In this day and age customers expect perfection. Whether it’s the color accuracy of a photo or the perfectly straight fold of a brochure, printers are always trying to squeeze the most out of their tools. In this article I want to cover a particularly difficult area of printing; gradients.
A gradient, in regards to printing, is a smooth blend from one color to another. Gradients can come in all shapes and sizes, they can also include more than two colors. Their use has steadily increased in our industry as designers have started taking advantage of the growing number of color printers in the field. Gradients bring a set of challenges to the printer, especially in digital printing.
There are several guidelines you can follow to get the most out of your gradients. The most effective method for improving your final results starts at the design stage by adhering to some basic guidelines. Things like making sure it’s a vector element and dictating values that won’t clash with the natural dot gain from the print engine. There are also some steps you can take at the last minute to improve your results right at the print engine.
Firstly, vector gradients are far superior to raster artwork. In a nutshell, raster artwork is comprised of pixels with a defined resolution. Each individual pixel has its own color designation. A raster gradient could be described as a picture of a gradient. Vector gradients are mathematically defined. A vector gradient is essentially a line with points along its axis with color anchors. This more simple method of creating a gradient is far simpler and more forgiving once it hits the print engine. Vector gradients allow the RIP system in the print engine to do its own calculations of all the colors in between the defined anchor points. In essence it gives the printer a degree of flexibility to smoothly draw the fade based on its own math. A raster gradient comes predefined and the printer simply outputs what it receives, which isn’t always a good fit for the printer (Figure 1).
Second, we’ll talk about color limits and dot gain. This can be a deep topic but there are some simple rules to keep things simple. This part focuses on the color choices and what specific colors are used within the gradient. Simply speaking, you want to avoid having your gradient reach the limits of the color channel. That is to say, your lowest and highest color values should be within the center 80% of the full range of color (Figure 2).
When venturing outside of this safe range you are likely to experience a phenomena when printing where your gradient will have a hard step. This occurs when the color values defined in the artwork cross over the dot gain that happens during printing. Printers have a word for this, it’s called plugging. Basically what’s happening is the artwork is calling for such a high fidelity dot that it falls outside of what’s possible for the printer to reproduce (Figure 3).
Those tips are great if you have the luxury of going back to the source document. Often times, trouble doesn’t arise until crunch time when a job is due. In that situation, options are limited to changes on the output side. There are a couple things you can do to help improve your results.
Calibration is critical for smooth gradients. Calibration, or more specifically linearization, is your first line of defense when having trouble printing a gradient. A proper linearization forces the print engine’s output to be true to dot. When a machine falls out of calibration you can start to see unwanted shifts in small ranges of color. On most printers, the calibration or linearization process is rather user friendly and it’s just good practice to keep the printer calibrated.
If you’re still struggling to print a smooth gradient and your printer is well calibrated you may need to explore running at a lower line screen. Printing at a lower LPI will increase the size of the dots comprising the printed image. This can help to ease the load on the print engine and help it to produce a smoother looking gradient. It can have some adverse effects on other elements in the job but this trade off can help in some situations. If your print engine or RIP system allows, you can also experiment with alternate dot shapes, such as stochastic or a line shaped dot.
Gradients can be difficult, in many ways, they are one of the toughest elements to print. With a bit of planning ahead you can circumvent many problems by just changing some properties of the gradient. In a pinch you can also experiment with the output settings of the engine and get out of trouble.
Mid-State Litho, Inc.
5459 Fenton Rd.
Flint, MI 48507