Color QC and Matching Blog

Color Management: The Pathway to Consistency

 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.

Color Measurement Accuracy: Diagnostic Procedures

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.

CyberChrome Exhibits at the American Coatings Show 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?

Color Measurement Accuracy: Translucent Materials

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.

 

Spot On: Lessons from a Color-Matching Master

As the North American Manager of Color Services for Pittsburgh-based PPG, a $16 billion per year manufacturer of paints, coatings, chemicals, optical and glass, Shelley Sturdevant knows something about color matching. She manages and oversees color control for the Coil and Extrusion coatings business at 10 facilities nationwide, with a color palette currently holding over 100,000 colors.

We had the opportunity to spend a few minutes with Shelley as she shared some of what she's learned managing color for PPG over the years:

CyberChrome (CC): What prompted your move into digital color matching and when?

Shelley Sturdevant (SS): About 10 years ago we decided we needed to find the right tools, the right hardware and software, to manage our color needs then and into the future. We needed to build a foundation to manage our huge color palette, including some colors we've been managing for more than 30 years.  That's when we settled on OnColor.

CC: What were you looking for in a color matching software application?

SS: Two things primarily, speed and productivity. The OnColor software can search through 50,000 to 60,000 colors in seconds. And, uniquely, it gives you the ability to do very specific color calibrations. It's an important tool for us in the lab but it's also key to our production in batch correction so technicians at all 10 of our facilities can consistently produce the same colors.

CC:  Anything else?

SS: Compatibility with a range of spectrophotometers. That enables us to get the best hardware to pair with the software. These tools form the foundation of our house so to speak, but where it really gets interesting and valuable is what you might call the ‘attached garage,' that is, how we use it to interface with our customers.

Now, we're all speaking the same language, not just internally, but we can communicate that directly to our customers. About 40 percent to 50 percent of our customer base has adopted our software and hardware systems models and we train them how best to use it. We can all access the same database which we put up on the Web and they can see new colors, research standard colors, and get precise, reproducible results.

CC: What are some of your newest challenges?

SS: Working to comply with the new ‘green' regulations that have recently been enacted, specifically achieving maximum solar reflectance values (SRVs) without sacrificing the quality of the color match. 

These new formulations take the known color matching rules and throw them out the door.  The use of brown (blended) pigments to effect L value (versus traditional black pigments) creates new color matching models and obstacles.  So, we have to rethink how we match colors.

CC: Thank you for spending time with us.

SS: Thank you.

(Note:  Shelley Sturdevant can be reached on email at ssturdevant@ppg.com)

10 Surefire Ways to Improve Your Color Matching Results

Paying attention to details can help you get the most out of your investment in a color matching system, get you the best color match accuracy, and get your colors approved in the fewest hits.

1. It's all about the database.  Or what's under the hood? Color matching starts and ends with your color matching database. How good is it? How old is it? Just a few years out-of-date is a lifetime in technology improvements; five or more years borders on Paleolithic.
2. Sampling sense. Were your samples prepared in a manner consistent with how you actually manufacture your product? Are the raw materials  (colorants, bases, resins, substrates) you use today the same as you used when the database was prepared?
3. Reliable replication. Good science and good business practice require that results be replicable, easily and consistently. Will a sample made by your lab technician today match your original used in the database?  When preparing a new database, use your most skilled technician.  Temporary employees are barely a good idea at your reception desk, let alone a temp managing your colorant database.  Tighten up procedures and your color matching accuracy will tighten up too.
4. Trust everyone but cut the cards. Check your incoming raw materials, especially the colorants, for shade and strength. Don't assume they are always 100 percent strength and exactly the correct shade.
5. Standardize. Use standardized lots of colorants when you make samples. Get a COA from your supplier and note which lots were used to prepare the database.
6. Duh! Not quite as fundamental as, "Is it plugged in?" but be sure your database is properly loaded. You'll never get the right results with a database incorrectly loaded.  Look for negative data and wayward levels on the colorant build curve.  
7.  Optimize, then verify. Optimize the database and validate it using known samples. Repeat the process of validating the database using known mixtures at least once a year.
8. Know what you know... and what you don't know. Be sure you truly understand how to run your software. More important, be sure you know how to interpret the results and pick the best match for the task at hand. 
9. Think first, select second. Consider how the colorant combination will work in production before automatically selecting the "Best Match." Getting a practical, workable formulation up front makes production adjustments easier and causes fewer difficulties later. 
10. Apples to apples. Make sure your database was measured on the same instrument you are using. Differences between instruments will directly result in less accuracy in your matches and corrections. Using a "canned" database can seem like a good idea because it saves time and lab resources and pushes the responsibility onto someone else. However, if your measurements, procedures, and raw materials don't exactly duplicate those used to prepare the database, you may be very disappointed in your matches.

Are you happy with the way your colorant database is matching?

Color Geometry: A Matter of Degrees

Long before computers were invented a radio, film, and television comedy team known as Abbott and Costello perfected a classic skit that became known as the "Who's on First?" routine; essentially a dizzying five-minute display detailing by example the pitfalls of miscommunication via homophones, homonyms, home-run hitters, and high comedic art.

Not so funny is the frustration and confusion many working in color measurement experience due to the persistent misuse of terminology. "Why don't my color numbers match?" is a question we hear often.

The Many Angles of Color Measurement

Probably the most common misconception is about the 2° and the 10° observer.  This frequently gets mixed up with the geometry of the measuring instrument with users saying they measured the color at 10° using D65 illumination, when in fact what they measured the sample with was a 45° /0°  instrument using tungsten illumination. The 10° comes into play with the Standard Observer they chose for the tristimulus weighting functions.

There are two areas where these angles come into play and it's easy to see how they can become confused:

The first is the instrument geometry and how the light source and detector are positioned relative to the sample.

• The second is less obvious and goes back to how the tristimulus weighting functions are specified.

The 45°/0° refers to the geometry or optical design of the measuring instrument, be it a colorimeter or a spectrophotometer.

The most common instrument geometries used today are either 45°/0° or d/8°.

The instrument geometry is described by a pair of angles or letters. The first letter or number in the pair is for the angle of illumination; the second is for the viewing angle (or the angle that the light is detected).

 

So, for 45°/0°, the sample is illuminated at 45° off the normal (perpendicular to the sample) and the reflected light is viewed or detected at 0° (meaning perpendicular to the sample). 

In the second example of d/8°, the ‘d' stands for diffuse illumination, meaning the sample is illuminated at all angles by diffuse light coming from the integrating sphere. (The integrating sphere is the white-coated ball collecting and diffusing the light).

The second term in d/8° stands for the angle of viewing which is 8° off the normal.

 

 

 

Angling for better color management

So, what are the 10° and the 2° all about?

This seems to be where all the confusion is centered. These angles refer to the Standard Observer and have nothing to do with the geometry of the instrument or the angle at which the samples are viewed.

Instead, the 10° and the 2° angles refer to the field of view when physically viewing a sample. The field of view subtends either a 2° or a 10° angle on the retina.

A better way to understand this is that a 2° field of view is equivalent to viewing a 1.7cm circle at a distance of 50cm; a 10° field of view is equivalent to viewing an 8.8cm circle at a distance of 50cm.

So roughly, the 2° field of view is equivalent to viewing a 1.7cm circle at a distance of 50cm; or like looking at your thumbnail at arms length away and the 10° field of view is like looking at the palm of your hand (or a three-inch circle) at arms' length.

The color of consistency

In industrial color control, the 10° Standard Observer is recommended because it more closely approximates the size of samples being evaluated, but you'll still find lots of standards and procedures using the 2° Observer.

These terms are important when trying to communicate color up and down the supply chain. Being able to communicate precisely how the numbers were determined is key to someone else being able to reproduce them accurately.

And now, if someday you're out at the ballpark and someone asks you, "Who's on first?" you'll know to just tell them, "Yes," and let it go at that.

Color Me Stressed Out

If we put you under the spectrophotometer now, would you show up in deep shades of recession blue? Perhaps.

Tough economic times often mean having to make do with fewer resources to handle the workload. The same workload for developing new colors, adjusting production batches, and approving colors is spread over fewer people. Staff become stressed and can easily overlook color shifts they might otherwise have caught.

And, as you know, color shifts take time to correct. They result in product that either has to be reprocessed or worse, discarded, let alone the time and labor required to make the corrections.

Sometimes, it's the more experienced staff-the more expensive staff-that had to be let go, and along with them, went years of knowledge of how to work the color matching system or operate older, more finicky equipment.

But, just like a painter who switches from brush to roller and roller to spray gun, an investment in the right industrial color matching or color quality control technology can help ease the burden while increasing productivity and reducing costs.

Don't paint yourself into a corner

Investing in technology is one way to keep up with demand while keeping payrolls lean. 

Consider these advantages from a new, up-to-date, industrial color matching system:

Fewer production adjustments: The software can automatically calculate and add colorant to bring production back on track.

• Optimized adds: Color matching software can find the one, optimal colorant to add to correct a batch.
• Batch size variation adjustments: Color quality control software automatically calculates accurate adjustments by weight or volume, or even when the batch amounts are not known.
• Faster estimating: Detailed production costing lets you provide estimates faster, beating the competition to the bid.
• Wider color range: Today's sophisticated industrial color matching software databases help you reduce the number of colorants in inventory while broadening the range of colors you can produce.

This recession will end someday (or so they keep telling us). In the meantime, consider how technology can increase productivity, lower inventory, and keep staffing costs in check. Then, focus on the future, one with a bright, sunny, yellow outlook.

Report on the 11th AIC Colour Congress 2009 Sydney

The 11^th Congress of the AIC (International Colour Association) was held at the John Niland Scientia Centre, University of New South Wales in Sydney at the beginning of the month and was a highly successful event.

There were over 330 delegates of whom ~220 were from overseas in fact from 34 countries from most continents around the world.

The Congress showcased the latest research and development in all disciplines of colour study from architecture to design, measurement, psychology, philosophy, science and vision with the participation of leading international researchers. Over 130 oral papers and 80 poster papers were presented during the Congress.

The Opening Ceremony had a very strong Aboriginal component with a traditional Welcome to Country; which was very moving. Delegates also had the opportunity of being involved in a sand painting created by local artist Walangari Karntawarra.

 

 

A dynamic and colourful keynote address titled ‘Why are animals colourful? Sex and violence, seeing and signals was then presented by Professor Justin Marshall from the Sensory Neural Group, School of Biomedical Sciences and Queensland Brain Institute, The University of Queensland.

New features during and prior to the Congress were:

1. Pre-conference workshops

Master Class for Artists and Designers - Associate Professor Lois Swirnoff

Colour: Meaning and Communication - Associate Professor Dianne Smith

Introduction to Colour Psychology and Statistics - Professor Byron Mikellides

2. Overview sessions on the latest in research in:

          Colour Vision - Professor Paul Martin

          Colour Science - Professor Roy Berns

          Environmental Colour - Associate Professor Karin Fridell Anter

3. Two multi-disciplinary Symposia

          i. Appearance in Nature and Design

          Speakers:      Dr. Kevin Hellestrand - Underwater photographer and Cardiologist

Chalisa Morrison - Senior Design Colour and trim Toyota Design Australia

Gabi-Kigle-Boeckler Global Business Manager with BYK Gardner GmbH

            ii. ‘Good' and ‘Bad' Colours: Painting, Conservation and reproduction

          Speakers:      Dr John Gage - Fellow of the British Academy

Dr. Maria Kubik - Paintings Conservator Art Gallery of Western Australia

Professor Roy Berns - Richard S. Hunter Professor in Color Science, Appearance and Technology, Rochester Institute of Technology, USA

The seminars successfully met their objective of encouraging inter-disciplinary discussion and interaction.

There were over 20 papers relating to colour measurement and one session devoted to colour control in the automotive industry in addition to the Symposium on appearance.

The social functions included dinner on a Sydney Harbour Cruise and an excursion combining the Sydney Botanical Gardens and the Aboriginal Art Exhibition at the Art Gallery of New South Wales.

Copies of the Proceedings on CD are available for purchase at a cost of A$175.00 plus postage.  To purchase, please email: sales@nhpl.com.au .   Please note stocks are limited.

The 12^th Congress in 2013 will be held in Gateshead, England with interim and mid-term meetings:

2010: Argentina - Colour and Food - From the Farm to the Table

2011: Switzerland: - Interaction of Colour and Light

2012: To be confirmed

CyberChrome was a Congress sponsor.  Comments from any attendees are welcomed.  This blog post was written by the Conference Chairman, Nick Harkness of NHPL.  http://www.nhplcolour.com/ and nick@nhpl.com.au

 

Installing OnColor Color Software under Windows 7 and Vista

The OnColor  Suite of color QC and color matching software is licensed through use of a hardlock key.  The USB hardlock key that is shipped with the software can be used on one computer at a time. 

There are two ways to successfully install the Hardlock driver required for the USB key used by OnColor in Windows 7 and Vista:

1. OnColor setup will run HLDRV32.EXE (Included on the installation CD) which installs the Hardlock drivers.
2. Allowing Windows to install the Hardlock driver the first time the USB key is used.

If both driver setups take place, however, the Hardlock key will not work as the drivers conflict.

The preferred method is to follow our instructions and not insert the Hardlock USB key until after the setup of OnColor.  The OnColor setup will run HLDRV32.EXE, which will prevent the Windows drivers from being installed when the USB key is inserted.

If for whatever reason, the Windows driver for Hardlock has been installed before the OnColor setup, you must uninstall the HLDRV32 Hardlock drivers after the OnColor setup.  To uninstall the Hardlock drivers, go to the Control Panel -- Programs and Features, which shows a list of programs that can be uninstalled.  You should see "Hardlock Device Drivers" in that list.  Uninstall that program.  Unplug the Hardlock key and then reboot the computer.  Plug in the Hardlock key and you will now be using the Windows supplied Hardlock driver.

If you know that the Vista Hardlock key driver has already been installed by Windows, you can hit the Cancel button during installation of the OnColor CD when the Hardlock setup dialog is displayed and then continue on with the OnColor installation.