OBA, M1, M2, and M3 — and the Things That Could Go Wrong (Part 2)

Editor’s Note: A few years ago, writer and color management expert Kevin O’Connor — (1954 – 2019) — delved into the complicated issues regarding optical brighteners in press sheets. Because optical brightening agents (OBAs) and the M standards are still confusing to many, we bring his article back to light, with updates on the technology and how it has fared over the past three years.

We remember and thank Kevin O’Connor for this in-depth article written shortly before his death in 2019. The original version was published in Rods and Cones’ magazine Out of Chaos. It has been edited to reflect current practices and thinking. 

For Part 1 of this two-part series, please click here.

M2: Removing UV entirely from the workflow (when possible)

M2 defines a measuring condition completely devoid of ultraviolet light from the measuring light source. It was developed to address issues in trying to measure and profile substrates with increasing amounts of OBAs. The spectrophotometers saw the fluorescence not as brighter whites, the way human eyes see fluorescence, but as increased blue-violet. Profiles made using these measurements would often introduce a shift in paper color to yellow, offsetting the measured extra blue-violet and giving a dingy appearance. Removing excess blue-violet from the measurements solved this problem but could introduce other color issues. For those not wanting to use OBA-infused papers, nor view output in light with a UV component, this may be an M standard to consider.

In this standard, the light used to measure color does not have any UV component to excite the optical brighteners. These instruments were originally referred to as “UV-cut.” A filter was used to cut out any UV from illuminating the sample being measured. Some contemporary instruments achieve UV removal by filtering; others have light sources that don’t produce enough ultraviolet to need filtering.

The absence of ultraviolet in the light source means that if any measured substrates or colorants have brighteners, the instrument will not measure their presence. However, if the viewing environment has enough ultraviolet in its light output, the measured substrates or colorants will fluoresce in the light, and color won’t match. This argues for caution in using M2 in any light where the sources are not strictly controlled to remove ultraviolet.

Who should consider using M2 and why?

1. Those creating output that will never be viewed under final lighting that includes ultraviolet could use M2. Examples of UV-free environments include the UV-blocked lighting in a museum, filtered to prevent UV from damaging art on display. Both non-OBA and OBA-brightened papers can be used for display in such a lighting environment.
2. A fine art print workflow may be a perfect place to use this standard. Fine art substrates should never have optical brighteners in them. Artists should be testing to be sure their substrates have no OBAs. The OBA Index uses M2 as part of its procedure to measure the amount of fluorescence present due to the presence of OBAs.
3. In this workflow, artists measure without ultraviolet to calculate profiles for their final output, then print and can view with or without ultraviolet because there is no brightener in their art to respond to any UV. However, the absence of brighteners in their papers means the papers will cost more to achieve a brighter white appearance compared to papers made with brightening agents. Artists use papers without brighteners because OBAs in paper fade over time, gradually changing the appearance of their work.
4. Standard printed materials that will also be displayed under UV-blocked lighting, such as that in museums or next to artwork, are another category where measurement could be done cutting out UV to correctly print and display, whether the substrate has OBAs or not.
5. People who only have legacy UV-cut instruments must measure using M2 until they acquire more flexible instruments.
6. Perhaps the most tempting use of M2 is for people who simply don’t want to deal with addressing the complexities of compensating for optical brighteners, but do want the precision that comes from measuring without having to worry about any ultraviolet being present. In theory, M2 is a great workflow to adopt when ultraviolet is removed from the viewing environment, and color measurements are made of substrates and inks that have no ultraviolet — in other words, no UV at any step of measuring, printing, and final viewing. This is similar to a pre-2009 workflow, ignoring or excluding ultraviolet considerations, but with increased precision. That neatly solves the problem of mismatches caused by optical brighteners, as there will never be any ultraviolet to cause a problem.

What are the disadvantages?

1. The number of final destinations for output where there is no ultraviolet light is limited. When the output created on OBA-infused substrates or using fluorescing inks are displayed in UV-included lighting, the presence of any unmanaged OBA component may cause a dramatic mismatch.
2. The challenges of using contemporary viewing environments to match a proof and final output made with M2 measurements can be difficult to surmount. For this reason, some professionals recommend M2 be used only when making final print output on OBA-free substrates, not when trying to match a proof from one device to a print made on another device.
3. Most importantly, UV-cut devices can cut out part of the visible spectrum when measuring, in addition to ultraviolet. The violet-blue shades in the lowest part of the visible spectrum that can be cut out in M2-enabled readings can skew profiling to deliver unacceptable results. Many professionals believe the M2 standard should almost never be used. If it is used, profiles should be carefully evaluated for unwanted results.

M3: A polarizing solution (press operators may find particularly useful)

Photographers who’ve captured images of glassware and other highly reflective objects will recognize the foundation of the M3 workflow — it starts with M2 and adds in double polarization.

When you polarize both the light source and the reflected light, with the two filters set at 90° angles to each other, you diminish specular reflection that blocks correct measurement. While polarization helps to minimize specular reflections, it requires a spherical spectrophotometer or a larger aperture used to read highly textured surfaces.

M3 defines a measuring condition where:

1. There is no ultraviolet used when measuring.
2. The light used to measure is emitted through a polarizing filter.
3. The polarized light strikes the object being measured, and bounces back to the measuring sensor through a second polarizing filter, removing specular reflection.
4. Measurements can be made of density, such as patches of wet ink, with the goal of removing the delay in waiting for the ink to dry before measuring.
5. Measurements can also be made of color for profiling if the instrument supports profiling.

Who should use M3 and why?

1. Press operators can check density without waiting for the time needed to measure ink drydown. While this technique is not much used in the United States, it is used in Europe, and is correctly supported using M3. Used in conjunction with good color management techniques, the M3 measurement condition can be used to add a tighter level of process control as the press is running.
2. M3 can be used to measure highly textured or three dimensional substrates and fabrics for color management. It can also be used to measure color in artwork, such as chunky, textured layers of paint. The polarization diminishes false readings caused by light reflecting at multiple angles. M3 may not be enough for these goals, so measuring the items described above may require an integrating spherical spectrophotometer, or a spectrophotometer with a larger aperture for best results.
3. Some field testers have reported good success using M3 to profile dye-based inkjet printers.

What are the disadvantages of using M3?

1. The M3 measurement condition, when used to measure density, may deliver readings that are slightly darker than the other measuring conditions, and may require fine-tuning to compensate.
2. Few instruments are currently available to directly support M3 profiling measurement. The Barbieri LFP is one currently shipping.
3. It can be difficult and time-consuming to get data sets from other M3-capable instruments to import into color profiling software to calculate profiles, as those instruments need software yet to be written to accept these measurements.

Conclusions
With the release of the M Standards, press output providers have been invited to enter a brave new world, one where proofing and final output can more easily be properly matched for many clients, using contemporary proofing substrates. Users who implement these standards for their workflows will have a higher probability of matching proof and output in much of the lighting conditions found in the real world, not just the sheltered sanctuary of the press house. However, other lighting will still prove challenging. Other workflows can also benefit from the improvements introduced in new measuring technology and lighting, though these tools can disrupt workflows that were working adequately in the past for many people.

Resistance to implementing the standards is not surprising. It requires mastering the concepts while investing in new equipment, and requires changing workflows and thought patterns, all while working in a deadline environment. The lack of easy, clear instructions is a barrier for many, though that problem is easing as an increasing number of consultants gain ground in mastering implementation of these standards, while both consultants and various professional groups offer sets of clear directions on how to master these workflows.

More precise standards for measurement capabilities in contemporary instruments empower users to collect more useful data if they choose to take advantage of the empowerment. Multiple challenges still exist, and standards, tools, and workflows will continue evolving to meet them. More precise workflows can save money and improve customer satisfaction while drawing in new customers.