limiting black ink density


im new to this forum and this is my second topic appreciate your help.
i have question regarding separate ink limit .
i am measuring the density chart and exporting it as txt and opening it in Colorthink pro using Lch values along with the spider graph i can see where each channel is starting to drop and limiting the density to the max. thats for colors. As for black, what should i do? how can I determine the maximum density?
is it true that black density value should always be bigger than CMYRGB channels?

thanks !

When you’re checking out a linearization target measurement in a 3D program like ColorThink, the different ramps of color look like the legs of a spider. …

As you say you can visually see where to cut off your ink limiting with the different colors, but the black ramp as it heads darker is not quite so obvious. For some measurements, if you look closely, you may see where the black actually gets lighter with more ink. This can be due to bronzing or pooling of ink when there is an excess. You’d have to look closely and follow each ink patch (like I demonstrate in the video above); you can’t just look at a spider graph and assume that each point is laid out in order to the darkest. Obviously, you’d want to cut off your ink where you get the darkest point, and before it starts to get lighter. On some systems, the black line start to curve like a corkscrew around the neutral axis. To have a stable printing workflow, you would want to cut off the black ink before it screws around like that.

These two scenarios are not too common nowadays. If you have a well behaved inkset and printer and it just steps down to the darkest black it can hit, then call it good. The viewing of linearization ramps in a 3D graphers is perhaps more useful for the colored ramps than for black. It all depends on what your purposes are too. If you want the most gamut, you can allow more ink. If you instead want a press that has more stable color or want to save ink, you can limit the ink more.

Regarding your second question,
There will be a black patch made up of 100% K ink only, and there are black patches made up of CMYRGB and K ink. These rich black patches will generally be darker (have more density). It’s hard to say "never’ but I don’t think I’ve ever seen a system where the CMYRGB without K ink patch was darker than 100% K.

hello patrick,

thanks a lot for your reply.
this is what exactly i am doing on color think pro. as for black i will try it now.
the problem is that i am checking the highest chroma on CT and limiting the channel as it says but when i print a Total ink limit chart i get bleeding always on cyan chart and the dark charts.
and the more i try to reduce the more i get a low gamut profile. ( this happens mostly on innova and BC canvas)
so a small gamut profile doesnt help me in fine art reproduction.

hope this helps.

That’s a tough spot to be in. But at least you’re not alone! Printers often have a hard time getting good gamut on difficult media.

What you might do is choose a linearization setting that only gives you a little bit of bleeding, and then make two profiles for this media: One for wide gamut with no ink limiting and another for a more low gamut profile where you constrain the total ink limiting inside the profile itself so that there is no bleeding.

Since you have ColorThink, you can bring your actual images into the Grapher and make decisions image by image which profile to use. It might be that many of your fine art images will be able to get by with the lower gamut profile, that the particular colors in one image fall with the smaller gamut boundaries. Since you have the Grapher, you can see exactly where each pixel will move to when converted to the profile. And you will be able to use the wide gamut profile on certain images that don’t have a lot of dark shadows? I don’t know. I suppose it doesn’t sound very hopeful, but I find that in actual practice you can get away with more than you do when printing a page of profiling patches.