June 11, 2021

Understanding Instruments and measurements

What is an absolute color value?

Answering this question brings us to the conclusion that there is no simple answer. ChromaChecker offers a unique technology that helps to build a bigger picture of what factors have an influence on final color measurement results. 


CC Instrument Inspector T42 target

Our methodology is easy to understand. We have created T42 Target - printed with extremely high tolerances. The T42 target contains 42 selected color samples that cover optimally the whole spectral range that is typically used in industry. 

In the next step, we are measuring the same target with different instruments using all settings that are user-changeable. Depending on the instrument we can switch:

  • M-condition: M0.M1. M2 or M3
  • Measurement mode: scan, spot, contactless 
  • Aperture size (some instruments can adjust id dynamically, same have to be specified when ordered from the vendor)
  • Other vendor-specific compatibility modes (e.g.  M1-Part2 Export for eXact) 


We know that instruments will report different results caused by differences in:

  • Geometry 
  • Spectral resolution
  • Spectral range
  • What is measured

It is hard to understand that measured object has direct input on results - but research made by different vendors and researchers is also very good documented by ChromaChecker. If we compare two different instruments on a given set of patches ( H-100 in the case of ChromChecker) we see that harmonization data are very different depending on substrate/inks combination.  In the case of coated paper that we select for the tests and proofing paper that is intended to stimulate this production paper the difference in e-Factor is more than twice bigger for proofing paper... To learn more go deeper into Harmonization by CC.


Measurement accuracy can be affected also by:

  • Patch size
  • Backing
  • Scanning speed
  • RHT parameters

We created Target with a 21 by 22 mm patch size. To improve accuracy we are measuring each patch in 4 different locations - data are averaged. Our target has self-backing to avoid issues caused by improper backing. Patch size and our video tutorials make the scanning process better standardized. 

Going back to our methodology we are creating series of measurements to be averaged and saved as a baseline. For one Instrument we can create as many baselines as required - corresponding real scenarios of usage in the production chain. Baselines represent how our instrument "sees" all 42 samples of T42.

At this stage when we have baselines we can compare them and see if differences come from consistent, predictable reasons that we can describe with formula. It is a first step to qualifying for instrument harmonization. T-42 is not designed for Instrument Harmonization - which requires specific substrate/ ink combination - but due to patch characteristic is perfect for qualification before dedicated H-100 target will be applied.


Why the difference?

  • Technical solutions used by instrument vendors are different. Today there is a tendency to collect all M-condition data in a single pass. In some cases instead of changing the UV component in the light, a match formula is calculating the result.
  • To measure reflected light an object has to be illuminated. The source of the light build-in into the Instrument should be standard illuminant A for M0 and D50 illuminant for M1. In the case of M2, it should be a UV filter and additionally for M3 UV + polarizing filters together... In the real world, we have a kind of D50 simulator that is spectrally very far from the theoretical definition. So the engineers are applying correction formulas that are never perfect...
  • For industry, we need as small patches as possible and the fastest speed available - but that ruins accuracy. 
  • When we observe ink on paper with the microscope we will understand that it is not a flat surface covered with ink - a non-consistent 3-dimensional structure where we don't have 0/45 or 45/0 geometry ...
  • We are often measuring wet, inks, an black backing, sometimes vernished... - only if we think about varnish it is a transparent material that changes a lot of light distribution in our 3-d structure... 


No standard for the color that vendors can apply.

It sounds like a big problem - and it is. We have a definition of most units like 1m, 1°K. 1 sec. , but do we have a specimen - internationally approved of any color with the spectral definition of how this color template should be reported by 0/45 instrument when M1 condition is applied?

Are BRCA tiles an answer? - Definitely NOT. There is no way to produce tiles that are identical and there are spherical measurements made by the manufacturer with their instrument but there is no way to translate those data to 0/45 M1 D50/2°... So what is a real practice in the industry? If the vendor wants to sell a new instrument is trying to match another that is on the market...? Which one? How to do that? To be able to sell new products the vendor is "adopting" reading to match competitors. In many cases, they had better data before - but they have to be comparable to what is already - forgetting the reasons why we have already bad data.  Nobody can easily compare and understand what is going on.   As soon as an industry will create a standard we are going to have different results - and due to no objective standards no way to fix the global issues. And this is a state that unofficially engineers from all key vendors are saying the same - but don't expect an official statement.


What we can do?

  • The first is understanding what kind of instruments are already implemented in your production chain. Each Instrument has to have specified baselines to create a unique fingerprint of each in the system.
  • The second step is to document differences and analyze the current situation.
  • Evaluate if differences can be harmonized (Print Inspector) or correlated (Display Inspector). Take into account that harmonization or correlation is the process that is demanding - required effort from the management point.
  • Select measurements modes and instrument settings that are optimal for the process.
  • We can educate operators on how to measure to reduce inaccuracy, create an SOP for them to work with standardized conditions (frequent instrument verification, flat tabletop covered with a proper backer,  RHT requirements, checking calibration plaque, etc. )  




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