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Hello I would like to ask how to do CMYK color separation for offset printing? Is it the same for screen printing i.e. spot colors? What would be the optimal DPI, Frequency and angles?

My mom sent me a single layer file to do color separation for offset printing.

Do I use photoshop or illustrator? Or is it something that is set on the printer rather than using photoshop or illustrator?

It's for a 3(H) x 5(W) ticket btw.

Thank you.

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    In general, you wouldn't do manual separations for offset. The Imagesetter or platemaker would handle separations. Is there a reason you need to manually do them?
    – Scott
    Commented Aug 12, 2015 at 18:41
  • Thank you for all the answers. :) The reason my mom sent me the files because she told me they said to layer it in CMYK for some reason... It boggles me as well why they sent it back, I guess I have to talk to my mom's contact... Thanks again.
    – user48306
    Commented Aug 12, 2015 at 19:46
  • @ Jereh Can you post a screenshot of your layers panel in Photoshop? If the printer sent the file back, it's because it's not in CMYK, and/or not at 300dpi @100% size, and/or there's no bleed. Your layers should also be flattened (1 layer only).
    – go-junta
    Commented Aug 12, 2015 at 19:52
  • "... they said to layer it in CMYK for some reason...." kind of sounds like she sent 4 files and they just want one CMYK file.
    – Scott
    Commented Aug 12, 2015 at 20:03
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    I feel this is too ambiguous. Foy your own sake, make a good designer to look on your files. There is a chance your project dont need a cmyk print at all or the file is totally wrong. This at the end costs money.
    – Rafael
    Commented Aug 12, 2015 at 22:19

3 Answers 3

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There are programs specifically designed to do this (AccuRIP, Separation Studio), but they are quite expensive; unless you're a print shop then that cost will be difficult to justify. As others have already mentioned, the print shop you're dealing with will likely do the separations for you (and probably have the powerful software to do so).

Within the Adobe Creative Suite, Photoshop is the tool you should use to do this. Illustrator has plugins available to produce vector halftones (Phantasm), but out of the box it's not the right choice. It does have some separation functionality built in, but not enough to prep your design for screen printed four color process.

If you're just interested in this at a hobbyist level, you can certainly accomplish this with just Photoshop. I don't deal with four color process screen printing very often so I'm reluctant to provide specific instructions but there are lots of resources available online covering CMYK separations within Photoshop. This video seems to cover it quite well.

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  1. First, make sure that it will indeed be printed on an offset printer because there are many printers who will print on digital printers where the input is expected to be RGB.
  2. If it will be offset printed, you may be better off converting your file to CMYK and letting them prepare the color separation. I presume you have a calibrated monitor. When you convert from RGB to CMYK you can judge the quality of the colors on your calibrated monitor.
  3. If you can obtain from the printer a device profile, you can do soft proofing to make sure nothing important goes out of gamut. If that happens you can make the necessary adjustments to bring them into gamut.
  4. Offset printing uses LPI (Lines Per Inch), find out what LPI they use on the requested paper and set your DPI to double that number as a rough guide. If they will print 120LPI set your DPI on the image dimensions to 240 DPI.

Conversion from RGB to CMYK is a lossy process so do this conversion on a copy of the file, once converted it will stay in CMYK.

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The color separation itself is done by the printer. All you'll need to do is send your files properly. You don't need to worry about the lineature and angle but only the resolution (ppi/dpi) of your files.

You should use 300ppi resolution in Photoshop (go in the menu "image" then "image size"). Be careful, the resolution must be 300ppi for the actual printed size of your document; you should see 3x5 and 300ppi in the resolution field. If you see lower than 266ppi or smaller document size, your mom might need to re-do the Photoshop layout again at the right resolution and size.

For your ticket, you'll need to make sure there's bleed applied to it if you have elements that should be printed to the edges (eg. no white borders.)

Add some trim marks to indicate the limits where the ticket will be cut.

Your colors should be in CMYK mode unless you are using a spot color printing process, for example you are using only 1-2 colors on your tickets. If it's printed at small quantity, it's probably on digital press and you simply need to make sure your colors are in CMYK. For this, look at the menu "image" then "mode" in Photoshop and select CMYK.

Yes, Illustrator is better for the text part, and Photoshop is better for the picture or photomontage part. Most designer like to import their work from Photoshop in Illustrator and add their text in Illustrator. You can also use InDesign to import both Illustrator and Photoshop.

Since your mom sent you only a one layer file, you can really re-do the text in Illustrator unless she sends you her real "psd" file with all the layers. It's still acceptable for a ticket to make the text in Photoshop.

I'm assuming you already know a bit about printing and how to use the software but you'll find a lot of details in this site about how to prepare your files!

As final file, you can export your work in PDF or TIFF from Photoshop.

For better quality of your texts:

How to keep the text in vector in Photoshop without rasterizing it or flattening the layers when exporting to PDF?

If you really want to create a color separation (which I don't think you should do yourself), you should do it using the "print" or command, and select the PostScript driver... then select "separation" in the output. You can also do this by "exporting" to PDF and creating a .ps instead. Really, it's usually the printer who does this step, so ask him if you're not certain. You can probably do it in InDesign.

How to do color separation

This will create a .ps file that you'll need to drag and drop on Adobe Acrobat Distiller, using the highest print settings. This will produce a PDF with your color separation; it should have 4 pages with black only on each of them.

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  • Good answer. One addendum, though: the 300DPI setting in photoshop pertains to photos and similar artwork. If, for whatever reason, you are setting type or line art in photoshop, you will want a much higher DPI setting (600, 1200 or higher depending on what it is you are printing and how).
    – DA01
    Commented Aug 13, 2015 at 21:26
  • I would better say don't ever rasterize type and vector objects. If possible, put type on top of any other parts. If not possible, for final solution, remember to rasterize all transparency effects (also layer semi-parentness or some kind of overlay). Do not send tiff file. It's totally superold format, useless size. Better flatten and send psd.
    – mrserge
    Commented Aug 13, 2015 at 21:40
  • Printer prefer TIFF, amazingly. PSD is not considered as a final file format by most of them. It's super old and still there because it works perfectly fine. And frankly DA01, there's way more stuff missing in this answer if we're talking prepress. This is a basic that probably fits well for a small ticket job done by someone who might be a beginner. Maybe you could link some complete guide from GD:SE that contains all the prepress tutorials, there must be one!
    – go-junta
    Commented Aug 13, 2015 at 21:53

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