How are Spot Colour/Process Colours read when sent to print?


Hi all,

I have been brushing up on my use of document colour settings in Adobe InDesign/Adobe Illustrator and have a question:

When you bundle your colour information in the swatch panel (indicating which parts of the design are CMYK and which parts are spot PANTONE colours) and export it as a PDF to be sent off for print, how is that information read at the print end - i.e. does a human check the document and go 'Oh, this bit is a spot colour, those bits are C,M,Y and K...' or is the information processed by the on-board CPU of whatever printer/plotter is being used?

I assume a human checks everything first when printing lithographic off-set printing as a plate will need to be handled manually at some point, but am not sure how it works with digital print?

In the past, there have been jobs that I have sent to printers (simple paper pieces like wedding invites etc, which I imagine will have been printed digitally) without any knowledge of how to properly set up the print specs for the document. Perhaps by fluke, these have come back OK.

Since I work in the same building as our screen printers (we deal with textile printing mostly), the separations I deal with are virtually always spot colour based (we rely on digital printing for any full colour stuff as the runs are generally small enough). Any decision relating to what colour process to use is often made on the fly and pretty informally.

Just curious about how it all works at the production end.

What ramifications does this have on the designer at his/her end at the point of document setup, has anyone got any juicy horror stories?




Staff member
Typically I would only use Pantone Spot colours for branding - if it's not branded and require a specific colour then Pantone is not required.

Pantone are as set of colours that are mixed inks at a printers, they mix the inks at the shop to match the branding. Pantone books show what these look like on coated and uncoated paper.

If you have spot colours in your document then they are setup alongside the CMYK colours to be output as individual plates. This is important for lithographic/flexographic/screen printing - but digital printing, some can use spot colours in digital, but mostly it's just 4 colour.

Files are typically checked by a prepress operator who will take the job on. Firstly the job is agreed by an estimator who will cost you the work and setup a job bag which will indicate if it's CMYK, Spot or other type of printing work.

The prepress operator will take a look at the job bag and examine the files to ensure that they are as supplied. For instance, in lithographic printing you'd want a 2 Colour job to be supplied as Pantones - in two colours - and that's all that should output. This would output as 2 plates. Compared to if it was 4 colour it would output on 4 plates.

And a plate is metalic object, with emulsion that is burned off (mostly laser these days, but used to be UV) - so there's a price per plate, I don't what they are these days, but roughly £20 a plate. 4 plates would be £80 and 2 plates £40.

Spot colours in Pantone are the best way to keep colours consistent.

If your sport colour is just called "Company Green" I've seen those even though the colour is green on screen - this can be output in digital scenarios as purple, or yellow.

I know weird right! Well that's because the digital printing press will have a RIP (raster image processing) where it needs to send the data and assign the colours. "Company Green" wouldn't be in the digital press library of stored colours for printing - so it would assign a colour, and it may or may not be green.

Makes sense. It's up to the prepress person to catch this.

And pantone colours can be assigned CMYK values by the prepress operator IF the job is supposed to be 4 colour - then the RIP will convert the colours.

What happens if you have Pantone colours - in litho/flexo/screen you get separate printing plates/screens.
When I worked for a print shop, if it was offset (litho) depending on what it was, we'd make sure the customer understood that using PMS colors was expensive and send them a quote. If it was digital, we'd make sure the customer understood that we can't match Pantone shades with CMYK, we'd go to the Pantone website, find its closest CMYK equivalent and change it to that. Usually it was pretty close. If it was really far off we'd bring the customer in and give them samples.

Now I work for a sign company and the RIP we use on the giant digital flatbed is... weird. If you input CMYK 3 100 70 12 (Pantone 200's equivalent) more than likely you'll get a nice shade of orange. But Pantone 200 is more of a blue-red. However, if you input Pantone 200, you get something really close to Pantone 200. So we use Pantone shades for literally everything because we can't predict how CMYK values will actually turn out. It gets super complicated when people send in stuff with gradients... because if you've ever tried to make a gradient between 2 Pantone shades... It just doesn't work.

Color matching is weird. Basically our solution was to print out a giant piece of steel (we pretty much exclusively print steel signs) with all the Pantone shades on it, and show it to customers and say "your custom green is probably close to this one, but these are the colors we can print"

My point is.... Every print shop is totally different with how it handles Pantones, but at the very least, using them gives the shop an idea of what color it's supposed to be sorta.