Color Cast & Weird Neutral Rendering Curve in ColorThink

Running a linerization and profile on epson 9600 from Colorburst RIP SpectralVision- ie same as Xrite profiling. Lin looked good with reasonable step values (and values for c,m,y, and k suggested by colorburst).

Built a profile - profile target prints looked good- generation seem to go ok but the profile produces clogged black and an overal magenta cast from about mid-tone. Printer is remote so it is not that easy to run lins and targets over and over. I looked at the neutral rendering curve in ColorThink and was perplexed. here it is:

First- if anyone can intrepret this rendering curve - with its wacky lines- I would appreciate a heads up.

I am at a overall ink limit of 250 with black at 50%. I am thinking that the amount of magenta ink is just too much relative to the other inks and I should reduce the limit on the individual magenta channel and maybe step up the black (if it can take the ink). (Notice black is at a max density at about a 3/4 tone.) Then relin and re profile.

FYI- the black started at 25 either by default or my selection.

Anyone with hints or suggestions - I welcome them. Thanks

That certainly is a strange one. Especially with the magenta reversing itself like that - I wonder how the blacks can possibly be neutral? I would think it would produce rather green blacks.

I would create a new profile from the measurement set, or better - measure the profiling target again and make a new profile from that. Maybe this was just a fluke in the profile generation. Did you save the measurement file, and have you brought the measurement into the ColorThink Grapher? You can compare the measurement with the profile that was made from it, and the outer boundaries of the two should align like they belong together. This is a good simple check for profiles.

At 5:47 PM -0700 6/7/11, keconomos wrote:

Sorry for the long delay in replying to this message. I’m not sure why we missed it… anyway,

thanks for the screen shot. A picture does say a thousand words.

well, at first blush, I see a very light max black. Can the printer really only get down to L*=25?

That has a pretty big effect on things as after 75%, there’s nothing else to be done.

With the light max-black, there’s quite a quick ramp for black to make from 30 up to around 95% and once it gets past 65% the gray balance seems to be shot…

I’m more worried about the low level of yellow the profile wants.

While the profile’s output to achieve gray balance does seem a bit whacked I think that the linearization and perhaps the total ink in each channel might be the root cause. Starting black earlier (if it won’t cause speckling) might help things as well.

Finally, if you can get it to print any darker, I’m sure it would help. If it looks quite dark to the eye then your instrument may not be up to the task of measuring shadows on that medium. A good ol’ SpectroScan with a polarizer might fix things up nicely.



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