Fluid Fountain Fills

A frequent occurrence with fountain fills, using a CMYK color model, is that gradients from black to a color (or custom gradients when a transition from black to a color is used) appear “washed out” in the mid ranges when outputting to either a CMYK color output device, or when creating CMYK separations. In this article, we’ll discuss why this happens and how to avoid it.

The Problem:

The “Normal” Gradient

When creating a gradient from black to a color, using a CMYK color model, most often the user will indicate 100% black on one end and whatever the color is for the other end. In the example shown here (Figure 1), the gradient changes from 100% Black to 100% each of Cyan and Yellow, to make a 100% green.

These particular colors (black and green) may easily be specified from the provided color palette with your gradient tool, but if you examine the actual CMYK components of the black end of the gradient, you’ll find there is neither a Cyan nor Yellow component at all. You will see, shortly, why this is important.

Figure 1. The “normal” gradient

Behind the Scenes

The reason this gradient looks fine on your monitor is that your monitor doesn’t know beans about CMYK-all it can do is display in RGB (Red, Green, and Blue). The black end of the gradient is the absence of all three RGB components, and, to achieve the green, the Green component is gradually added to the fill. For more information on RGB color, see the Color Primer.

For the same reason, this gradient will appear just fine when output to a CMY output device (one that mixes Cyan, Magenta, and Yellow to achieve a black color.

Why the CMYK Fill Fails

However, when output to a CMYK device, or when creating separations, a true black component is used for the black end of the gradient, and it is gradually decreased across the span of the fountain fill. As a result, in the middle of that span, the black component is reduced to 50% black (see Figure 2).

Figure 2. The Black component is reduced to 50% at the midpoint of the gradient.

At the same time, the Cyan and Yellow components are gradually increased, from 0%, to the final percentage (100%), and they, in the middle of the gradient, are also at 50% (see Figure 3).

Figure 3. The Cyan and Yellow components are also reduced to 50% at the midpoint of the gradient.

So what you end up with, in the middle of the gradient, is 50% Black, and 50% each of Cyan and Yellow. If you want to see how this will look, just create an object and fill it with those color specifications (50% each of Black, Cyan, and Yellow) and you’ll see that this does not create a darkened version of the solid green.

The Solution

To get a truly darkened green (to match what your monitor is showing you, at least, as well as can be expected) so that it will output correctly, either to a CMYK color device or for separations, you need to specify the same percentage of Cyan and Yellow components for the Black end of the fountain fill.

Figure 4. On the left, above, is an approximation of CMYK output of the “normal” gradient (no CY component at black end). Note the muddy green color at the midpoint. On the right, above, is an approximation of CMYK output with the full component of color at the black end.

When specifying the black end of the fountain fill in this fashion, the midpoint of the gradient will now contain a different mix of colors from the “normal” gradient-the midpoint will be a mix of 50% Black, 100% Cyan, and 100% Yellow, providing a solid green color with the Black component added to it (see Figure 4).

Recap

The key in specifying black-to-color gradients (or gray to color, for that matter) for CMYK color output or CMYK separations is to include the full value of the color end of your fountain fill in the black end, to provide a full saturation of color along the full span of the gradient.