CHROMiX

UCR or GCR for Inkjet

again its me … :wink:

pretty much the only one here latels… im sorry…

im just reading a lot and trying different things…

everywhere its said to use a strong GCR when building a RIP CMYK profile for inkjet printers.

but from my understanding. isnt it smarter to use UCR if the inkjet has 4 grays so i Want it to use the K inks from 0 on… ??

UCR (Under Color Removal) is basically a “light” version of GCR (Gray Component Replacement) and it’s useful not only because it saves ink (and therefore money), but also because it can make a printer more stable in some of the tones that tend to be the most unstable. There is more information in an article that Steve Upton wrote awhile back:
colorwiki.com/wiki/The_Color_Key

Traditionally, you don’t want to start your black right off at 0 as the black ink will show up as speckling in the highlight areas. For this reason the user will allow CMY inks to build the highlight tones and start in with the black ink for the portions of the print that are darker. In your situation, if your inkjet has four grays than it might very well be that you could start at 0 with a light light gray and this would produce no more speckling than the CMY inks. That’s pretty much the whole purpose of having those light grays.

But you always have to do some experimenting as your mileage may vary. The subject matter, how close the print is expected to be viewed, all factor into this as well.

Keep asking questions. We like them!

thanks patrick…

yes… i read this article before… and many others… and thats WHY i came to this conclusion…

i have gotten the feeling that everything we can read is not really up to date anymore… or at least doesnt include todays “machinery”…

everyone!! tells me use a strong gcr… and start your black at 40… because of the black dots…

but the new machines (hp now for 6 years!!) have llg! using smaller dots than black, like light inks… so i dont even want any cmy in my gray axis…

a lot of testing… as you say :wink:

the interesting thing is… with onyx f.e. even if i use UCR… and put 0 min and 0 max… meaning actually no K should be substituted… at around 40 it starts to add CMY to my K… and till that my grayachsis is totally stable…

It sounds to me like you’re on the right track with what you’re aiming for.

A little known fact is that the carbon they use to make black ink is not perfectly neutral. At least, when they ground it as fine as they need to for inkjet inks, it starts to go brown. So RIPs would expect to add CMY into a black ramp at a certain point. Now, they may have solved this problem with more modern ink sets - but I wouldn’t be surprised if ONYX still starts a little bit of CMY early on in its algorithms as you see.

This is probably one of those things that should not be, but are. Right up there with why a strong red build includes a small amount of cyan ink. And how come glue doesn’t stick to the inside of the bottle? And who created the word “Lisp” to have an “s” in it? I dunno. Some things in life are just wrong. :wink:

thanks patrick for the great conversation!

i just realize that many people just stick to the old stigma better to call stiCKma… haha… you cant do good fineArt prints without a RIP…
the drivers are so advanced nowadays that its hardly impossible to get better results… then if you finally get a 5% bigger gamut the rasterization is not as brilliant as the internal one… and so on…

im just coming up with another question… i see that i can reach a L value of 15 on a matte paper with pure black printing (lin)… in the profile i only get 18 as my lowest… probably because it is using CMY+K for that…

which trigger can i pull to get a deeper black?–i dont see how i can prevent him for using CMY in the blacks… using onyx right now

That is a mystery. If your linearization print puts out a K only black at L value = 15, you should be able to get close to that when you print through a profile you make using that linearization. Here are a few ideas:

  • Are you sure that is the linearization you used when you made profile?
  • Did you put in some additional ink limiting into the profile itself? That would reduce the gamut of the profile.
  • Which rendering intent are you using? Perceptual can bring the black point up higher.

hi patrick.

indeed i can see that pure black has L of 15.7 … the profile with rel has 17.5 and with perc even 17.4

and i can see that the profile adds cyan and meganta… so it could be that onyx sacrifices the lower L for a neutrality…?.

its all done within onyx. so i dont see where i could miss using the lin… and the profile and prints look good afterwards… maybe i could change somethin in the black generation again… hmm