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Author Topic: Colors are different when exporting to CMYK PDF (to Printer)  (Read 186 times)

bcnx

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Colors are different when exporting to CMYK PDF (to Printer)
« on: February 14, 2019, 12:42:57 am »
Hi all,

I'm designing the artwork for a CD I'm about to release in Scribus. I love open source, so I prefer it to Adobe products. The printing house requires PDFs in CMYK, so that is what I export to. However, when I open the PDF, the one grey color I use is lighter than the original (I check with Kcolorchooser). When I export for Screen/Web, the PDF has the correct color. Things I did:
- did some research in this forum
- enabled Color Management
- replace the RGB color with its equivalent CMYK value
- trying different PDF versions (1.3 to 1.5)
Will the PDFs I exported have the correct color, even though my screen tells otherwise? Or should I intervene somewhere so the situation for CMYK produces the same results as for RGB?
I'm on Linux Mint 18.2 with Scribus 1.4.6.

Cheers!

BC
« Last Edit: February 14, 2019, 01:21:38 am by bcnx »

bcnx

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Re: Colors are different when exporting to CMYK PDF (to Printer)
« Reply #1 on: February 14, 2019, 02:02:11 am »
Update: I enabled color management in the Document Setup. This turned my design immediately very dark, but when choosing certain ICC profiles in the PDF export window, I came very close to the correct color (Kcolorchooser showd RGB 84/84/84, while it is 85/85/85).
Will experiment some more with other profiles.
Does anyone know why my design turned so dark all of a sudden?

cheers,

BC

mnawij

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Re: Colors are different when exporting to CMYK PDF (to Printer)
« Reply #2 on: February 15, 2019, 05:20:47 am »
Hi bcnx,

I have attached a color gamut range diagram that shows the various ranges of colors.  Google CMYK vs RGB gamut for better explanations.  Those are just two gamuts, there are 3+ different RGB that I know of and usually the gamut range changes with each print driver when you print digital...  Notice that CMYK is a much smaller range, so when it gets converted from RGB there are much less colors to choose from and it automatically adjusts to the closest color possible.  You are on the right track in choosing ICC profile that comes closest to what you want but when going to CMYK always get a proof printed from a color calibrated press.  Notice though that when choosing ICC profiles, going from RGB to RGB will not accurately demonstrate what CMYK will convert to.  Hope this helps.

Cheers!
mnawij

bcnx

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Re: Colors are different when exporting to CMYK PDF (to Printer)
« Reply #3 on: February 15, 2019, 02:52:30 pm »
Hi,

thanks for your elaborate reply!
In the meantime I got news from the printer that they use the FROGRA 39, so I assume I need to use that one. This profile also warps the colors however when converting a color from RGB to CMYK. My solution was to experiment until the right color showed up on screen. I'm not sure this is a good thing to do?

Cheers,

BC

Nermander

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Re: Colors are different when exporting to CMYK PDF (to Printer)
« Reply #4 on: February 15, 2019, 11:52:53 pm »
No, because for showing on screen the CMYK colors need to be converted "back" to RGB, because the screen cannot show CMYK colors.

That is the major problem that mnawij tried to explain.

A "color" in a digital file is just a number. What color that number represents depends on the defined colorspace. But no device can reproduce all possible colors. That means if the colospace has a larger gamut than the output device (printer or screen) you will get a conversion.

The only way to get colors to show in a decent way is to have correct profiles for your output devices. That is done by outputting "numbers" and then measure what color those numbers give. This is often incorrectly called "calibration", but the correct term is "profiling".

For a monitor you usually use a "spider" to measure the colors on screen, for a printer you can send prints to a company that can measure the colors and give you a profile back. There are "poor mans solutions" using a scanner, but the scanner must then have been profiled first (using what is called a "target").

Note though that for a printer the profile depends also on the paper used, so different papers will give different colors.

Unless you have profiled your devices properly I think it's best to work in RGB and then convert to CMYK using the printer's suggested profile.

bcnx

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Re: Colors are different when exporting to CMYK PDF (to Printer)
« Reply #5 on: February 16, 2019, 02:32:29 pm »
Hi,

OK, thanks. I'm all new to this, as is apparent.
So, while doing DTP work as a layman (with no spider and a simple laserprinter ), you are basically working blind until you see the printing test made by the printing service?

cheers,

BC

mnawij

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Re: Colors are different when exporting to CMYK PDF (to Printer)
« Reply #6 on: February 17, 2019, 05:57:26 am »
Yes, that is the case unless your are willing to purchase some color books such as  https://www.pantone.com/products/graphics/cmyk-coated-uncoated.  Worth their weight in gold if you plan on designing for any length of time.  Using a guide like this will get you near the right color every time, but you still have to deal with the various ICC profiles for each printer which will vary the color a small bit and whether or not you print offset, digital, etc... which also can vary the color a bit, but as I said it will generally get you near the mark.

Cheers!

mnawij

Nermander

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Re: Colors are different when exporting to CMYK PDF (to Printer)
« Reply #7 on: February 17, 2019, 08:57:28 am »
So, while doing DTP work as a layman (with no spider and a simple laserprinter ), you are basically working blind until you see the printing test made by the printing service?

Essentially yes.

Even professionals were working like that way back. That is the reason color management was invented, get rid of all those test prints. I remember that we first got B/W laser printed drafts for proof reading. To check colors we received copies printed on a sublimation printer. Then for "final proof" what we called "blue print" (from what I understand it was printed from the film that would be used to make the actual plates, but everything was blue)

But getting color management to work 100% takes some effort. Like you have to hav consistent and neutral lighting in the room where you work ("gray walls"), devices need to have their profiles checked or updated regularly etc.


But a spider for profiling your monitor is not extremely expensive, and for printer you can find services that you send your prints to and then get a profile.

Now I'm, not sure if these prices are the best, these are just a few quick googled results. If you are really interested you should google around a bit yourself.

Here's an example of a spider for monitor profiling.
https://www.amazon.com/ColorVision-S2EL100-Spyder-3-Elite/dp/B000X4X35C

And here's a service (in UK it seems) that can profile your printer.
https://www.colourphil.co.uk/profiling.shtml

 

palmate