Restriction by Chroma vs Total Ink Limit

[neil_se]

I've been on a profiling journey since installed Caldera last week. I've read some helpful info on here today about restricting by measuring chroma which is simple enough in Easy Media. The result however of using peak chroma is that the necessary ink limit breaks Caldera's suggested rule that the ink limit should not be less twice the average individual limit (/half the sum of the limits). At the total ink limit that meets this rule the result shows heavy coalescing and bleeding. Eg. peak chroma for my Roland XC540 on monomeric SAV (720VD, 8 pass+ RIPC) occurred at 70/85/90/75% Pmax, but total ink limit should really have been around 140%.

Originally I was just limiting by eye, but when I did carry through the whole process using peak chroma the gains in estimated gamut reproduction were fairly significant. But of course the profile wasn't much good in terms of pooling and bleeding.

Qn 1. Is there a method/measure/rule of thumb I should be using for picking restrictions, or do I need to go to the extent of downloading Profilemaker and measuring back ~1 deltaE from the peak?

Qn 2. So far I've just been using the bleeding target after setting total ink limits, but are there other useful targets I should be using during the process?

Qn 3. Do others just leave Easy Media's suggested light ink transitions, or do you reduce them back knowing that you'll likely be restricting channels in the linearisation?

 

[P Wagner]

Light inks (light cyan and light magenta) do virtually nothing to enhance the gamut volume, but they do tend to put a lot of the ink's base (water or solvent) onto the media, which needs to be controlled through heat or other means. Particularly with the latex inks but also solvent, you want to be very aggressive in limiting the light ink channels.

Also, I don't like to limit total ink/ Total Area Coverage below 200 percent, as this reduces your gamut for secondary 2-color mixes (red, blue, green).

 

[neil_se]

In Caldera the total ink limit is expressed in terms of printer output capacity, so if the channels were restricted to 80/80/80/80 then the maximum would be 320% and I'd be looking for a total ink limit of at least 160%.

 

[a77]

Hi Neil,
I'm new to Caldera and sometimes struggling with easymedia with setting ink limits.
To be honest I often end up printing the profile target and then noticing some bleeding between patches or some coalescence. I find it most useful because it shows so many colour combinations.

Then I am faced with the same problem.. I want to reduce my ink limit so low that I am going below the magic [Pmax average *2] number. So then I go back to setup new linearization curves by using my previous readings and just sacrificing my Pmax's to come up with something close to make my restrictive ink limit work.

I am only CMYK, so I don't have to work with light inks, so I guess that's one less step to worry about. But still, I'm not terribly happy with the process and don't have much confidence in some of my choices. For me, with my epson surecolor, I am most worried about ink drying times so that I'm confident I can go through to the takeup reel and not be worried with heavy coverage jobs. So I'm playing quite the guessing game by watching the test target and seeing how quickly it dries, trying to get away with as much ink as possible.

Sorry, no useful info for you, more of a rant, but I am interested in any other tips/tricks or best practices for handling these limits so if anyone else has much experience with this, please chime in!

 

[rfulford]

Honestly, It sounds as if your media and print mode do not want to cooperate. This is not really surprising for a monomeric vinyl. Most that I have run across are really cheap. Is this the case? It sounds like you are doing everything right but the values you are picking sound way too low for a reasonable ink restriction. If you must use this media, you may have to go to a higher pass mode or drop your restrictions to account for where you need to set your ink limit. Also, you can try to keep them where they are, and continue with the profiling process realizing that you will not be able to produce works of art on this particular vinyl. This will not be a surprise to anyone. The danger in using a ink limit that is too low is that you will not be able to accurately mix C, M, and Y to approximate gray and your GCR will cause posterizaton in your shadow areas. You want to use GCR 4 or Max Black when dealing with low ink limits but still, your results will be marginal.

 

[a77]

Funny, I've been having these problems with almost all media..

That is a good tip to print a test target that has some greys to see how it looks with the ink limits. But I suppose this test really is only accurate after you've gone through all the steps to create the profile.

 

[neil_se]

I haven't had a great deal of time for experimenting in the past fortnight, but does anyone have ideas on if or how the hue shift should be taken into account in the individual restrictions? Eg. in the linearisation below, max chroma occurs and the 83%, but there's a large hue shift past 60%.



Is it useful or useless to include this area from 60 and 83% in my restrictions?

 

[P Wagner]

I haven't had a great deal of time for experimenting in the past fortnight, but does anyone have ideas on if or how the hue shift should be taken into account in the individual restrictions? Eg. in the linearisation below, max chroma occurs and the 83%, but there's a large hue shift past 60%.

View attachment 94423

Is it useful or useless to include this area from 60 and 83% in my restrictions?

You should be restricting (Cyan in this case) at point where the hook (direction change) occurs.

 

[neil_se]

Cheers, that's what I ended up doing as the bleed test showed cyan was too heavy. I figured that the shift wasn't adding significantly to gamut anyway.

 

[a77]

Neil,
Which version of caldera are you using?

Just got this reply a few days ago from Caldera:

"That rule doesn't apply anymore to the latest i1Profiler we're currently using. It will be removed from the next version of our manual.

The only effect of limiting your primaries in order to follow this rule now would be to restrict the gamut - sometimes just significantly, sometimes considerably."

Kind of ridiculous since that is the only real essential bit of info in the EasyMedia manual....
Well I'll be reprofiling a lot as I was trying to satisfy this rule and making compromises when making decisions while profiling.

 

[neil_se]

Mine was the latest version from around the date I started this thread. It's interesting that they now say to ignore that when it's repeated at least 3 or 4 times in the manual. The experienced colour management tech who did my install also said the same (but he dumbed down a lot of info for me since we had such a rushed timeline too).

I might have a play with it during the Christmas break.