Figure 7 shows an image converted to the same Web press space as used in Figure 6, again using perceptual and relative colorimetric renderings. In this case, the differences are more subtle, but the relative colorimetric rendering preserves more of the saturation in the water at lower left than does the perceptual rendering, without any obvious clipping of saturated colors.

Figure 7a: Original image.

Figure 7b: Converted for a Web press space using perceptual rendering.

Figure 7c: Converted for a Web press space using relative colorimetric rendering.

With vector art, unless you're trying to reproduce one specific color such as a logo, the same principles apply: If your artwork contains important out-of-gamut colors, relative colorimetric rendering may clip them to the point where they become indistinguishable from an in-gamut color with the same hue. In that case, perceptual rendering would probably produce a better result.

Application Notes
One of the many wonderful new features of Photoshop 6 is that it allows you to see how the different rendering intents will affect your image, as I described in a past column.

Some applications, notably QuarkXPress 4.x, don't offer any control over rendering intent. In this case, the profile's default rendering intent gets used. (Almost all output profiles have perceptual rendering set as the default intent.) There's little you can do about this limitation except to be aware of it, and to manage your color outside XPress wherever possible.

Other applications may use different names for the rendering intents. For example, PageMaker 6.5 calls perceptual rendering "Image," relative colorimetric rendering "Graphics," and absolute colorimetric rendering "Colorimetric." (It doesn't support saturation rendering.) Fortunately, the trend seems to be to move away from idiosyncratic naming in favor of adopting the terminology blessed by the ICC.

Different Strokes
Choosing the correct rendering intent for the job at hand is one of the essential tasks in making color management work. Look at the relative gamuts of your source and destination: The same image may need different rendering intents for different output process. For example, an image might benefit from perceptual rendering when printed to an inkjet printer, but when the same image is going out to the much larger gamut of a film recorder, relative colorimetric rendering might work much better. If an image doesn't contain any important strongly saturated colors, you'll probably get a better result using relative colorimetric rendering than you would using perceptual.

Rendering intents are simply tools. It's up to you to use them. If you take the trouble to understand what they do and then use them wisely, you'll produce better color than if you simply accept the default settings of this or that application.

Read more by Bruce Fraser.