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March 21, 2022

Select right Instrument / methodology / software

Instruments based on 0/45 or 45/0 geometry are widely used In the graphic industry. This geometry is perfect for printed samples when the surface is flat and even. If the surface is not flat or even, measurements may be inconsistent to one another. If unsure about the surface characteristics, a number of measurements should be taken from the same position, and rotate the instrument around the same position and compare the measurements. Understanding different important instrument variables are critical to defining an efficient methodology for color manufacturing.

 

Before continuing with this article, make sure you understand the following basics, 

 

 

 

Goal: notes

Evaluation 

  • Visual match to physical sample
  • Measurement match to given colorimetric number (Lab)
 Evaluating the measured result against a physical sample is challenging. It is critical that the instrument measures with the same illuminant and same M condition as the sample will be judged. If these do not match, then you will have a lot of trial and error to get the color to match the physical sample. Light-Booths, light tables, Press-consoles being used to evaluate color need to match the instrument settings in order to get a physical match from a measured sample to the original reference. Some times it is only necessary to ensure the manufacturing process matches a given digital reference over time to ensure consistency and repeatability. In this scenario, it is not as critical to align the instrument with the viewing conditions.

 What is a Standard?

  • Physical sample
  • Digital: colorimetric (Lab, xyz) values
  • Digital: spectral value (30-32nm)
  • Multiply spectral values
  • Physical standards are subject to aging. Consistency is important, not all physical samples are uniform.
  • Colorimetric coordinates are only defined with a single Observer/Illuminant, if the actual lighting does not match the colorimetric values, then metamerism which results in a color mismatch will probably be an issue. In addition, if the sample has fluorescence, this could also lead to mismatches.
  • Some variables can be managed using more than one spectral curve. SPIN + SPEX enables calculating spectral glossiness; M1and M2 measurements are required for Fluorescence tracking; some semitransparent objects might require two measurement geometries tracked at the same time. 

Is Color Specification well known?

  • Is it common D50/2° or any different?
  • Is M-condition, Aperture, geometry, SPIN/SPEX defined?
  • Is definition based on a specific instrument type/model?
  
 Is tolerance simple or stacked (multi-level)?  Is there one instrument involved in the assessment of the color reproduction, or are there multiple instruments at different locations involved with the assessment of the color? Just one instrument provides a simple tolerancing workflow. Having multiple instruments, especially different makes and models of instruments will make the tolerancing very complicated, and "stacked" in that the inter instrument disagreement is additive (stacked) between all the instruments, increasing the error significantly in the process.
 Is the object printed on paper, or colorized in different process? Printing is a very specific technology. In most cases, we are using CMYK on nCLR process to create a complex pattern of semitransparent inks that cover paper or textile substrate.
Ink pigmentation for process printing (CMYK) is designed to render as large of gamut (range of color) as possible. But not all production is process based, many production requirements are based on spot color (Brand Color) rendering. 
Is surface matte, uniform, homogenous, or rather is complex, textured, multilayer (e.g. laminated)?  
 Instrument Gauge Factor (Percentage) It is important to understand that there is no Standard Instrument - an objective way to measure color. One instrument can return various results based on settings. Two instruments of the same kind can measure similar but not identical. Different types of instruments will provide different results, and that is typical 
   

 

 

 

Define the Goal, then adopt Methodology

There are a few main goals. Each has several aspects that may have an influence on the defined methodology.

Matching Color definition  Process consistency to itself

Match a given colorimetric (Lab) value within X ∆E (00)- need to know the M condition, observer angle and illuminant, and ideally which instrument created the sample.

 Align your measurement device to have the same setting as specified for the reference (ie. M1, D50/2 degrees), and set the ∆E (00) requirements

Match a physical reference and reproduce on a given print process (RGB, CMYK)

 Align your measurement device to have the same illuminant as the illuminant to be used when making a visual match (usually D50 in printing), then build an ICC Profile for the given print process (this can be done with ChromaChecker). Then use virtual spot print and SpotVar to create the optimal color on given device to match the physical standard. 
   
   
   
   
   

 

 

 

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