We all know that web presses (presses that print magazines and newspapers) run in CMYK plates, as opposed to RGB like your local Kinko’s would. Normally we create our design files in CMYK, whether in Photoshop, InDesign or Illustrator. It’s almost automatic. But sometimes we all receive the occasional “camera-ready” illustration or ad file that needs to be converted to CMYK. And sometimes this process produces blackbuilds or rich blacks. So let’s try to understand the difference between the two and why/when it is important to use one or the other.
First of all, CMYK is composed of four plates, or process colors. Cyan (C), Magenta (M), Yellow (Y), and Black (K). Standard process black is 100%K, or 0/0/0/100. Visually, 100% Black is a kind of washed-out black, not a deep black like we can obtain through rich black. Rich black combines ink from all four plates to produce a dark, super-saturated black. An example is below, which uses 70/82/90/100.
Rich blacks can be very useful when looking to obtain a deep, dark black over a large field of solid color. However, be aware that utilizing rich blacks can have two negative effects:
1. Super-saturation. Depending on your medium, this can be a real problem. If you are designing for newsprint, using inks in excess of 240% can cause the ink to soak through the page and obscure content on the other side. In the above example of rich black, we would be using ink percentages of 342%. Check with your printer to see what their maximum ink limit is for the medium you are using. You can check overprints in Adobe Acrobats “Output Previewer” option (more on that later).
2. Registration problems. This is the most common dilemma caused by rich blacks. Sometimes the registration, or alignment of the different color plates will be just a fraction misaligned. This is normal, especially for newspaper printing. However, when utilizing all four plates to create black, especially text or knock-out text, the margin for error is minimal and misaligned plates can cause illegible text.
Below is an example of using 100%K text compared to rich black text:
And here is an example of knockout white space in a field of 100%K as compared to a field of rich black:
As you can see, rich blacks should not be used on black fields with knockouts, or on text under 48 pt. Using these general guidelines will hopefully help you avoid ugly or illegible text.
So what happens when you receive camera-ready artwork that needs to be converted to CMYK from RGB?
This can be a frustrating process. But it’s really quite simple. When converting an image file or PDF to CMYK in Photoshop, it generally defaults to CMYK profile US Web Coated (SWOP) v2. However, as illustrated below in the channels window for our camera-ready ad, this profile creates blacks built with color in all four channels. No bueno.
The key is creating a custom CMYK conversion profile that limits the black ink to 100%, and generates the maximum amount of K for blacks. To do this, we will go to Edit>Color Settings…>CMYK dropdown menu>Custom CMYK…
This produces the following screen:
Here we will select GCR, Black Ink Generation = Maximum, and Black Ink Limit = 100%. Click OK. This will save your custom CMYK profile. Exit the Color Settings window and return to your RGB image waiting to be converted. Now we will convert to CMYK by selecting Image>Mode>CMYK like we always do. But this time it will load the custom profile you just made, and presto! Look in your channels window and you will see that ll the black is in the black channel.
Also note that an easy way to check for built/rich blacks in a camera-ready PDF is to utilize Adobe’ Output Previewer. In Acrobat Professional, go to Advanced>Print Production>Output Previewer. Not only will this break down the ink builds when you hover the mouse over colors on the page, but it will highlight rich blacks and overprints for you. This is a very useful tool when preflighting your print files.
I hope this brief tutorial is helpful. If you have any questions, feel free to ask!