On Nov 4, 2013, at 12:15 PM, Marc Sitkin <mbs@digitalmomentum.com> wrote:

I'm using a rather old color checker and RPP64 for profiling, and am getting peak errors of deltaE 11, and average errors of over 4. Is it possible this is related to the age of the target, and if so, how long should one be kept before replacing?

A lot will depend on your workflow. It would be trivial to get those kinds of errors with bad technique. If you have (access to) a spectrophotometer, you can do two things. First, you can compare your ColorChecker against any of a number of online measurements; Bruce Lindbloom's is reliable and he's got calculators and spreadsheets out the yin-yang to put the data into any format you can dream of. Second, regardless of the condition of your ColorChecker, you can (and should) use those spectrophotometer measurements for profiling instead of whatever generic values you're currently using. It's proven to be a remarkably reliable tool over the years, but there _is_ variation from batch to batch (even if minimal). I'll close by noting that 24 patches is nowhere near enough for critical work. The Passport is far superior to the classic in all respects, and the ultimate field tool for normalizing white balance and exposure. But for critical studio work, especially reprographic work, even it's not really up to the task. For that, you should either plan on spending many hundreds on a not-bad chart or many hours in making your own really, really good chart. No particular skill is required; just a fair amount of mindless work. Cheers, b&

I'm using a rather old color checker and RPP64 for profiling, and am getting peak errors of deltaE 11, and average errors of over 4. Is it possible this is related to the age of the target, and if so, how long should one be kept before replacing?

The limitation here is the matrix type profile. It is important to realize that the profile error is calculated from the same target, and is simple deltaE, and as such it mostly shows the method limitations, not the profile accuracy. In deltaE2000 metrics max error will be less, probably about 5-6. It is definitely useful to measure the ColorChecker, you may get more accurate results but the error most probably will be the same, may decrease by 2 deltaE (regular deltaE, not 2000). Max error of 11-12 is typical for matrix-based profiles from ColorChecker. To get better results one needs ColorCheckerSG and may try LUT-based profiles ignoring noise added by LUTs - if not much digging into shadows is performed the noise LUTs add is quite tolerable. That does not mean it is easy to shoot any target, including regular ColorChecker with the quality needed for accurate profiling. It is also very important to understand that spectrophotometers are not 100% accurate and may have errors reaching and exceeding 3deltaE, even if freshly re-calibrated at the factory. Also, you can easily have 3 to 6 deltaE variation across the sensor. Profiles need to be checked not only by deltaE, but by visual inspection of the results of their application.

Thanks

-- Marc Sitkin

digitalmomentum, llc. 1700 NW 15th Ave Suite 360 Pompano Beach, FL 33069 954-973-2670 phone 888-880-5851

web site: www.digitalmomentum.com marcsitkinphotography.com wideandnarrow.tumblr.com _______________________________________________ Do not post admin requests to the list. They will be ignored. Colorsync-users mailing list (Colorsync-users@lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/colorsync-users/iliah.i.borg%40gmail...

This email sent to iliah.i.borg@gmail.com

-- Best regards, Iliah Borg