Introduction: Color management engines will often "contaminate" a pure black with other colors in an attempt to get the black hue of the printer to match the black hue of the target CMYK color space. This is usually desirable. It can lead to darker blacks and it is generally one of the points of color management. However, this can cause problems with text or hairline rules. These objects can look hazy or fuzzy due to slight misregistrations between colors. Some of the under colors can leak out and cause the edges to be less defined.
A built in partial solution: Navigator has a toggle to "preserve 100% black" or "print 100% black with only black ink". This stops the color management engine from adding other colorants to the black when that black is 100%.
For offset printers using color management for proofing this is an adequate amount of control.
The problem defined:
On a digital press with color management "preserve 100% black" may not be enough control.
We have encountered a category of jobs which have grey scale text. (e.g. A bank statement from a particular bank has the entire back page of most sheets as screened black text.) These jobs print with the text as a 4 color mixture due to the color management engine. It varies from average quality to unreadable within a print run.
Any job with this exact problem which is entirely black you could just print with color management off.
When the color management engine is required for other elements in the job it becomes more complicated.
We have created three page features (enabled in a RIP Page Setup) that will address this problem in three different ways. Each of the page features acts only on channels which are presented to the color management engine as pure grey or black.
1. "Pure Grey+Black". Bypasses color management for text and line art between 0% - 100% black.
2. "Pure Grey+Black text". Bypasses color management for text between 0% - 100% black.
3. "Pure Grey+Black lineart". Bypasses color management for line art between 0% - 100% black
To install a page feature just drop the file into the folder inside the Navigator RIP folder at sw/page features/.
How to decide which page feature to use:
If you are uncertain about which way to proceed, there is a test file included in the delivery (attached to this article) called "preserve black test.pdf" which will help you to see the effect each page feature will have.
You can use these page features in conjunction with the "preserve 100% black" checkbox to achieve different effects.
For example: If you wish to print all grey or black text and 100% black line art only on the black channel, check "preserve 100% black" and use the "Pure Grey+Black text" page feature.
Warning and suggestions:
Should you use this? If you are trying to fix a problem caused by improper file design, we suggest you encourage file designers to do their job properly. Turning off color management for one color may have undesirable side effects.
The "pure grey+black" effect could also be achieved using the "pure primaries" feature of an ICC profiling application. This requires the use of device link profiles which should be studied for applicability to your situation.