CMYK vs. RGB

Excerpted from Real World Print Production with Adobe Creative Cloud by Claudia McCue.
Copyright © 2014. Used with permission of Pearson Education, Inc. and Peachpit Press.

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Since the dawn of desktop publishing, it’s been unquestioned that Thou Shalt Convert to CMYK. Those who submitted RGB files were considered uninformed, even uncivilized.

The rules are changing, though, because of the increased use of digital printing. Although these devices may use inks or toners named cyan, magenta, yellow, and black, those inks and toners have a different pigment makeup than the namesake inks used on offset presses, and they have a wider color gamut than offset inks. Inkjet devices such as large-format printers utilize additional inks such as light cyan, pink, light yellow, orange, and green, further extending the range of colors that they can print.

This seems like a good time to open a can of multicolored worms. After you’ve been told by printers for years that you should convert your images to CMYK before submitting, I’m now going to tell you that you might not have to do so. That’s because many digital devices happily digest RGB and can provide more vibrant output by rendering RGB content.

When you convert to CMYK, ranges of colors outside the CMYK gamut are remapped to fall within the CMYK printable gamut, and some of your most vibrant colors are lost forever.

If you happen to have some very colorful RGB images (tropical birds would do the trick), try this little experiment:

1. Open the RGB image in Photoshop, and maybe make it even more vibrant by using Hue/Saturation or Vibrance. Get carried away; this is for science, after all, not for art.

2. Choose Edit > Color Settings. At the top of the dialog box, choose North America Prepress 2 from the menu and click OK.

3. Choose View > Proof Colors. The difference in appearance may not be huge, but try toggling Proof Colors on and off quickly by using the keyboard shortcut (PC: Ctrl-Y; Mac: Cmd-Y) and watch for differences in bright blues and greens. Neon greens provide a particularly noticeable difference.

4. Choose View > Gamut Warning. The gray areas are areas whose current RGB color will be remapped (and probably become duller) when converted to CMYK, because of the smaller color gamut of CMYK.

This gives you an idea of the color range that you’ll lose when you convert to CMYK—and much of that color range can be imaged on many digital devices. Of course, ask the print service provider before you submit your work to ensure that you’re sending what they want. Just don’t be surprised if they say “RGB is OK.”

RGB as a Working Format

Because the RGB gamut is larger than that of CMYK, it’s often preferable to perform color corrections and compositing with RGB files, converting to CMYK (if necessary) as late in the process as possible. If you are participating in a fully color-managed workflow, you will keep your images as RGB with ICC profiles. The International Color Consortium (ICC) was formed by a group of graphic arts industry vendors, with the goal of promoting the use and standardization of color management tools. ICC profiles are methods of describing the characteristics of devices such as scanners, presses, and printers for optimal results. Conversion will not take place until the job is imaged. Much of today’s software offers sophisticated support of color management. For example, when exporting a PDF or printing, InDesign will perform the same conversion of RGB to CMYK that Photoshop would (assuming you’ve synchronized your color settings across all your Creative Cloud applications).

What if the Printer Demands CMYK Images?

Some print service providers and their customers have fully adopted colormanaged workflows as part of their regular operation. But many print service providers (especially in North America) expect CMYK when you submit your job, believing that it’s what Nature intended, especially when the job will be printed on an offset press (as opposed to a digital printer). Consult with your printer to see what they prefer. If you’re using digital photography or scanning your own artwork, they should be able to provide you with their preferred settings, so you can make appropriate conversions to CMYK.

 

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Posted on: June 25, 2014

13 Comments on CMYK vs. RGB

  1. Trying to be Sandee Cohen

    June 25, 2014 at 3:01 pm

    As usual Claudia is perfect in her description of the process.

    But one thing she forgot is that InDesign’s Preflight flags RGB images as an alert. So even if you choose an RGB workflow with knowlege, you get an alert telling you something’s wrong.

    This alert is confusing for those outputting to print who have been told RGB is acceptable. It is a real nuisance for those who output for digital publications.

  2. One popular digital printer, CreateSpace, uses custom inks in their Indigo machines to create an RGB  space. They work with a lot of first-time authors, and it lets them provide a more-or-less WYSIWYG experience for covers and interior color work.

  3. That’s true; InDesign’s RGB paranoia is less warranted these days. Maybe the Yellow Triangle of Terror should be replaced with a friendly blue Asterisk of Information, with remarks pointing out that the designer should confirm with the printer whether RGB content is allowed.

    I still run into designers working with printers who insist on CMYK: I tell them to set their PDF export options to Convert to Destination. But that doesn’t fix the problem of truly archaic printers who also want the application files and will impose a surcharge for converting RGB images to CMYK. They’re rare, but they do exist. Sigh.

  4. lukasengqvist

    June 25, 2014 at 5:44 pm

    The big advantage of using RGB is that blend modes work much better. In CMYK there Screen and Darken blend modes work per colour and the can yeild unexpected results, also it is much easier to adjust colours without accidentally creating casts in a specific tonal range.

  5. Paul Sherfield

    June 26, 2014 at 8:26 am

    Yes, a can of worms indeed! Some comments. What RGB profile you use is important. SRGB in some areas of its gamut, i.e. blue/cyan is smaller then some CMYK gamuts. Also not all digital printing devices have a wider gamut then offset litho on coated papers, i.e. ISO coated v2 or GRACol. HP Indigos are very similar to offset and many toner based devises have smaller gamuts the offset. Wide format inkjet can be bigger, but then the issue of common colour appearance across differing printing methods can be an issue when printing a multi piece campaign.

    See my blog on this: http://www.missinghorsecons.co.uk/wordpress/2012/10/what-is-common-colour-appearance/

  6. John Clifford

    June 27, 2014 at 2:54 pm

    Claudia, another good example is to go into Photoshop and in the color picker pick a color at the extreme side (I use the upper right hand corner of a dark blue for in-class demonstrations). Note the little warning triangle? when you click on it, it shows you how that color would remap. The differences are astonishing to students.

  7. John Clifford

    June 27, 2014 at 2:57 pm

    Oh, and one more thing, if you’re using an ISO PDF/X format, you cannot use PDF/X-1a, which requires CMYK output. Only litho printers with newer APPE (Adobe PDF Print Engine) RIPs can process RGB. This might be the reason that InDesign is flagging the RGB. You need to set up your preflight profile to allow RGB or use PDF/X-4.

  8. Dov Isaacs (Adobe)

    June 27, 2014 at 3:16 pm

    From Adobe’s perspective, the most reliable print publishing workflow uses PDF/X-4 exported from InDesign or saved from Illustrator, making sure not to change any settings that would cause colors to be converted during the export/save operation. Keep live transparency and imagery in its original color spaces (with ICC profiles) with reconciliation with the final color space performed at the RIP/DFE where it should done.

    Some observations:

    (1) Although many printer service providers specify that they only take PDF/X-1a or CMYK-only files, some, including some major print service providers, will accept PDF/X-4. Ask!!!

    (2) Ironically, many of the same print service providers who insist of CMYK-only files (and everything preflattened) won’t provide you with information as to which CMYK they want you to convert the colors to. Some  have the attitude of “we don’t use no stink’in color management. We do ‘color-by-the-numbers.’” Such print service providers are simply looking for means of shifting blame if (and/or usually when) the colors don’t come out “right” – they are certainly not offering you professional “service” in any way 

    (3) In my experience, even if you encounter a print service provider who is clueless about PDF/X-4, I have found that if they are willing to learn, they quickly adopt and welcome such workflows as they see how much work it cuts out for them. VIrtually all RIPs and DFEs sold in the last  8 to 10 years (and software upgrades to older ones) support modern, color-managed PDF workflows with live transparency, such as is provided for with PDF/X-4. The problem is often that of print service providers keeping current.

    For those print service providers who despite it all persist and insist on customers providing pre-flattened CMYK-only PDF (as prescribed on the tablets handed down at Mt. Sinai), the only appropriate term I can think of is Luddite!

  9. Mike Witherell

    July 2, 2014 at 2:03 pm

    Ned Ludd is indeed an apt comparison.

    http://en.wikipedia.org/wiki/Ned_Ludd

  10. hi

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  11. For an in depth article explaining CMYK, RGB, and DPI, and how to get the perfect print, check out: http://youinkprinting.blogspot.com/2015/04/perfect-prints-dpi-rgb-and-cmyk.html

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