CHROMiX

How come linearity shows primaries only to a certain L

Not to the 100 L.

Thanks,
Juan

Hi Juan,

In ColorThink, in the ColorSmarts Guide, there’s a procedure for evaluating a device’s linearity. In it, ColorThink opens up a profile in the Grapher, and then changes the “Plot as…” to “points” and gives you the “primaries” point set. What this does is allow you to see how linear your primary inks are. It’s a simple spider graph showing your primaries from neutral to the maximum gamut of the profile. This is a neat little trick to see how linear your inks are - even without having to print out and measure a linearization chart. It’s all calculated from the profile.

If you are trying this with an RGB profile, you’ll get linearization primaries starting at black, and if you’re using CMYK they’ll be starting at the white point.

These spider legs should go all the way out to the widest limits of the profile. A nice way to confirm this is to bring the same profile into the Grapher again and set the opacity to 50% or less. You should be able to see the linearization lines end at the gamut boundary.

The primaries can’t possibly go anywhere near 100L because that would mean they would have even more brightness than paper white, which, of course, is simply impossible. And they can’t go to any higher L* level than what has been physically printed on the page. Think of the blue primary for an RGB printer profile and the brightest blue which can be printed might perhaps be something like 30L or 40L, depending on the paper, printer, inks and many other factors.

Hope that helps Juan.

(’:D’)