Rich blacks don’t always come about intentionally. Sometimes they creep into a design unwittingly, for example when some artwork originated in RGB.
This article is published as part of the exclusive AG blog series Avoiding 10 Illustrator Publishing Pitfalls 
No – it’s nothing to do with a color’s financial status. “Rich black” refers to a deep black defined in CMYK using a high levels of Cyan, Magenta, Yellow and Black. Wikipedia features this page to describe rich blacks.
Isn’t black ink on its own enough? Well, not really. The trouble is that all inks are semi-transparent to different levels. It’s accepted that you can see right through yellow ink and that it only displays a low level of opacity. But neither is black completely… black.
To make a printed result “blacker” on an offset press, there are a few common tricks:
- Running the page through the black ink station twice for a “double hit”
- More commonly, if the print job contains more than just black ink, add levels of Cyan, Magenta and Yellow or spot ink(s) to make the black richer and deeper
- Sometimes, coatings also enhance a black’s visual depth
However, rich blacks don’t always come about intentionally. Sometimes they creep into a design unwittingly, for example when some artwork originated in RGB. If Illustrator converts RGB black to an equivalent CMYK definition, it’s doing the correct thing by adding other inks to the party in an attempt to match the pure black possible in RGB. The second way to introduce rich black, especially into vector artwork, is through using Phantasm CS’ color tools including Curves, Levels and Brightness/Contrast.
Why’s rich black a bad thing?
Problems start on the print press, especially with more traditional offset presses. With these presses, each ink is applied at a separate unit and the page has to travel mechanically between these units, often at great speed. Even though modern presses have excellent accuracy and control, a very slight error in accuracy is inevitable meaning that each ink’s impression is not always perfectly aligned producing mis-registration.
Above is a simulated magnified example of a printed piece where the plates don’t perfectly align. The image appears blurred and is something familiar on newspapers where the printing methods compound the potential for mis-registration.
The problem is bad enough in a photo. Now imagine the effect it would have on fine strokes/lines defined using all 4 process inks. Re-visiting the title image to this article brings this result to reality… a bit of a mess!
As another example, the following text is defined in a rich black that resulted from an RGB to CMYK conversion:
Now when this text becomes mis-registered, you could expect the following result:
It should be noted that the negative visual effect of mis-registration is relative to the size of the graphic element. Very thick black strokes/lines, large font sizes or heavy font weights should remain legible with moderate mis-registration and could actually benefit more from being printed as a rich black.
Manual fix
By using the Quick Separations tool found in Phantasm CS or the Separations Preview system found natively within Illustrator CS4 and later, a user can switch between separation views and visually check if any of the other inks are displayed within fine strokes/lines or small size text. If this is seen to be the case, each offending object can be selected and corrected via the Color or Swatches panel.
This is a surprisingly effective technique. However, it has two major downfalls:
- It’s possible to overlook a problem, especially as these quick separations (both Phantasm CS’ nor Illustrator’s native tool) do not visually desaturate each ink for added clarity. For example, the Yellow separation can be hard to discern and is partly the reason why Phantasm CS also features the full separation tool [view video demonstration], but sadly isn’t practical as a solution for this scenario.
- Correcting more complex objects or groups which contain a mix of rich black fills and strokes would be very time-consuming and prone to human errors.
Alternative methods to detect rich black
Whereas not fixing the issue, there are two alternative methods to detect the presence of rich black directly within Illustrator. The first relies on Esko’s CheckX module from their DeskPack range of plugins for Illustrator. This preflight system works directly within Illustrator and gives two very important options to check for:
Above, the Line tabbed section of the CheckX validator parameters window allows users to determine whether strokes/lines of a set width should provide a warning if found to be constructed from more than one ink. The Font tab in the window is shown below:
Text with a composite ink color (which in the extreme would lead to rich black), an advanced option in CheckX, allows user-defined font sizes and standard or heavy font weights to be checked below a specified font size. The lower option simply warns of multi-color text which casts a much wider net to catch any potential problem.
The second suggested method to check for rich blacks is via Phantasm CS Studio and Publisher’s visual Ink Coverage tool. This tool allows levels of ink coverage to be represented in color steps very much like a weather report will display temperatures. Therefore any strokes/lines or text displayed in a color step beyond the initial range of coverage could be investigated. In the example shown below, the magenta-highlighted text to the left of the dialogue box is producing a local ink coverage of 250-320%:
This tool is great to previewing situations which can’t be checked in any other way such as text or lines which have multiple fills and/or strokes via the Appearance panel. However, a note of caution: the ink coverage level is affected by other settings such as Overprint and Transparency. For example, a perfectly defined text object defined in pure black may display as over 100% in the Ink Coverage tool as its overprinting underlying inks. Therefore the Ink Coverage method is only to be used as a guide to prompt further investigation.
Automatically fixing rich blacks
By far the easiest approach to fixing any rich black problem is to simply and automatically change rich blacks to either “pure black” (ie. just defined using any tint of only Black ink) using Phantasm CS Designer or Studio, or change rich black to any user-defined color using Phantasm CS Publisher.
The technique described here is very similar to the white overprint fix found in this previous article in the series. Once again, the advanced options in Phantasm CS is called into action and again applies to the Designer, Studio and Publisher editions.
As with removing overprint white attributes, it’s advised that the Phantasm CS Filter “Shift to Color” is used for the same reason; a 0% shift ensures no actual color change takes place while simultaneously allowing the advanced options to come into play. The tool’s Filter version is used rather than a live Effect as a permanent change is required.
Procedure:
Step 1
Select the artwork you wish to check for rich black. All object types may be adjusted, but it’s possible to target specific attributes only: Fill, Stroke, Bitmap (ie. all images) and – in Phantasm CS Publisher only – Text. This could be all the artwork in the document by opting for , and you may wish to first ensure that all layers are unlocked and therefore accessible.
Step 2
Open the Shift to Color tool by opting for in Illustrator CS3 or earlier, or in Illustrator CS4 or above.
Step 3
If not already open, display Phantasm CS’ color adjustments advanced options using the entry in the window’s pull-down menu as shown below:
Step 4
Phantasm CS Designer and Studio offer the tick option , while Phantasm CS Publisher offers [user-defined / color picker] as shown below:
The associated slider ranges from 90-100% where 100% indicates that only full rich black will be considered and 90% would consider slightly less rich blacks also. To discover Phantasm CS’ definition of what rich black is, it’s important to read this section taken from the user manual:
By default Phantasm CS determines if a color is rich black or white by examining the grayscale equivalent of the color (including RGB, CMYK and Spot colors). If a color converts to 100% Black (which can be tested by simply changing the color editing mode in Illustrator’s Color palette to Grayscale), it is considered as a pure black color. You may find that this results in lighter-than-expected colors being defined as rich black. The reason for this is that 100% Black ink printed on an offset press does not produce a deeply, truly black result, hence why it is an advantage to maintain rich black at times and why slightly lighter rich colors can be considered to be 100% Pure Black. This is also compounded by using a non-calibrated or badly calibrated monitor where colors are represented too light on-screen.
To change the definition of rich black and white to the on-screen visual appearance (ie. RGB equivalent), tick the option in the tool’s pull-down menu. This applies to all rich black and white references in Phantasm CS’ options.
The associated setting is the tick box. This ensures that only editable text – not outlined text – forms the basis of the rich black conversion process. This is the most common secondary requirement. However, if you only wish to check for rich black in strokes/lines, use the tool’s top-most attribute options by un-ticking , and, in Phantasm CS Publisher, .
Finally, click which will cause all selected artwork to be analysed for rich black occurrences and converted.
Note: when performing color changes in Illustrator using Phantasm CS such as Curves, Levels, Hue/Saturation and more, it’s possible to ensure that correctly-defined pure black attributes are not adversely affected. This can be achieved by ticking . The associated slider ranges from 1-100%. A setting of 100% will safeguard all pure blacks so that they remain unaffected by Phantasm CS color changes and do not result in unwanted rich blacks.
Automating rich black removal
As with all Phantasm CS Filters, they may be incorporated into an Illustrator Action. Simply start recording a new Action where the act of removing rich blacks as described above takes place. Replaying this will replicate the process instantly.
It’s not possible to fully describe the process of creating Illustrator Actions in this article. Therefore it’s recommended that for further information you view tutorials found across the internet or start with Adobe’s (admittedly slightly outdated, but still relevant) own page on the subject.
[...] for the issue of mis-registration on a print press – a topic discussed in the previous article, Rich black strokes and text. Here, we’ll describe methods to set objects defined with black ink only (“pure black”) to [...]