Posted by Elaine Becker on Wed, Jun 16, 2010
This blog post was authored by John W. Root of Mt. Baker Research.
Workers in digital imaging and publishing use color management to achieve consistency throughout a workflow. The goal is to preserve the quality and accuracy of an image from capture to final reproduction. Each device in the workflow supports a different color space. The available color management systems profile the gamut capabilities of each device, and then limit the working color space to the gamut that is shared by all of them.
The workflow used by color metrologists is different. Many labs employ more 
than one instrument to measure color or appearance and to assure quality control. Here we'll focus on measurements of spectral reflectance factors ("SRF") for uniformly colored samples. A spectrophotometer is used to measure SRF data throughout the visible spectrum, which extends from 400 - 700 nm.
Different instruments may not output the same SRF data based on measurements of the same transfer standard. In this situation tests of inter-instrument agreement may be used to measure the consistency between the participating instruments. Depending on the outcome of these tests, color management may be required to enable the meaningful sharing of SRF data.
Inter-instrument agreement cannot be achieved unless the test instruments employ the same geometry. See Color Geometry: A Matter of Degrees (another post within this blog) for a discussion of geometry.
In printing and the graphic arts metrologists who use sphere-based instruments employ the (d/8°) diffuse hemispherical specular-excluded ("SCE") geometry. Others prefer the (0°/45°) or (45°/0°) bi-directional geometry. Because gloss is important in the manufacture of paints and architectural ceramics, in those industries metrologists prefer the (t/8°) total hemispherical specular-included ("SCI") geometry, although certain segments of the coatings industry, namely coil coating, have standardized on 45°/0° geometry.
Among comparable instruments that use the same geometry, other factors may lead to differences in the measured SRF data. Before listing these factors, we stipulate that the instruments to be compared are maintained in good working order, and that suitable procedures are used to achieve consistent sample quality and to measure accurate SRF data.
Differences in the SRF values measured by comparable instruments may result from the following types of wavelength-dependent error: (1) Photometric scale. (2) Wavelength scale. (3) Bandwidth.
The standard multivariate regression procedure that is used to characterize these errors was described in the open literature more than 20 years ago. In a complementary approach, during 2009 the author developed transfer standards that are optimized for detecting these errors. For more information see Color Measurement Accuracy: Diagnostic Procedures (another post within this blog).
The multivariate regression procedure detects and measures the following errors: (1) Photometric zero (black point). (2) Photometric linear scale (100% reflectance line). (3) Photometric nonlinear scale. (4) Wavelength scale. (5) Bandwidth. This method cannot compensate for differences in instrument geometry, or for the errors that result from thermochromism or lateral diffusion. For a discussion of translucency see Color Measurement Accuracy: Translucent Materials (another post within this blog).
CyberChrome's OnColor Profiler® profiling system can analyze the errors listed above on most of the instruments that are in use today. This system includes software and 32 reduced-translucency transfer standards that are optimized for profiling. The OnColor Profiler® software compares the SRF data measured on each test instrument with data from a master instrument. The software generates correlation coefficients, or correction factors, that may be used to improve inter-instrument agreement with the master instrument. See How to improve Inter-instrument Agreement with Instrument Profiling (another post within this blog).
The author of this article is John W. Root Ph.D. of Mt. Baker Research who can be reached via email at jackroot@mtbakerresearch.com.
Posted by Elaine Becker on Thu, May 27, 2010
This blog post was authored by John W. Root of Mt. Baker Research.
During 2009 Mount Baker Research introduced transfer standards and procedures for 
diagnosing instrument errors. Parts A and B of the Diagnostic Tile Set each contain 16 2 x 2 inch ceramic color standards. Part A supports instrument testing and the assessment of inter-instrument agreement in a multi-instrument environment. Part B enables licensed users of part A and CyberChrome's OnColor Profiler® software to upgrade to profiling.
The part A standards were selected to meet the following criteria: (1) Span the complete photometric range. (2) Span the widest possible high-chroma gamut in CIELAB color space. (3) Include only high quality standards with minimal translucency.
List of Supported Tests
1. Instrument Validation. For this test the part A standards must be pre-calibrated in the geometries of interest. (Three geometries are supported.) After the user measures spectral reflectance factors ("SRF") with the test instrument, statistical data analysis is used to diagnose its performance and compare it to a reference instrument.
2. Absolute Accuracy. To characterize the absolute spectrophotometric accuracy, the SRF data from the validation test may be compared with data measured at NRC for similar transfer standards. At present this test is supported for the (0°/45°) and (45°/0°) geometries.
3. Inter-laboratory Agreement. The agreement test is performed when the white calibration tile supplied with the test instrument is traceable to a standards laboratory other than NRC or NIST. This extension of the validation test measures differences in the photometric scales between the laboratories on which traceability is based. Based on the results of recent beta tests, this systematic error may significantly exceed the statistical uncertainty of the SRF measurements.
4. Instrument Revalidation. Repeating the validation test provides a basis for tracking instrument performance and for checking the user's methods for storage and maintenance of the transfer standards.
5. White Calibration Tile. If the white calibration tile supplied with the test instrument is translucent, significant measurement errors may result. Provided that LAV and VSAV sample ports are available, the part A set may be used to diagnose this problem.
6. Translucency Sensitivity. The part A set may be used to measure the sensitivity of the test instrument to SRF errors that result from lateral diffusion. This test requires the use of LAV and VSAV sample ports. For more details on translucency, refer to the blog "Color Measurement Accuracy: Translucent Materials"
7. OnColor Profiler®. Profiling improves inter-instrument agreement in a multi-instrument environment. This may be accomplished using the combined parts A and B standards together with CyberChrome's OnColor Profiler software. Part B of the tile set adds 16 more chromatic colors to better map the color gamut. For more information on the benefits profiling offers, read the white paper on this topic.
The author of this article is John W. Root Ph.D. of Mt. Baker Research who can be reached via email at jackroot@mtbakerresearch.com.
Posted by Elaine Becker on Wed, Apr 28, 2010
CyberChrome Inc was an exhibitor at the recent American Coatings
Show in Charlotte, NC. Featured products included OnColor Profiler for improving inter-instrument agreement and the OnColor Suite of color management software for quality control and color formulation.
According to the press release from the American Coatings Society, "With 328 exhibitors and about 6,700 overall participants (2008: 331 / 5,600), the second edition of the American Coatings Show & Conference was hugely successful as the highlight event of the US paint and coatings industry. The combination of trade show and conference, held April 12-15, 2010 at the Charlotte Convention Center, North Carolina, thus once again exceeded all expectations."
Attendees came from not only North and South America, but there was a strong presence from Asia as well. Visitors at the CyberChrome booth included many US companies but also companies from Canada, Mexico, India, China, and other Pac Rim countries.
Interest in instrument profiling was high as companies struggle to manufacture to the same electronic color standards with tight color tolerances around the world. OnColor Profiler helps to meet the objective by providing much tighter inter-instrument agreement and allows them to meet the rigid color tolerances demanded in today's market.
Many larger companies are also interested in placing color matching systems at their distributor locations where they can match their own custom colors and reduce the burden on the color lab at the main facility. It also allows distributors to turn around custom matches in a much shorter time. CyberChrome's Match Express software provides an affordable and easy to use software package for distribution locations.
While attendance was "decent" at this show, exhibitors and attendees both wonder about the future of trade shows such as this one. With internet meetings, webinars, and the high costs of travel, it seems like fewer and fewer people attend these shows. There is still much to be said for face to face meeting, ralationship building and the social interaction that happens at events like this. What are your thoughts on attending trade shows in the future?
Posted by Elaine Becker on Thu, Apr 08, 2010
This blog article was written by Dr. John W. Root of Mt. Baker Research:
A translucent solid is not perfectly opaque. Part of the light incident on it penetrates the surface where it undergoes internal scattering and lateral diffusion away from the entry point. Both processes reduce the intensity of reflected light.
Because of lateral diffusion, the reflectivity of a translucent solid decreases as the size of the instrument's sample port is reduced. This effect causes systematic errors in measured spectral reflectance factor ("SRF") data. The magnitude of these errors depends on the following: (1) Instrument geometry. (2) Characteristics of sample surface. (3) Sizes of illuminated and measured areas of sample.
Measurement of Translucency
In commercial spectrophotometers that support diffuse illumination, the entire exposed surface of the sample is illuminated and an optical system controls the area viewed by the detector. Over-illumination is achieved by configuring the viewed area to be smaller than the illuminated area. Experiments in which over-illumination is varied can be used to measure the fractional reflectance losses ("FRL") that result from lateral diffusion. The author recently used this technique to measure FRL values for many ceramic tiles, glasses, and plastics.
The X-Rite ColorEye 7000A ("CE7000A") spectrophotometer supports a wide range of over-illumination. Maximum over-illumination is achieved with the LAV/VSAV configuration in which the LAV sample port is combined with the VSAV lens setting. The VSAV/VSAV configuration minimizes over-illumination.
The typical FRL results reported below were calculated from SRF data measured using the LAV/VSAV and VSAV/VSAV configurations of a recently purchased CE7000A (S/N 37132651108). The success of this method requires that the instrument's white calibration tile exhibit negligible translucency. This was the case for the author's new CE7000A, but not for his 2nd instrument (S/N 37116190602).
Translucency in Transfer Standards
The author's tests demonstrated that many optical materials exhibit translucency. For the FRL values listed below the 2σ standard error of estimate is ± 0.03%.
Typical Values: White Carrera® glass, 25.6%. Extruded Teflon®, 22.9%. White Vitrolite® glass, 18.9%. Ceram red-orange 99/1 tile, 8.98%. Sintered PTFE powder (Fluorilon® and Spectralon®), 3.6% - 2.9%. Ceram red tile, 3.14%. MC-20 Russian white opal glass, 3.13%. Ceram orange tile, 3.03%. Ceram yellow tile, 2.52%. X-Rite white calibration tile (S/N 37116190602), 1.43%. Konica-Minolta CMA103 white tile (S/N 18776042), 0.90%. X-Rite white calibration tile (S/N 37132651108), 0.00%.
Although FRL values may be measured using other instruments, the results will depend on the translucency of the instrument's white calibration tile as well as the dimensions of its LAV and VSAV sample ports.
Comparisons of SRF data measured using instruments with large vs. very small sample ports should be based on opaque transfer standards. If the standards are translucent, inter-instrument agreement cannot be achieved. Instrument profiling cannot mitigate the errors that result from the following sample characteristics: (1) Thermochromism. (2) Translucency. (3) Surface inhomogeneity.
The guidelines listed below are based on the sample port sizes of the CE7000A. They are recommended for transfer standards that are used for testing and profiling instruments in the diffuse SCI geometry. The FRL values should be less than 3.5% for instruments that support over-illumination and a LAV, MAV or SAV sample port. For instruments that support a VSAV sample port, the values should not exceed 1.5%.
The author of this article is John W. Root Ph.D. of Mt. Baker Research who can be reached via email at jackroot@mtbakerresearch.com.
Posted by Elaine Becker on Thu, Jul 16, 2009
So many color disputes arise these days because color instruments don't necessarily read the same. Electronic color standards are widely used and shared within a supply chain and have many benefits, but if all of your instruments are not regularly monitored and are known to read the same, then problems can arise.
Many users assume that since they do a daily calibration on their instrument, their readings are correct. And if they are correct, then they must match every else's. That's not usually the case. Spectrophotometers from different suppliers may read color differently. Even with the same model from the same supplier, significant differences can be found depending on the age of the instrument and how well it is maintained.
In order for electronic standards to "work" within your supply chain, you need to be able to recall a stored standard, measure the actual stored standard on another instrument and have a resulting DE of 0.15 or less. The number of 0.15 is dependent on how tight your tolerances are. If you are trying to supply a color match that is < 0.5 DE, then you certainly don't want to have half of that deviation taken up by lack of inter-instrument agreement. A good rule of thumb is that no more than 25% of your tolerance should be given up to instrument variables (such as INTER-INSTRUMENT AGREEMENT, sample repeatability, and instrument repeatability). So if your tolerance is DE=1.0, then you can live with measurement uncertainty of up to 0.25 DE. If your tolerance is DE < 0.5, then you can live with an uncertainty of no more than 0.125. So as tolerances get tighter and supplies get more critical of color, INTER-INSTRUMENT AGREEMENT becomes more important. Instrument profiling can help you achieve the INTER-INSTRUMENT AGREEMENT that you need in order to meet these tight tolerances.
One advancement in color technology in use today is instrument profiling. Instrument profiling is used to make a population of spectrophotometers read to within a tighter specification of each other. A master instrument is used as the reference point and all other instruments are "cloned" to match this master instrument. A complex set of equations is used to profile or "correct" a target instrument so that its spectral data mimics that of the master. After profiling, all data taken on the target instrument is now corrected to match the master. The result is much tighter agreement between instruments which leads to fewer disputes over whether the color match is acceptable and faster acceptance and approval of submits.