plaid_rabbit t1_j1y3vyb wrote on December 28, 2022 at 6:29 AM

The tricky part is defining “CMYK conversion”. A strict “technically correct” conversion tends to look terrible.

The way you do colors on a screen is by blending RG and B light. This is called additive color. CMYK adds pigments that block all but a specific band of light. There are some colors that are super hard to reproduce in one or the other. A nice dark four color black is impossible to reproduce on a monitor, not just because it’s hard to get the screen super-black, but it also doesn’t absorb light reflected off of it. It’s not of it’s surrounding, it’s it’s own light source.

So you have to consider a lot of things when you talk about CMYK colors… like how white is the paper you’re printing on. A super bleach white paper vs newspaper, which is very gray-ish. If you spray a light mist of say red spray paint on each, they will come out to different colors. So what do you use for your baseline for your RGB-CMYK conversion? Now are you doing this with natural light, incandescent lights (which are slightly yellow) or LED lights (which tend to blue).

Pantone dodges this whole problem, and says what the finished product should look like. It’s right when it looks like the swatch from the book. And ink manufacturers make inks that you can put a thin solid coat down and hit the target without question.

ExternalUserError OP t1_j1ym42o wrote on December 28, 2022 at 10:35 AM

Thanks for the explanation.

So when you use a Pantone color in Photoshop, there's extra data there about what inks to use, etc? It's not just the RGB value stored in the file, it's the actual Pantone color?

So for example, if I have a Photoshop file with Pantone colors and I take that file to a printers, they know how to print it better than RGB? Is that fair to say?

pselodux t1_j1z0x65 wrote on December 28, 2022 at 1:30 PM

Yes, it separates the Pantone colour out almost like another layer.

When you usually send something to print, it gets converted into four colour layers—cyan, magenta, yellow and black. These become individual printing plates (or toner/ink layers in digital print), and mix together using dots at different densities to achieve the colours you used in your file.

If you use a Pantone colour, it’ll be converted into its own layer/plate, and printed using the selected Pantone formulation. This will be noticeable next to a CMYK mix because it’ll be a nice flat colour, while the CMYK mix will be made up of patterns of dots from each component colour.

edit: you don’t actually need to specify Pantone colours to do this either. You can simply set a colour as a spot colour and it’ll appear as its own plate (also known in software as a separation) for the press.

plaid_rabbit t1_j214ece wrote on December 28, 2022 at 10:13 PM

In the file, it stores "This item is pantone-1234", and lets the software using the file figure out what to do with it. So when it's rendered to screen, it uses a lookup to pick a good RGB color. When it's printed in CMYK it uses another. When you check it against what light it reflects, that's it's own set of rules about what it's "supposed to" look like. Fancy industrial printers have the ability to load specific inks for specific colors. So a press might support 4 colors, which you normally load CMYK. But let's say you're making a bunch of pamphlets for one company, which is black and white, but they want their logo on each page. You can load Black, and 3 other customs colors in instead. Some machines support something like 8 colors, just for this reason. Sometimes you need to load white ink because your printing on non-white materials. CMYK is just the most basic way of printing color.

maartenvanheek t1_j1yg7dg wrote on December 28, 2022 at 9:11 AM

... So a Pantone printing press has interchangeable/unique ink reservoirs for each pantone? Isn't that impossible to manage or very expensive to maintain a large stock of unique inks? Or do I misunderstand.

Noctew t1_j1yi5dp wrote on December 28, 2022 at 9:39 AM

It is more expensive, and you would not have all Pantone colors available. But, as a printing house, when your customer like for example DHL tells you: "I need cardstock for 1 million envelopes printed with our logo, and it has to be PMS 2035 C red on PMS 116 C yellow." then you buy that exact inks from a printing ink manufacturer and print your cardstock - and if your paper was the correct brightness and the ink manufacturer has mixed the inks correctly, the colors will be perfect on the first attempt.

w0mbatina t1_j1yj39y wrote on December 28, 2022 at 9:52 AM

A lot of pantone colors are actually a mix of more basic pantone inks. For example Pantone 7416 U can be created by mixing 16,70% Pantone Yellow, 16,70% Pantone Rubine red and 66,60% Pantone Transparent white.

You still need to carry a lot more inks than just the standard CMYK, but its somewhat manageable. For large runs you just buy the pre mixed inks, but for smaller jobs you can mix them yourself.

plaid_rabbit t1_j26rg3p wrote on December 30, 2022 at 1:35 AM

You’re not quite envisioning the setup right. These machines use buckets/barrels of ink at a time. You pour the ink in.

And you don’t have one for each Pantone, but you can have a few tanks that you basically set up per run. So in the example where the guy is talking DHL, you might load it with black, pms 2035c and pms 116c. (I assume those are the official colors). When you’re done printing out the million envelops, you dump out any extra ink, and clean the Pantone ink out of the press, and load it with the correct colors for the next job.

dperry1973 t1_j212ojk wrote on December 28, 2022 at 10:01 PM

Any commercial printing press will have capacity for CMYK ink plus multiple Pantone inks. A machine called a raster image processor reads say a PDF and generates individual printing plates for every color specified by the designer/client. A designer will apply Pantone color stickers to the ink jet or laser printout that the designer sends along with the digital file so that the print shop can prepare the printing plates and Pantone inks for the job. A machine like the automated paint mixers in a hardware store are used to mix up Pantone inks that a print shop doesn’t have on hand. There’s obviously an upcharge for custom inks which the cost is tacked into the bill. Clients will fire a designer for allowing the wrong Pantone colors to go to press. If a Pantone code is in the specification doc isn’t used by the print shop, the print shop will eat the cost of the mistake. There’s a “nobody got fired for choosing Pantone colors when it matters” mentality amongst designers and printers.

dperry1973 t1_j1y16eo wrote on December 28, 2022 at 5:59 AM

"So was the CMYK conversion impossible or just rushed? Like if you took the Pantone color you wanted to a color matching computer or something, and printed out a CMYK, they’d still be different?"

Converting to CMYK causes a color shift because Pantone's spot ink formula has at times no 100% direct translation to CMYK. Spot inks are more like paint at the hardware store where RGB/CMYK is like scanning a paint chip from one store and having another store mix it. Sometimes the results are a bit off.

"And how does this work for a computer file?"

It's all coordinated magic between the graphics software, your operating system, and the output device. Your graphics app embeds a color correction profile which the OS uses to instruct the printer how to match the colors. But this tech is not a 100% rock solid science. Sometimes math doesn't convert colors correctly. That's why us old-timers will get a test print from the print shop before making an expensive mistake. Technology can fail.

ELI5: How is that Pantone colors don't have direct RGB counterparts?

ExternalUserError OP t1_j1xvjjv wrote on December 28, 2022 at 5:02 AM