interesting… do you know how to make a process simulate and if you put on in the blog .. i work in Ensenada, B.C. Mex.
Mike we will hopefully have some simulated process information on the web site soon, this is a little more involved than the index separations, but I am sure we can outline the process and give some tips. Thanks for your comments.
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hello screenprinters
a quick inquiry regarding index seps:
is there a general rule about the ratio between artwork resolution|(dpi) and mesh count (t)?
i’m working on a print job onto paper and the artwork is 150dpi. i plan to use 77t screens in the understanding that the mesh count should be half that of the dpi (77t to 150dpi).
can anyone help?
much appreciated
will
Hi Will, if you are using the index separation method you can disregard the dpi to mesh ratio to a point, it is not critical as it is a random dot, as you are printing on to paper you are possibly looking for the max resolution you can achieve, when printing textiles we use anything from 150 to 200 dpi we have achieved these resolutions on many different screen meshes, but when paper printing you can use the finest meshes.
I love the method, and i guess there will no need to worry about those
evil dots in 4 colour separation anymore.Thanks very much for the information.
Hi Peter, some patterning can occur with index printing (shock horror!) we have been fortunate enough to have only experienced once or twice, 200 dpi on a 90T being one. We tend to try things out rather than rely on vague formulas, there are pleasant suprises as well as disappointments for both AM and FM halftones.
[...] Help with Printing Smoke/Ghost Effect I like these guys Index Separation Method for Screen Printing but the answer is yes, that’s a reasonable way of doing it. __________________ Copyjet imagesetter [...]
Interesting to see the technique used. Is the Screenprint Separator good at its job? Or do the files need tweaking afterwards?
The colour separation software I have looked at before wasn’t very good. Would be interested to hear if it can do what it says on the tin!
Hi Sid
Personally I don’t think there is any separation software that works out of the tin, most files will need tweaking to suit a screen printers set up, and inks. Wilflex have a separation system that has been created for their own inks, this is one we have yet to try. Screen print separator is very useful software and a worth while addition to your actions pallet, but just one of many solutions a screen printer should have, index printing ideally requires many colours 8+ to reach its full potential. Hope this helps.
[...] colors, tones that are defined from various sizes. To give you more insights, here’s a link: Index Separation Method for Screen Printing index separation CHEERS! __________________ Mag-print tayong lahat para [...]
[...] index-method-for-screen-printing [...]
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