Mastering digital printing can be challenging. Getting it right requires learning about color gamuts, ICC profiles, and the features of your particular printers, cutters, and software. Some of these are pretty obvious, like choosing the right media and using the right ICC profiles. Some are a little trickier. Even when you’re doing everything right, There is one setting that can cause serious color management issues. Getting this setting wrong can cause frustration, work delays, and at worst, lost customers. Fortunately it’s also easy to fix. We’re talking about rendering intents. What are rendering intents and how do they effect color management?
What are Rendering Intents?
Simply put, Rendering intents are settings used to help your RIP software manage the transition from one color space to another. Your monitor works in RGB, which is an additive color space based on light. Your printer works in CMYK, which is a subtractive color space based on ink and reflected light. More info here. Your RIP software manages the transition from the RGB gamut, which is very broad, to the narrower CMYK gamut. Part of the RIP software’s job is to decide what to do with the colors that exist in RGB, but not in CMYK. These are known as ‘out of gamut’ colors. This is the function of rendering intents.
Raster, Vector, Text, or Gradient?
Raster and vector image files must be handled differently by your RIP software. They require different rendering intents. Using rendering intents optimized for raster images may produce unsatisfactory results with vector graphics and vice versa. There are also rendering intents best suited for printing images with text and vector images with gradient fills. So the first thing to ask yourself when you’re trying to solve a color management problem is, what kind of file am I printing? Is it a raster image, a vector graphic, text, vector with gradients, or some combination of these?
Perceptual, Relative Colorimetric, Absolute Colorimetric, and Saturation
There are several different rendering intents used in RIP software. Deciding which to use might seem confusing, but it’s less challenging than you might think. Each one manages out-of-gamut colors differently. The differences in how they manage out-of-gamut colors can have different impacts on overall color management. Selecting the right rendering intent for a print job may also depend on your goals. You may choose one over another based on whether your goal is color accuracy or vivid color.
So if you know which kind of graphic you’re printing, and what your goals are, selecting the best rendering intent is much easier. Here’s a summary of the rendering intents used in Flexi software. This guide is from SAI’s FlexiHelp knowledge base. So if you’ve been doing your homework, it may look familiar.
- Perceptual: Colors outside of the output device's gamut are compressed to fit the output device's color space. This intent is best for photographic images.
- Relative Colorimetric: Colors that fall outside of the output device's gamut are clipped. The white point of Relative Colorimetric is always zero. This intent is best for images (such as logos) where the output needs to match the original image.
- Absolute Colorimetric: This intent is similar to Relative Colorimetric, but it has a different white point value. Absolute Colorimetric represents colors relative to a fixed white point value of D50. For example, the white of paper A will be simulated when printing on paper B. This intent is best for color proofing. This option is best suited to use on media with a high white point.
- Saturation: Colors outside of the output device's gamut are mapped to colors at the extent of the gamut's saturation. Colors that fall within the gamut of the output device are shifted closer to the gamut's saturation extent. Saturation is best for graphic images (such as vector art) where vivid colors are more important than true color matching.
What happens when they’re wrong?
Now that we know what rendering intents are and how to use them, the next important question is how do you know when they’re wrong. Well, that part’s pretty easy. If the rendering intents are incorrect, you can use the right ICC profile with the right media and your colors will be ‘off’. They may look too dark, too muddy, or just wrong. The most common indicator of incorrect setting here is muted, washed out color. Sometimes the print just looks too dark. In the example below, one of our test prints we use to verify new ICC profiles came out looking much too dark. The colors were muted and the black channel was overpowering the rest of the gamut. We checked the rendering intent and changed it from Relative colorimetric to Perceptual and everything popped back into place (FIG 1).
Setting Good Rendering Intents
Rather than fixing color issues after printing, the best way to manage rendering intents is to make this part of your RIP & Print process. In Flexi Sign & Print and LXI RIP Design software, rendering intents can be set in the RIP & PRINT window or in Production Manager.
Working from the RIP & PRINT window make sense because the software will read the design and offer rendering intent settings for the elements detected. In the RIP & PRINT window, click the ‘advanced options tab (third from left). Then click the ‘color settings’ button at the top right to open the Color Settings window. Here you will see rendering intent options for all the elements in your design. If your chosen rendering intents in the RIP & PRINT window don't match the Default Job Properties set in Production Manager, you will be alerted to this with a window labeled "Color Setting Difference" and asked which set to apply to the job (FIG 2).
Speaking of Production Manager, you can also set rendering intents here using the Job Properties or Default Job Properties options. The best method is to set your default job properties to the recommended settings listed above. Here’s how to set good Rendering Intents parameters in Flexi or LXI RIP software.
- Open Production Manager and right-click the printer device setup. From the drop-down menu, click Default Job Properties
- Click the Color Management tab (third from the left) to open the Color Management Window.
- Click the Advanced button midway down the window to open the Advanced Color Management window.
- Click the Rendering Intents tab (center) to open the Rendering Intents Window.
- In the CMYK column, you will see Bitmap, Vector, Text, and Gradient. Click the arrows at the right side of each window to open the drop-down menu and select the best option for the type (FIG3).
- When you’re done, click OK in the Advanced Color Management window, then click APPLY at the lower right corner of the Default Job Properties window to save the settings.
Fixing Color Shifts in Complex Graphics
Setting good default settings for your rendering intents will prevent most issues and produce good, consistent color. If you have files with a combination of raster and vector elements, your settings may need to be adjusted to handle random color shifts. In Fig 4 below, we have a design that includes a raster image, a vector border, and text over a shape with a gradient fill. We’ve checked all the boxes. The image on the right shows what happens when one of the settings is off.
Wrapping your mind around rendering intents and their intended targets may sound confusing or intimidating, but it’s really not. Setting good defaults makes most of these issues go away. But when they arise, just remember the old adage, ‘garbage in, garbage out’. Focus on the type of graphic elements in your design, keep your goals in mind, and set the rendering intents accordingly. Of course, you want to make sure you’re using the right ICC profile for your printer, ink, and media. But, if all of that looks correct, but your color doesn’t, fixing your rendering intents is usually an easy solution.