Defining Black - getting the best possible black

Poor blacks have to be the most common file preparation mistake I see. I don’t think a day goes by without having to fix how black is defined in the files I see. Even when a “process” black has been set, it is often not as dark or as neutral grey as it should be. Defining black in your files, whether they are RGB or CMYK is simple once you understand how the computer (and our print systems) think of black.

The most common mistake is to set black as 100% black in a CMYK file. I know it sounds funny, but 100% black is actually very weak and not nearly as dark as it can be. In RGB files it is simple, set red, green, and blue to all zero and voila! you’ve got a proper rich black. So, this post will deal with setting black in CMYK files.

To understand how the computer thinks of color, it helps to realize that all digital color, whether it is CMYK , RGB, or Pantone, is referenced to another color space behind the scenes; LAB color space. LAB is modeled after the range of color we as humans are capable of seeing. In the digital process, it is used as a common reference for color so we can make our conversions from RGB to CMYK for example. We also use LAB to move color from one step in the workflow to the next accurately with ICC profiles. The ICC profiles used within design applications to store color are referred to as Working Spaces. The most common CMYK working space in the America is US Web Coated SWOP. Unless you’ve made special effort to change your working spaces (which I generally don’t recommend) and you are in the US, you’re using US Web Coated SWOP.

LAB breaks color into 3 axis, L for lightness, with A and B defining hue and saturation. Since we’re focusing on black here, lets simplify the discussion to lightness and the knowledge that perfect neutral grey will have a zero A and zero B value.

Black defined as 100% K

We’ll use Photoshop’s color picker to see how black translates through CMYK, RGB, and LAB all at the same time. Look at how 100% K translates as a LAB value in the picture. Perfect black in LAB would be L=0, a=0, b=0. Note how L is much higher than zero and the translation to RGB values are all higher than R=0, G=0, and B=0 when black is set as 100% K in CMYK. When black is defined this way, and we do our job of printing the color in your file accurately, you’ll get a very weak black. Also note how the A value in LAB is not zero. This means the black is not only weak, but it also has a color tint that takes it away from being perfect grey.

Perfect process black

The common solution is to define a “rich” or “process” black. This means adding some CMY to the 100% K to make sure you’re getting loads of ink on there. Sometimes I see overkill mixes like C=100, M=100, Y=100, K=100. Instead of going with some mythological mix that’s been passed down through designer to designer and from prepress operator to prepress operator, let’s look at how the computer thinks of a perfectly neutral rich, process black in the next picture. Note how the balance of CMY is not even numbers. Setting black as something like C=50, M=50, Y=50, K=100 will actually give a black that is dark, but not neutral grey. If the printed version of this is dark enough, you may not see the error. But in bright outdoor light, you are likely to see it. Also, if a gradient is made from this non-neutral black, you’ll get a funky color shift through the gradient.

Practical Solutions

When you are selecting black in Photoshop, simply set LAB or RGB to all zeros so you don’t have to remember the specific CMYK mix that gets the best black. By default, Photoshop will display black accurately on screen. That is to say 100% K will look lighter on screen than a proper rich black. Illustrator is not set this way be default and needs to have its setting changed.

Black Preferences in Illustrator

By default, Illustrator is set to show all black on screen as if they are rich blacks, whether they are 100% K or a proper rich black. This is particularly evil since it is very common to set black manually in Illustrator. Change this setting within the Preferences and make sure all your colleagues do the same. Set it to “Display All Blacks Accurately” for screen and print/exporting. Be careful not to use the default black in the color pallet since it is simply 100% K. In Illustrator, you can change the color picker to be RGB or CMYK regardless of the file’s color format. In other words, you can have a CMYK file, but select black in the color picker as R=0, G=0, B=0. Then switch the color picker back to CMYK to see the proper rich black values.

On the print side, we take great care to ensure that our blacks print as dark and as neutral as possible 0n every material we use. Our custom color managed systems automatically take care of any fancy GCR (replacing CMY with extra K) that is needed for each type of material. This is one of the many things we craft into our systems to give you the best possible output day after day.