In my travels helping companies achieve G7 Master Printer Certification I encounter lots of creative ways of managing color on press. Lots of folks have a densitometer at the press console to spot check sheets. While this has undoubtedly greatly improved the consistency of press color on each station over time it becomes obvious that some densitometers do not correlate to each other when measuring the same press sheet and ink zone. Which densitometer is correct?
One resolution is to send a densitometer back one at a time to get re-certified by the factory. This will ensure at the very least the factory has confirmed the device is operating and performing within acceptable measurable tolerances defined in the certification sheet included in the return shipment.
Is your densitometer measuring accurately?
Techkon takes this crucial concept one step further enabling their customers to verify multiple instruments to measurements alike in-between factory recommended re-certifications (24months). Connecting a Techkon SpectroDens by USB to PC running Techkon’s Connect software and Techkon Spectrocheck module allows multiple SpectroDens to be verified against a color reference. The Techkon Spectrocheck consists of four colored ceramic tiles that rotate on a lazy susan style cradle. The verification process is easy with the Techkon Connect software showing pictures of how the device should sit in the cradle. A label can be printed with the results of the verification.
The G7 near neutral calibration method is established in US commercial printing industry as a preferred method for press and CTP calibration. Many of our commercial printing clients have older densitometers prior to the G7 revolution. Though we are able to show them how to correlate correct target solid ink density measurements for their densitometers invariably they are enamoured by the bold simple display of the Techkon SpectroDens for G7 refinement. The Techkon SpectroDens displays corrective moves that a pressman can immediately implement on the press console. Older spectrodensitometers do not display “press moves” on the LCD screen, nor do densitometers offer this functionality.
What’s your shop’s colorimetric tolerance?
One of the lively discussions I like to have with a pressmen is what is an acceptable deviation allowed across the sheet? I have heard a lot of interesting explanations of how and why their tolerances are meaningful and absolute. Sometimes I hear differing explanations and tolerances from pressmen at the same plant!
Simply put measuring variance across a press sheet should be done using a meaningfully weighted color differencing models of CMC, dE2000, and dE94. These color models provide a good correlation between what we perceive and what the measurement device is reporting. Metrics of density do not correlate well to human perception but are excellent at recording meaningful variances.
A tool I find helpful for spot checking different ink zones against one another is the SpectroDens InkCheck. Instead of relying upon density, which does not correlate to how the eye responds, the SpectroDens InkCheck uses spectral (colorimetric) measurements to see what variance in Deltaa*b* is occurring across the press sheet. Using colorimetric delta-e is a simpler and safer method since the defined variance have real world implications to the viewer. The CMC, dE2000 and dE94 tolerances are weighted based upon continued research in how humans respond to color. Therefore it is easier to define a shop’s tolerances as deltaa*b* to ensure similar color quality across different presses and operators.
Densitometers can’t report this useful metric. Older spectrodensitometers can be upgraded to report some of the new G7 metrics but fall short in displaying an easy way for operators to use in production. Start extrapolating how much it costs to not move jobs around because the color match can’t be consistent, then think about the waste/spoilage that happens from everyone sharing numbers (SID) around the shop that result in further problems in achieving similar quality printing among presses.
An easy way to minimize a shop’s color variance among presses is to use instrumentation from the same manufacturer. The Techkon SpectroCheck ensures instrumentation is working with tolerances between factory recommended re-certifications.
— Dan Reid is a color management and G7 Certified Expert at RPimaging, INC.
RPimaging, INC helps clients achieve the benefits of G7 calibration in a matter of days. Learn more about RPimaging, INC services and products at http://www.rpimaging.com
by Dan Reid, RP Imaging