03 June 2010

Bit by Bit: Why Your Photoshop Color Separations Are Wrong -- and How to Fix Them

Recently I got involved in a project studying the gamut of color available printing with CMYK (cyan, magenta, yellow, and black) inks versus that of several expanded-gamut printing processes. Expanded-gamut processes are those that use more than the typical four ink colors to express color images with brighter greens, reds, and blues. Pantone's Hexachrome is one example of an expanded-gamut printing process.

When I queried the printer who will be testing the colors in the study about how he wants his color separations made for traditional CMYK pigments, he responded that I should "just make them with Photoshop." When I asked for detail, he said, "Just pull-down the Image menu, then Mode, and then pick CMYK."

And right there is the crux of a problem that besets our industry: Most of us are converting to CMYK wrong. The method he described would result with the wrong default CMYK profile set. That he did not state exactly how to make a separation for his exact printing process indicated to me that he was working with the default settings in Photoshop. That worried me -- and made me think.

The SWOP Meet

I am going to stick my neck out here and guess that as many as 90 percent of Photoshop users in North America (I'll focus on this continent for my assertions in this article) make their color separations wrong. That's because Adobe Photoshop is set by default to make CMYK color separations with the SWOP profile. And, I will also bet that fewer than one percent of Photoshop users should be using SWOP for their separations when there is a far better way to do it located in the same Photoshop folder of available profiles.

Now it's possible that some of you don't know what SWOP stands for (thereby adding to the problem): SWOP is the Specifications [for] Web Offset Publications, a North-American standard adopted by the advertising industry, the prepress industry, and a number of publications printers. It is specifically directed to Web Offset Publications -- and I'm not talking about the World Wide Web, either.

I know we all read web offset publications ("Newsweek" and "Sports Illustrated" are two good examples), but few of us prepare artwork for web offset publications. Of all the designers in my circle of friends and associates, only one produces artwork for web offset. Most are busy preparing for sheet-fed offset, which is the means by which most jobs are printed in the world (web wins in the volume category, but certainly not in the number of jobs). That number includes the printer testing the colors in our expanded-gamut study. We were indeed preparing files for a sheet-fed press.

Yet, I'd wager that most of make separations as if we printed to web presses, and we don't even realize it's a problem.

Photoshop's Dark Ages

How did this come to be? Way back in the Dark Ages (defined as 40C, 30M, 35Y and 100K), Adobe Photoshop assumed that all the color that was reproducible in any document had to be within the gamut of color that could be displayed on the monitor. This assumption was not only incorrect, but it caused Photoshop to be derided by prepress professionals (especially those who had access to very-high-end equipment including drum scanners and proprietary prepress computers that could handle the full gamut of CMYK for quality printing). These experienced craftspeople noticed that the color that came from Photoshop was not as rich as the color produced by their more advanced prepress technologies.

Several people on the Photoshop team noticed it, too. Led by Chris Cox, a member of the software development team for Photoshop, the group came up with a plan to give Photoshop a better grasp of color. The result was Photoshop 5.0, which, in October 1998, decoupled the color in the image from the color on the monitor for the first time. They developed and shipped the first version of Photoshop that used what is called the Working Color Space, effectively an ICC profile that describes a triangular space inside of which an image's colors reside while the observer looks at a monitor with an often-smaller gamut of colors (see Figure 1).

Figure 1: The gamuts of monitors, images, and presses do not match -- no wonder it ws tough to get good color seps from Photoshop!

Instead of heralding this achievement, most of us were left befuddled. It took me months to get a clear picture of what had taken place, and according to one friend at Adobe, the tech-support lines nearly rang off the wall for weeks after version 5.0 shipped. Adobe had unleashed a monster, and the industry wasn't quite prepared for it.

Of the several settings added when Photoshop 5 shipped was the default conversion to CMYK into the SWOP color specifications. The RGB color default was set to sRGB (also incorrect for most professional graphic arts purposes). The Photoshop team adopted SWOP and sRGB as defaults because they were established standards at a time when no others existed. (To date there is no sheet-fed standard, though one is under development; the Adobe CMYK profiles mentioned below are the closest thing we have to an accessible standard today.) The changes to Photoshop caused a minor problem for creative professionals, but once we learned how to use the new tools, we could see that the color is visibly and measurably superior to those color separations from the pre-Photoshop 5 era.

I also applauded the developers for adopting the ICC standard for all color conversions in Photoshop, including RGB, CMYK, Lab, and the internal Working Color Spaces. For the first time it was possible to make accurate and correct color separations using Photoshop. Anyone can do it, and all you need to know is how to set some of the preferences in the application.

SWOP Stories

So the SWOP standard has been, since version 5.0 of Photoshop, the CMYK default for the program, and as a result is the standard to which color gets converted on those 90 percent of users' machines.

Yet because most print-oriented Photoshop users who create color separations print our work on sheet-fed presses, we are blindly making color separations for the wrong process. Let's look at the details.

The SWOP standard includes the following assumptions:

  • Web-offset printing at high speed (20,000-60,000 impressions-per-hour);

  • Heat-set drying;
  • Semi-gloss pulp-based paper stock;
  • 133 lpi halftone frequency;
  • Elliptical-dot halftone patterns;
  • 95 percent maximum shadow dot.

Hmmm. When I look down that list I notice that not even one characteristic is common to the work I prepare. I create art for high-quality sheet-fed offset with these characteristics:

  • Slower press (usually less than 10,000 impressions per hour);

  • Air-dried ink;
  • Fine-gloss or dull-coated papers;
  • High-frequency halftone (usually 150, occasionally 175 lpi) and very tight register;
  • Modified round-dot halftone pattern;
  • Maximum shadow dot determined by the printing process and paper.

No wonder separations don't look as good as they could when we use the SWOP settings. They're very different animals. Separations for sheet-fed printing, made with the correct profiles, are better for the sheet-fed process.

Swapping Out SWOP

As better color is very appealing to me, I want to make a proper CMYK color separation for sheet-fed printing. When you use the right separation profile, you'll get better highlights, measurably deeper shadows on glossy paper, and a larger color gamut. Making the right kind of color separation will yield a result that will make you and your client feel better about printing.

Adobe has made it easy to get it right in the more recent versions of Photoshop (6 and 7). To clarify the many color settings, recent versions of Photoshop classify them into categories of work. This makes much more sense, and guides people who use the program to choose settings that match the work they do. These are the available presets:

  • Color Management Off

  • ColorSync Workflow
  • Emulate Acrobat 4
  • Emulate Photoshop 4
  • Europe Prepress Defaults
  • Japan Prepress Defaults
  • Photoshop 5 Default Spaces
  • U.S. Prepress Defaults
  • Web Graphic Defaults

By choosing from the list the kind of work we do (primarily prepress or Web graphics), the basic settings are closer to being correct than allowing the program to default to an unknown or incorrect set of defaults. By changing one of the defaults in the prepress defaults, I get a very good combination of settings that serves my needs well.

Here is how to do it:

  1. Open the Color Settings in your Photoshop application (depending on the version, this is either under the Photoshop, File, or Edit menu).
  2. Check Advanced Mode.
  3. Choose U.S. Prepress Defaults from the pull-down menu entitled: Settings.
  4. Change the Working Spaces: CMYK to U.S. Sheetfed Coated v.2 (see Figure 2). If your work is designed primarily for uncoated sheet-fed printing, you should choose U.S. Sheetfed Uncoated v.2 as your Working Space.
  5. Save your settings (which until you save it will be called "Custom" -- give the settings a name like "My prepress defaults."
  6. Choose the Adobe ACE engine if you prefer Adobe's software; choose Apple ColorSync (aka Heidelberg on Windows machines) if that is your preference.
  7. Click OK, and then take the rest of the day off.

Figure 2: You can create you own custom settings as I did here, or simply use the defaults for sheet-fed presses -- coated or uncoated. Either way you'll get better results.

The two available sheet-fed profiles that come with Photoshop are extraordinarily effective. Though I prefer to use a custom profile for a particular press and paper combination if one is available, these profiles do a much better job for sheet-fed printing than SWOP will ever do.

And, next time you convert from RGB (digital camera, scanner, original art) to CMYK, from Image> Mode, you'll get a better separation from Adobe Photoshop. The results are visibly better, and should please everyone in the reproduction chain.

And, for the one percent of you who are preparing art for heat-set web-offset printing: use SWOP -- that's what it's for.

Author by Brian P. Lawler.