RGB to CMYK and total ink limit

[jstotz]

If I build a profile and specify a total ink limit of 300%, is there anything other than that setting that effects the ink limit? In other words, if I used that profile to convert an RGB color of 0,0,0, to CMYK, why would the CMYK build be 100,33,21,100 with a ink limit of only 253?

[TerryWyse]

If I build a profile and specify a total ink limit of 300%, is there anything other than that setting that effects the ink limit? In other words, if I used that profile to convert an RGB color of 0,0,0, to CMYK, why would the CMYK build be 100,33,21,100 with a ink limit of only 253?

With those numbers, sounds like an inkjet printer.

A lot depends on the profiling application you're using.....it's not uncommon for a profiling application to alter the total ink limit you requested, especially in the case where you request a total ink limit that is too high to maintain good tonality (shadow detail) or good neutral balance at the total ink limit. Another factor could be the type of K generation you request....UCR, GCR, the amount/% of GCR you request, etc.

In your case, it's quite obvious that the device you're profiling has strange gray balance numbers so it appears that 253% is the maximum amount of ink that can be laid down and still maintain gray balance....if the magenta and yellow were raised any higher, the profile is basically telling you that this maximum black would result in a color cast.

Terry

[TerryWyse]

...I'lll elaborate a bit more....

i'm guessing an Epson Ultrachrome inkjet printer, correct?

If so, Ultrachrome Photo Black ink tends to be very "warm" or yellow-ish/brown-ish looking, as if the ink is lacking cyan.

What you are likely seeing in those total ink numbers is the result of this too-warm black ink that is requiring a maximum amount of cyan ink and reduction in the magenta/yellow inks.....the K ink is basically contributing it's own magenta/yellow color cast thus requiring an increase in the cyan and reduction of pure magenta/yellow. If my guess is correct, this is actually perfectly normal and expected. HOWEVER, such a gross imbalance of ink % at Dmax could be an indication of incorrect per-channel ink limits in the case of an inkjet printer or grossly incorrect solid ink densities in the case of a press.

Terry

[Lukas Engqvist]

The thing is that more ink isn't always going to give you the darkest colour. So the maximum ink isn't necessarily at RGB 000, also (as with speed limits) there may be other reasons why you don't want to stay at maximum

[jstotz]

The data file is from an IT8 for a UV press, dry trap, on uncoated paper. I hadn't thought about the need to maintain gray balance, but that makes perfect sense. You can't print 110% cyan.

I checked the data file. The 100,100,100,100 patch is 23.2L, -.7a, 2.3b and the 100,100,100,0 patch is 28.3L, -.4a, 3.0b. I think it's the dry trap that warms up the dark colors.

Thanks,

[rich apollo]

I think it's the dry trap that warms up the dark colors.

Yep. Interstation drying should put your ink trap numbers well above 90%. That's gonna' leave A LOT more M and Y on the sheet than traditional offset, and cyan is our weakest color link to begin with. Are your blues quite "purply" and your greens rather "yellow-ish"?

With the numbers you posted, where does the darkest color reading in your IT8 occur? You may be able to cheat the profiling software, but be warned, you'll probably induce something that looks kinda' like "bronzing" on an inkjet.

[jstotz]

My trap numbers are:
M/C 77%
Y/C 92%
Y/M 52%

The darkest color is 100,0,0,100 at 21.35L -1.74a -8.27b

100,100,100,100 is 23.16L -0.68a 2.28b

[rich apollo]

My trap numbers are:
M/C 77%
Y/C 92%
Y/M 52%

Really!? I think something is wrong with the ink transfer on the magenta unit. I can do better than your blue and red overprints on an offset web press. 52% on your red overprint is waaaaay low. In a non-UV environment that should be upwards of 70%