June 19, 2010

Understanding How Rendering Intents Work

Filed under: Uncategorized — admin @ 3:37 pm

Rendering Intents are, essentially, the logic used in remapping color into a smaller color space. The two basic rendering intents that we are dealing with are Perceptual and Relative Colorimetric.

Perceptual intent presumes that you want to keep the relationships between all the colors, that is, if you have colors that appear different, we want to keep that appearance when they are remapped. Converting colors with Perceptual Intent requires that we move all the colors in the space around a bit. I like to make an analogy to a sponge, or a balloon. Perceptual intent kind of squishes the sponge up, and the entire sponge changes shape a little.

Relative Colorimetric intent is more of a cookie-cutter effect. If colors are outside of the smaller space they are moved to the closest color inside the space. All the colors inside the space remain untouched. If, in the conversion, the colors being remapped lose their relationship to each other, that is, lose their “spacing”, well, so be it.

Here are some examples. I went back to our color burple, and made a couple of other colors… blue, burple and purple. Here they are, sitting well outside the Epson Premuim Luster color gamut (shown very lightly shaded).

The next illustration shows the three colors mapped into the gamut of Premium Luster using Perceptual Intent. You can see that the distances between the three are almost exactly the same, and they’ve been moved around a little. This is to maintain our perception of them, and their relationship to each other.

The final illustration shows the same colors mapped in using Relative Colorimetric Intent. As you can see, they are closer together, they are mapped directly into the gamut just to the nearest available color, with little concern for maintaining any relationship between them.

So when do you use which one? Keep in mind that with Perceptual Intent everything gets changed… Relative Colorimetric, only the colors that need to change get changed. There’s your answer.

You use Perceptual Intent when you need to make some big changes in your gamut, and the “look” of the colors is important. For example, if you have a full, rich blue and purple image and you are printing it to Premium Luster you may want to use Perceptual Intent so that the colors will print with the same differences and “spacing” you’re seeing in AdobeRGB, but get mapped into the colors that the printer can work with.

Relative Colorimetric Intent is really handy when, for the most part, all of your colors are inside the printer gamut, and only a few, like our burple, aren’t playing nice. We don’t need to push everything around just to get burple in there, we just need to push it in, and leave everything pretty much as it sits.

This is a great case of, if you know where your colors fall, and you know what your gamut is, you can make the best choice about how the system is going to convert the colors and keep as much of the image intact.

(Excerpt from Color Pipeline- courtesy of Ted Dillard -Lark Books)

Powered by WordPress