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Sunday, April 6, 2014

Practical Aspects of Color Matching: Color Measurement Systems

There is no "perfect" system for measuring and quantifying color, however, there are some very good ones.  A combination of a color management system and visual assessment is recommended to best match color samples.  The Technidyne Seminar Manual provides a good introduction to the different color measurement systems.

Spectral curves present the most complete method for comparing samples. The spectral curve is really the 'fingerprint' of the color under a given lighting condition. However, for many people, it is confusing to understand and control.
These spectral curves help illustrate differences between virgin and recycled newsprint.

The magnitude and direction of color differences between a sample and a standard can be easily determined and understood with a color measurement system.

L,a,b and L*a*b* 
These systems are widely used and understood in the Paper Industry.  These systems are good for pinpointing where a sample resides in color space in relationship to a standard; in a sense, a road map for getting closer to the standard (or target).  The delta values for L,a,b and L*a*b* help clearly identify the color difference areas. This allows the user to determine what controls to use to get a better match.

The CIE L*C*h system is an adaptation of the L*a*b* color space. L* represents lightness, C* is chroma, and h is hue (angle).  An extensive system for color matching has been developed using this system which provides excellent pass/fail tolerances that match with visual assessments very well.  This is called the CMC Color Difference Formula (see related blog). Using the CMC Formula the user selects a Commercial Factor that determines how far a sample can stray from the standard in color space and still be acceptable.  In the long term, this is an excellent system, but it would require extensive training of mill personnel.

If you want help determining the best color system for your situation or if you want training on how to use a color system, feel free to contact me.

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