The Color Bar

Color bars (a.k.a. color control bars, color control strips, or proofing bars) are essentially test targets that are used to measure print and/or proof attributes. Normally, but not always, it is printed in the trim area of the press sheet.Typical placement of a color bar on an offset press sheet - at the trailing edge (back end of the sheet).
However, it can take many different forms - sometimes hard to recognize - but always serving the same purpose.

Sometimes the "color bar" is incorporated within the graphic design of the publication. In this case the color makeup of the title (Cyan) and section headers (Blue, in this example, - Magenta overprinting Cyan).
Sometimes it is hidden in the spine (in this case the grey line running from top to bottom on the front edge of the photo).
While it is certainly possible to measure the color of the actual live image area, the technology is expensive and, as result, few printers are fortunate enough to have it at their disposal. Also, measuring the live image area doesn't provide as much useful information as a color bar can. Color bars therefore act as proxies, or substitutes, for the live image area as well as provide additional data.

The logic behind color bars

1) Unlike the live image area of the press sheet, color bars are consistent job to job. Therefore they are more efficient at providing a benchmark and can be used to track trends in variation over time.

2) Color bars can be tailored to meet the needs and measurement capabilities of individual print shops.

3) Color bars may be used to measure all aspects of the "print characteristic" - solid ink density, overprinting (ink trapping), dot gain, grey balance, as well as issues such as slur and dot doubling.

4) Color bars can reveal issues with ink hue, blanket condition, impression cylinder pressure, etc.

5) They can be used forensically to help understand why a specific job did not meet expectations.

6) They are efficient since, unlike the live image area, they are a constant made up of well defined elements that continue from proof to press sheet.

Solid ink density
A printing press is essentially a complex machine for laying down a specific film thickness of a specific color of ink onto a substrate. The ink is metered out in zones across the width of the press sheet according to how much ink coverage is required for each color in each zone.Therefore, for most press operators, the minimum requirement for a color bar is that it contains solid patches of the inks that will be printing since solid ink density is the only thing on press that an operator can adjust while the press is running.Those solid patches are then repeated over the width of the press sheet so that each ink zone is represented by at least one complete set of patches - containing one patch for each color being printed.
Information provided by only using solid ink density targets in the color bar
In this example, cyan is misregistered while the black printer is over emulsified (fountain solution breaking down the ink).
1) Provides a solid ink density value, measured using a densitometer, to determine if the press sheet is conforming to published industry, or shop specific targets.

2) Is an indirect, but practical, method of determining optimum ink film thickness and hence the balance of maximum color gamut without introducing image degrading inking issues such as slinging/misting.

3) The balance of the primary solid densities determines the hue of the overprints - i.e. the SID of magenta and SID of yellow determine the hue of the resulting red.

4) Indicate misregistration which can then be examined in the live image area.

5) Reveal defects such as slinging/misting/tailing, over emulsification, slur, doubling.

6) If records are kept, the hue of the ink currently on press compared with the hue of ink used in the past to determine if there is any contamination, change in color due to ink batch differences, etc.

Forensic targets on color bars are image elements that are typically not measured by the press operator unless there is a problem in aligning presswork to the proof. If that happens then these targets may provide useful information as to the cause of the problem.

Two-color overprint ink trapping targets
Ink "trap" is an objective indication of the ability, or inability, of a printed ink to accept the next ink printed compared with how well the substrate accepted that ink. Poor ink trapping results in presswork color shifts in reds (magenta plus yellow), greens (cyan plus yellow), and blues (cyan plus magenta) as well as a loss in total color gamut.
The two-color overprint solids allows for the objective measurement and evaluation of ink trap efficiency as well as the overprint hue error and greyness.
Typical trap values for three print conditions running a CMY ink sequence with Black first or last down:
Offset sheetfed: R=70, G=80, B=75
Heatset web offset (publications): R=70, G=87, B=72
Coldset web offset (newspaper): R=50, G=89, B=50

Slur and doubling targets
Slurring and doubling are print defects that occur when halftone dots and type blur as a result of a slight second contact or movement between press cylinders or the paper and blanket. (More about slur HERE and doubling HERE)
There are many different styles of slur and doubling detection targets. Here are two of the most popular:Of course, every halftone dot or letter character on the printed sheet will reveal slur and doubling, however the targets in the color bar signal the defect easier and quicker.
Grey balance targets
Grey balance targets are made up of a patch of three screened process colors that are balanced so as to appear as neutral grey under standard printing conditions. They are typically printed adjacent to a black screen tint of a similar value to allow for a quick visual, or measured, evaluation of how grey balance has shifted.Grey balance targets can be useful since variation in any of the three process colors because of dot gain, slur, doubling, density, trapping, and registration will be reflected by a shift in hue away from neutrality. The 3/C patch will take on a bluish, reddish, or greenish color cast.The idea behind this target is that any grey balance color shift away from neutrality suggests a possible color shift in the live image area. However, in production printing the grey balance target may not be a reliable indicator of presswork issues.

Other targets
Other targets that may be included in the color bar are:

Dot gainThese targets are intended to capture dot gain variation information. The dot gain targets may consist of just two patches for each process color to measure the dot gain a one location on the tone scale, or, with the addition of more patches, to measure the dot gain at the quarter, mid, and three-quarter tone values. Dot gain can be useful because issues like slur, doubling, or incorrect solid ink density, will be reflected by a variation in the measured dot gain.

Brown balance targets
Brown balance patches are similar to grey balance patches in function except that they are made up equal percentages of cyan, magenta, and yellow. Unlike grey balance patches which allow the press operator to make a subjective visual assessment of hue shift, brown balance patches can only be evaluated objectively with instruments.

ProprietaryProprietary targets such as that used by System Brunner are typically used to drive on-press closed loop color control systems.

Spot colorIf a spot or brand color is being used then it will warrant at least a solid patch in the color bar so that its solid ink density can be measured. Space permitting, the solid patch will be adjacent to a screened back patch so that dot gain information can be measured.

For process control, color bars should be included on every proof and press form of every job. If that is not possible because there is no room on the sheet (as often happens in newspaper work) then there are several options;

1) Run color bars on occasion by including it in the live image area.With the publisher's permission if required.

2) With the print buyer's permission, incorporate color bars test elements into the graphic/editorial design of the printed piece (see the USA Today example in Part 1).

Color bars are not a requirement for quality printing, however, they are key to making proofing and printing more efficient and effective while reducing overall production costs.

Presswork should be run "to the numbers" i.e. the solid ink density aim points, at which time the presswork should align to the signed-off proof. At that point the press operator should be free to make any needed ink key adjustments to refine the match. The color bar then becomes a record of initial match and needed adjustments. That information can be used in statistical process control to spot any trends, or issues, revealed by the kind of ink key moves that are made over time.

Color bars can be placed anywhere that they fit on the press form, including the lead and trailing edge as well as across the center of the form. In fact, placing it in the center of the form parallel to the inking rollers is ideal, since there is less likelihood of seeing the variation that occurs at the lead and trailing edges. Color bars can even be placed in the gutter inline with the direction of the sheet through the press, although doing so is not optimal since it provides information from only one ink key zone.

Ideally the color bar should use the same halftone screening as the live image area and have had the same press curve applied.

The issue of metamerism in print production

With print, each medium in the production process from original art to image capture, monitor display, proof, and final presswork has its own unique spectral characteristics. The majority of color reproductions utilize cyan, magenta, yellow, and black inks or colorants. But none of those inks are exact spectral matches to the media originally used to produce the original art. As a result, the inks used to create color reproductions are combined to simulate an artwork, but only under one industry standard light source - referred to as "D50" or "D65".

During production the integrity of the reproduction of artwork is monitored by making comparisons, for example, original to its copy or proof to presswork. The two colored objects are referred to as a metameric pair if they match under at least one combination of illuminant and observer and not match under at least one combination of illuminant and observer. They must also have different spectral response curves.

So, the phenomenon of metamerism begins with comparing a pair of colored objects. For example the color of the back door of this truck compared with the color of the rest of the truck.
In the truck example the pigments used in the paint were not the same for the back door compared with the rest of the truck. The two colors would have matched under the artificial lighting that was used when the door was painted. However, under sunlight conditions the door and body no longer match causing "metameric failure."

In this case metameric failure is a benefit to the prospective customer since it warned that the door was painted at a different time from the rest of the truck. Possibly it had been damaged and subsequently repaired. Unfortunately the effect of metameric failure in print production usually causes problems rather than benefits.

How metameric failure impacts print production

There are four types of metameric failure commonly encountered in print production.

Sample metameric failure This is the most common cause of color matching problems. The truck example above is an example of sample metamerism. Because proofs and press sheets form metameric pairs, this problem typically shows up when presswork matches the proof in the light booth at press but no longer match under the lighting conditions where the presswork will normally be used, e.g. a package in a store, or brochure in a home environment. Other examples of sample metameric failure include product samples (e.g. fabric) compared with their reproduction in proofs, presswork, or computer displays. Or process color screen tint builds. They may match under one lighting condition but not another. Sample metameric failure can also happen if two prints using very different technologies - such as offset print vs silkscreen print - are compared under different lighting conditions.

Observer metameric failure This can happen because of differences in color vision between observers. Although the common cause is colorblindness, it is not uncommon among "normal" observers. As a result, two spectrally dissimilar color surfaces may produce a color match for one person but fail to match when viewed by a another person. Observer metameric failure is the reason there were 31 individuals tested to derive the original 1931 "standard observer" values adopted by the ISO and that are still used today as the basis for the majority of color science.

Field-size metameric failure This occurs because the relative proportions of the three light sensitive cone types in the retina of the eye vary from the center of the visual field to the periphery. The result is that colors that match when viewed as very small, centrally fixated areas may appear different when presented as large color areas. This is the reason why color painted on a wall may appear different than the paint chip used to select the color even though they match when the chip is placed on the wall. In print production field-size metameric failure typically occurs when small PMS swatchbook samples are used to specify a PMS color that will cover a large press sheet area.

Geometric metameric failure Normally, material attributes such as translucency, gloss or surface texture are not considered in color matching. However here, identical colors appear different when viewed at different angles, distances, light positions, etc. Geometric metameric failure is most often seen when using metallic inks or paper, and specialty ink coatings or papers.

Tips for dealing with metameric failure

1. Be aware that it exists and may be the "simple" issue causing any color match issues.

2. If color needs to align across different lighting conditions choose pigments carefully or make the ink formulator aware of that requirement.

3. Control your lighting conditions - both for producing prints, final viewing (where possible), and for critical evaluation. The industry standard light source is referred to as "D50" or "D65" (5,000° Kelvin (North America), 6,500° (Europe).

4. Invest in PIA/GATF RHEM light indicators for everyone in the production chain that is involved in evaluating and approving color. RHEM light indicators are small (2" x 3/4") paper stickers with a unique printed design that uses metameric failure to indicate whether or not the viewing conditions are 5,000° K or not.Stripes appearing in the RHEM sticker indicate the lighting conditions and therefore whether a color evaluation can be made.
The stickers can be affixed to proofs or simply carried in a protective wrapper in purse or wallet.

5. Printshops should have viewing areas away from the press that allow print customers to view the presswork under typical lighting conditions (fluorescent and incandescent).

6. Be sure that all instruments (e.g. spectrophotomers) that are used for color evaluation are set to the same standard illuminant, D50 or D65, and same observer angle (typically 2°).

What is wrong with this scene?

Top reasons why color instruments don't agree

The increased use of instruments like spectrophotometers in the print industry has created an apparent increase in the level of precision in the measurement and description of color. However, the objective accuracy may not be as it seems - when comparing the measurement results from different instruments - even when coming from the same vendor.

Even when properly calibrated instruments can deliver different measurement values (>DeltaE 7 according to a PIA/GATF study) simply because of how the various instruments respond to the gloss on coated paper, aqueous coatings, UV coatings, and lamination. The use of UV cut filters (as is popular in Europe) can also increase the disagreement between instruments.

The top reasons why color instruments don't agree

• Variations in ambient conditions including instrument Induced sample heating resulting in "thermochromism" where Ink changes color due to a change in temperature and "hygrochromism" because humidity changes the way ink interacts with paper and hence its color.It's a good idea to record temperature and humidity levels whenever measurements are taken.

• Noise introduced by reflectometer instability, instrument and environment induced noise and dark current drift.

• Fluorescence in the substrate coupled with variation in the spectral power distribution of the instrument's illumination - too little or too much UV light.

• Instrument Geometry. There are typically no geometric tolerances on low end instruments. Fiber optic instruments tend to have wide geometric tolerances.

• Spectral bandwidth function may be too narrow or too broad and be too variable from wavelength to wavelength.
• No, or inadequate, black level adjustment. Non-black light trap or directionally sensitive light trap.

• Poor instrument maintenance.

• Infrequent or lack of recertification by factory. Lack of periodic verification

Tolerancing color in presswork - CIE L*a*b* and DeltaE

This method attempts to bring an objective, system independent, instrument-based method to color tolerancing. Because this method uses instruments to define colors, the range of tolerance and deviation from the target it is considered to be objective and unambiguous. It is much more sophisticated than the more subjective methods so far described in my other posts. As a result, a bit of background knowledge about color science is needed in order to understand how this system works and to understand its value and potential pitfalls.

A scientific approach to describing color
From a color science point of view, any color can be described by three basic attributes:

1) Lightness. This is the attribute of a color by virtue of which it is discernible as bright, dark, or somewhere between those extremes.
2) Chroma.This is the attribute of a color by virtue of which it is discernible as purity or intensity of color relative to a neutral color like grey. Also referred to as "saturation."
3) Hue. This is the attribute of a color by virtue of which it is discernible as red, green, etc., and which is dependent on its dominant wavelength, and independent of intensity or lightness.
So, from a scientific point of view, describing a color requires three values/numbers. One for Hue, one for Lightness, and one for Chroma.

Describing a specific color this way can be visualized as finding the location of a specific room in a building.One goes up a central elevator representing the range from neutral dark to light. Then one gets out of the elevator at a specific floor/specific lightness level and travels outward from neutral grey to an increasing amount of chroma/saturation as they move toward the outside edge of the building. Once they reach the desired amount of chroma/saturation one moves to the left or right to find the specific room/hue. So, directions to the specific room/color can be expressed as a recipe: Up X levels (lightness/floor level), Move X Distance (Chroma/Down hallway), Move X degrees (Hue/Along perimeter) = Room/Color.

This three coordinate method of describing a color can be visualized in cut-away form as in this graphic:In reality this 3D color space map is more complicated (you can see a movie of a real 3D color space HERE). However it should be good enough to explain this complex subject.

This three coordinate system (LCh) can then be used to map the location of a specific color.
Unfortunately, LCh has not been widely adopted to describe a color's location within a color space. Instead, the less intuitive L*a*b* notation is most commonly used. L*a*b*, more properly written CIE L*a*b* uses the same 3D model but identifies the color according to it's "L" lightness, "a*" axis value (+a* = more red, -a* = more green compared to neutral grey) and "b*" axis value (+b* = more yellow. -b* = more blue compared to neutral grey).

Defining a color location using CIE L*a*b* coordinates
Using the three coordinate CIE L*a*b* system allows us to numerically identify any color within a color space. In this example, I'll use a print color space and identify the desired color within that color space:
Tolerancing a color using CIE L*a*b*
Color tolerancing using CIE L*a*b* involves comparing the measurements, taken with a spectrophotometer, of a color sample (the output) to the data of a known color (the specification or input value). Then the "closeness" of the sample to the specification is determined. If the sample's measured data is not close enough to the requested color values, it is deemed to be unacceptable and adjustments to the process may be required.

The amount of "closeness" between two colors can be caluculated using a variety of methods. These methods calculate the distance between the two sets of measurement coordinates (e.g. CIE L*a*b* values) within the three dimensional color space. The size of the distance is defined by the size of the tolerance and is expressed as a "DeltaE" value (Delta Error).

To calculate the "closeness" of the specified color and the sampled color, the specified color is pinpointed by its position in CIEL*a*b* color space. Then a theoretical "tolerance sphere" is plotted around the color.The sphere, with the specified color at its center, represents the acceptable amount of difference between the specified color and other measured samples (the color output). The actual size of the tolerance sphere is determined by the customer's specification's for acceptable color difference. The tolerance value is expressed in delta (∆) units such as ∆E usually written as DeltaE (delta error). Measured data that falls within the tolerance sphere represents acceptable color.Measured data that falls outside the tolerance sphere represents unacceptable color.

Typical customer tolerances in the graphic arts industry usually range between 2 and 6 ∆E. This means, for example, that samples outside the tolerance sphere lie more than 6 ∆ units away from the specified color. Tolerances less than 2 ∆ units are typically unachievable given normal process variation. Differences between two colors that are up to 4 ∆ units away from each other are usually not visible to most viewers.

Issues, concerns, and caveats when using CIE L*a*b* DeltaE tolerancing
While this method can bring an objective and potentially unambiguous method to color tolerancing there are several issues to be aware of that can cause misunderstanding and error.

1) CIE L*a*b* DeltaE tolerancing is instrument dependent, however, different instruments can deliver different values from the same color sample.
Some of the reasons include: poor maintenance of instrumentation, infrequent recertification by the factory, lack of periodic verification, spectral bandwith differences, lack of geometric tolerances, variations in fluorescence in the substrate and instrument illuminant, instrument and environment induced noise, dark current drift, variations in ambient conditions, thermochromism (ink changes color due to a change in temperature), hygrochromism (humidity changes the way ink interacts with paper and hence its color).

2) CIE L*a*b* DeltaE values are dependent on the formula used - and there is no universally agreed standard for the formula that should be used.
Some formulas are: DeltaE 76 (sometimes referred simply as DeltaE), DeltaE 94, DeltaE 2000, and DeltaE CMC. In general, DeltaE 76 values are highest, DeltaE CMC values the lowest especially for saturated colors, DeltaE 94 and 2000 are lower than DeltaE 76 but higher than DeltaE CMC.

For example, these two color patches are made up with the indicated CIE L*a*b* values:The DeltaE difference between these two colors as reported by the different color difference formulas:
CIE 76: 7.10 (a large difference - unacceptable)
CIE 94: 1.51 (well within typically acceptable variation)
CIE 2000: 1.57 (well within typically acceptable variation)
CMC: 2.26 (within typically acceptable variation)

So, depending on the formula used to calculate the difference in color a measured sample may, or may not, be within acceptable tolerance.

3) It is harder to see the differences when colors are very saturated. It is easy to see a difference when colors are near neutral.
Formulas like CIE 94 attempt to compensate for this difference in visual color acuity, however, it is not the predominantly used formula. That honor goes to CIE 76. It's therefore important when discussing color variation to specify which formula is being used to calculate DeltaE values so that the numbers can be better interpreted.

4) The color performance of a system or press sheet is sometimes reduced to a single DeltaE value as a statement of being within tolerance. This can be very misleading since the single DeltaE value is an average of all sampled colors and will likely not reflect the performance of specific critical colors.
Statements such as "This press sheet is within 2 DeltaE of the proof" are virtually meaningless.

5) There are no CIE L*a*b* controls on a press.
If a color on a press sheet is out of DeltaE tolerance - the press operator effectively has to guess at what should be done to correct the problem using tools not designed for this function like solid ink density, water, impression pressure, etc. to effect a change in color.

Tolerancing color in presswork by eye

Once the press operator has achieved their solid ink density targets during make ready, they typically will do a visual examination to compare presswork color to proof to evaluate the closeness of the match. They will also do visual comparisons during the run to check the consistency of the match through the press run. Print buyers typically also do the same thing - relying on their eye for color to verify the match and consistency.
For most people in the graphic arts, the eye is the final arbitrator on the quality and consistency of presswork - however, this method has some limitations caused by the fact that the eye is part of a very tricky instrument: the human brain. For example, look carefully at this graphic containing light green and light blue swirls:
Light green and light blue?

Actually there are no light blue swirls, What you see as light blue is actually the same color as the green ones. They are both R 0, G 255, B 151. Cutting out a section of the "light blue" swirls and lining them up with the light green ones proves they are indeed the same color.This illusion is so strong that you might have to down load the image into PhotoShop and confirm it for yourself.

There are several characteristics of our eye/brains that can play tricks on our perception. Being aware of them will help you more clearly understand how your color perception can be mislead and hopefully provide a clearer view as to what you are actually seeing.

1) The eye/brain auto-white balances. The eye/brain selects an area that it "knows" is white - forces it to appear white and balances other colors accordingly. This is the trick that allows us to see a white paper as white with surrounding colors being natural under a variety of different colored lighting situations. This often causes problems with monitor proofs where an image should be "white" i.e. should result in no halftone dots in the presswork, but in fact has grey or even a color cast in it that results in dots being printed. The eye/brain sees the area as white when in fact it is not.

2) The eye/brain has no color memory. Not only does the eye/brain auto-white balance, it also rebalances color whenever you look from one object to another. This makes comparing two colors that are separated, by even a small distance, impossible. For example, in the below image, the press operator cannot effectively compare color between the image on his soft-proof with the color on his press sheet.
The only way to compare two colors is by cutting through one sample and overlaying it on a reference (e.g. cut press sheet over proof) like this:If the color aligns across the cut then you have a match.

3) The eye/brain cannot judge variation consistently. In order to tolerance acceptable color variation, for example custom/brand colors, you need to have a reference high/low density guide that provides an example of the two extremes that the color must fall within. Providing a swatch guide with holes through it as in this example:allows users to place the swatch over the press sheet to more easily confirm the color match as well as whether it falls between the two acceptable extremes.

4) The eye/brain's perception of color is influenced by the size of the area of color. This is one of the reasons that the paint color selected from a small paint chip seldom appears the same as the color once it's painted on the wall. The same issue happens when selecting a spot or brand color from a swatchbook. Always try to get a reference chip, draw down, or previously printed sample, that is as large as possible.

5) The eye/brain's perception of color difference is not uniform for all colors. It is difficult for the eye/brain to see differences in highly saturated colors. However, a small degree of variation is easily seen when colors are near neutral. Variations in the green part of the spectrum are more easily noticed than the same degree of variation in the red part of the spectrum.

Tolerancing color in presswork using solid ink density

Background information - ink film thickness & solid ink density

Offset printing presses are designed to lay down a film of ink, in the presence of water, onto a substrate - usually paper. The ink forms the image while the "water," more accurately fountain solution," prevents the non-image area on the printing plate from accepting ink. For the process to work, there needs to be a critical ink/water balance with the goal of having an ink film thickness between one micron.

If the ink film thickness is too great, the result can be "ink tailing/misting." In addition, the non-image background may take on ink resulting in "catch-up" (sometimes mistaken for "scumming"):
On the other hand, if the ink film thickness is too thin, the result can be a breakdown of the ink on the sheet causing low contrast, loss of sharpness, and mottle:
So, from a color tolerancing point of view, because the function of ink is to filter light and allow us to see color and because its thickness also effects the integrity of the printing process - ink film thickness on the sheet becomes an important metric to measure and tolerance in presswork.Top: CMYK at high ink film thickness/solid ink density.
Bottom: CMYK at low ink film thickness/solid ink density.
There is no practical way to directly measure the ink film thickness on a press sheet. However, there is an indirect way and that is to measure the solid ink density (SID) using an instrument called a densitometer.

Color tolerancing through densitometry

Measuring SIDs in the solid ink patches in the color bar with a densitometer does not actually provide information about the color being printed. However, because it indirectly provides information about ink film thickness (which impacts color and tone reproduction) SID values are valuable for process control and defining variation during a press run where the instrument, ink, and substrate remain the same.North American (Status-T) high-low specifications for acceptable SID variations measured with ink dry.
Top: Commercial sheetfed, Middle: Magazine/heatset web,
Bottom: Newsprint/coldset web.
From a color point of view, the assumption is that all three chromatic colors vary in the same direction and therefore remain in relative balance. When that happens there is a shift in color saturation (higher SIDs = higher saturation) as well as tone reproduction (higher SIDs = higher dot gain/TVI). If one color, e.g. Cyan, is at the maximum low point while another color, e.g. Magenta, is at the maximum high then the result may be a visible color bias in the presswork.
Typical SID variation in presswork graphed by measuring color bar patches every 10 sheets through the press run.
While a densitometer can also be used to monitor variations in non-process, i.e. spot/Pantone colors, usually a printed sample of the target color, including a high/low density tolerance reference, is used instead since this helps both print specifier and supplier visualize the acceptable range of color change as SIDs naturally vary during the press run.Checking for spot color variation
Addendum: Densitometer set up - "Status" condition

Densitometers are set by their manufacturers to an industry defined "Status" which defines the total response of the instrument including light source, optics, filtering, and receptor for given wavelength. The primary responses for the print business are "Status E" and "Status T" (ANSI PH2.18 and DIN 16536). In addition, densitometers are available with or without polarizing filters. Dry ink density readings from polarizing and unpolarized densitometers as well as those set to Status E vs Status T will not agree. Typically European instruments are set to Status E and use polarizing filters while North American instruments are set to Status T and do not use polarizing filters.

The important thing to be aware of is that if SID information is shared outside of the printshop - then the Status of the instruments that were used to determine SID values must be known. In addition, it is critical that all instruments within the printshop are set to the same Status. In North America, where many of the presses and their closed-loop color control systems are from Europe, it is not unusual to find the press set to Status E polarized while the handhelds are set to Status T unpolarized which can easily result in quite a bit of confusion in production.