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Color Consistency in Prepress

Talk about color consistency! More often than not, discussion centers on process control in the pressroom.

Still, considerations need to be accounted for in the stages leading up to the ink meeting the substrate: color separation styles and how to properly construct spot colors out of process builds.

Figure 1: The baseline fingerprint dictates everything that follows.
All graphics courtesy of SGS

Correctly address those two topics and your ability to obtain color consistency throughout significantly improves. Consistency relies on three main points:

Standards Establishment

Let’s start with standards establishment and an understanding of the criticality this step plays in the process. There are a lot of different “buzz words” in the industry around what this is and how to achieve it. The bottom line is, whether you call it a characterization, fingerprint, optimization, baselining or linearization, it’s crucial to pressroom controls.

Figure 2: CMYK depiction of impact of three levels of black generation and contamination, identified as No. 1, No. 2 and No. 3

Printing the required forms, regardless of what you are aligning to (Figure 1), is the most important pressrun performed and stressing this importance really cannot be understated. So, point made, let’s move on.

Once standardization is completed and everyone agrees the results are exemplary, the ICC profile (industry standard or unique) is utilized to color manage the conversion of the supplied files into the most effective color retouching and subsequent separations for the given print environment.

Figure 3: Black generation and contamination impact on cyan

Color Retouching

Files come to separators from all kinds of sources and in all kinds of color spaces, and sometimes they even come with a “target” that may or may not be a known entity. Given all of the effort to get the process standardized, we need to ensure the color separations come as close as possible to the intent, or target, at the same time that they provide the best possible separation for the press.

Figure 4: Black generation and contamination impact on magenta

The first step is to standardize the supplied files into something “known,” so the ICC profile that represents the print condition can be leveraged to convert the final separation style. In most cases, this will be done with automation software and converted into a GRACoL or FOGRA (for the EU crowd).

The benefit of using one of these spaces, aside from industry acceptance, is the fact that once the files are in this color space, downstream automation can be utilized to leverage the file for several different applications. Remember, a given image file can often be used on several different print processes, or even utilized for omnichannel and e-commerce needs.

Figure 5: Black generation and contamination impact on yellow

In flexography, there are unique considerations that go into the next conversion. This is the point where the separation can make a significant impact on print reproduction.

There are three image examples in Figure 2 that show the different levels of black generation and contamination, often classified in terms such as UCR, GRC, Long Black, Short Black, etc. For the sake of this discussion, let’s assume the proper style for this imaginary printer is style No. 2. This style can be collectively chosen at the time of the standardization process, in a print trial or simply based on expertise of the separator. The bottom line is we want to ensure this separation technique can be applied to all the files in a very consistent way (Figures 3-6 depict impact on individual color) that leads to repeatability in the overall process and on press.

Figure 6: Black generation and contamination impact on black

There are several options to perform this accurately. The best methods lean heavily on automation tools and applications that leverage the separation style desired through a device link ICC or RIP technologies that allow “device link on the fly” (Figure 7). Let’s not forget, this automation also allows for a potentially even more important aspect: the ability to convert from the GRACoL standard directly into the printer-profiled color space with a high-quality color match.

Once completed, color operators still have some work to do to ensure the file quality, specifically:

Figure 7: Automation tools and applications leverage separation style desired through a device link ICC, or RIP technologies, that allow “device link on the fly.”

Before we move on to the color builds, let’s recap:

  1. Standards establishment is absolutely critical to ensuring downstream color consistency
  2. ICC profiles confirmed to a standard or specifically developed, allow for consistent color space and separation style conversions that tie to automation technologies and produce a reliable, repeatable result

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