Troubleshooting Color: Output Color Profiles

More than once I have been asked: "OK, so the color is wrong, how do I make it right?"

Troubleshooting CMYK color can be a pain, because there are often many places the problem could be lurking, and changes made in one, may inadvertently alter the output based on info from another. So in this five part series, we will look at five important steps to troubleshooting a color managed system, or colorimetric tuning.

As you all know, a color management system is usually broken into five parts:

1. Source color space
2. Media parameter setup
3. Source color space designation
4. Output color profile
5. Output calibration set

Let's take a look at number four on our list - Output Profiles

One of the first things to be aware of is your own expectations. People often assume that printer profiles should make everything match but a printer profile is just a measurement of what a combination of printer, ink and paper can reproduce.

Different types of printers and ink sets will produce different color gamuts. Different papers and surface textures will influence both color gamut and appearance. Matte papers always look flatter than gloss papers for example. Also the color of the paper white has a big influence. A warmer paper color will give warmer grays and skin tones than a cooler more blue-ish white paper.

Media with Optical Brightening Agents (OBAs) often require custom profiles to account for the fluorescing factor.

The combination of the ICC output profile and the calibration set allow the RIP to adjust for the white point, imaging characteristics and d‐max capability of the output media. For standard color, the output profile may have less effect on color than does the calibration set and other factors described previously. Bypassing conversion always ignores output profiles.

In most cases, the standard Fiery output profiles for Plain, Coated Matte & Coated Gloss may be suitable for most customers on most media. These are based on GRACoL standard, therefore are neutral grey by default.

After machine setup and linearization, the machine should be calibrated on the target media and test prints made using the applicable standard Fiery profile. Only if results appear unacceptable or sub-optimal should the time be spent to create custom output profiles.

If a custom output profile is necessary, the standard 928 patch target seems to provide suitable results on most printer/copiers. I advocate the use of an iSisXL spectrophotometer to reduce the time and effort to read the test patch pages. Otherwise, an ES‐1000 or ES‐2000 can be used within a Fiery RIP, or an XRite spectrophotometer for external software, but of course, using a hand-held device takes more time.

In some cases, the profiles being used in Photoshop may not be the same as the profiles on the RIP controller. One example of this is if the USWebCoatedSWOP profile is being used in Fiery Creative Suite with a newer RIP controller that has the SWOP2006_Coated3 profile installed from the factory. In these cases, you may import the profile you are using for the working space definition in Creative Suite onto the RIP's controller so it is available in Color Setup.

Another example is if you are using a custom press profile for a conventional press and need to match the RIPs color output to that press.

If your inkjet is driven by RIP software then part of the calibration and profiling process is setting the printer options, ink limiting and linearization and it is with these that the root of most problems can be found. Getting the printer options right for any media can take a while, factors such as the number of passes, resolution, head height and drying times all can have a big influence on the print. Again the media manufacturer should be able to guide you.

Specific settings that may help:

Optimized: Creates custom calibration d‐max calibration targets as read from the profile test patch page(s). 
This setting should generally be left ON, which is the default for most printer/copiers. Only the d‐max endpoint is read from the target. The intermediate curve is calculated using a general formula and does not follow any unique density variations in the printer/copier.

Black Generation: Specifies toner limit and GCR parameters. 
Specifying a black toner maximum of 95% instead of the default 100% will provide a smoother tone and gloss generation in the deep shadows. If designated at 95%, TAC reaches a 180‐260% value in the shadows, while designating at 100% usually causes a TAC drop to about 130%. Using the 95% black specification prevents a gloss roll‐off in the shadows on some media, while using the 100% black specification may reduce total toner usage. 

95% is usually recommended for best image quality. A TAC (Toner Limit) value of 260% should be used. Default values for Ricoh printer/copiers in CPS Ver 3 and Ver 4 may default to either 400% or 270% dependent upon the revision. 

Very aggressive GCR settings may reduce banding and total toner usage dependent upon the colors found in the source job. Changes to other parameters may be used for specialized purposes.

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Do you have a color management question, horror story or event to share?

Email me at reilley4color@gmail.com

Troubleshooting Color: Source Colorspace Designation

More than once I have been asked: "OK, so the color is wrong, how do I make it right?"

Troubleshooting CMYK color can be a pain, because there are often many places the problem could be lurking, and changes made in one, may inadvertently alter the output based on info from another. So in this five part series, we will look at five important steps to troubleshooting a color managed system, or colorimetric tuning.

As you all know, a color management system is usually broken into five parts:

1. Source color space
2. Media parameter setup
3. Source color space designation
4. Output color profile
5. Output calibration set

As we have discussed, the source colorspace is crucial to determining how the system should translate from the input color to the output color, via command given to the rendering engine. Without knowing where you start from, it is difficult to navigate where you wish to be.

The color space and variant used to create the job must be designated in the RIP's job parameters. If you know with certainty the input color space, you can define it explicitly. If you do not have this information, most operators use sRGB, since it is the smallest of the RGB input color spaces, and thus the lowest common denominator.

Most RIPs allow you to recognize if a given file has input profile information embedded in the file. If present, this information gives you the best chance of output that matches what the file's creator intended.

Almost every file has some CM information present. Even if the original creator of the file was not prepress proficient, Adobe Creative Suite automatically embeds color input info when saving files. Should someone convert from RGB to CMYK in Photoshop, for example, the file is now in GRACoL CMYK, since that is Adobe's default. Honoring this embedded information is the best way to ensure you are printing to the original creator's intent. It is up to the operator to ensure that this embedded data gets honored.

The easiest and most consistent way to do this is the Use Embedded Profile When Present selection in the color setup tab of the job's parameters which is only effective when the job contains an embedded tag/profile. This is usually the first item to check when printed colors are significantly different than expectations. 

A few troubleshooting hints:

• AdobeRGB jobs printed as sRGB appear flat.
• sRGB jobs printed as AdobeRGB appear too dense with high chroma.
• Flesh tones in GRACol/SWOP jobs printed as ISO (System 7 default) appear rather sun burnt.

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Do you have a color management question, horror story or event to share?

Email me at reilley4color@gmail.com

Don "Hutch" Hutcheson Interview

With more than 41 years of experience in photography, design, prepress, printing, and color science, Don Hutcheson has pioneered many techniques we now take for granted, like RGB workflows, soft proofing, extended-gamut printing, and digital proofing.
In 1995 he started the world’s first color management consultancy, HutchColor, LLC, to bring the concept of ICC color management to professional graphic users. Today he continues to train the world’s top printers, publishers, agencies, photographers, and designers through private consulting and public conferences.
In 2006 as chair of the IDEAlliance GRACoL Committee, Hutcheson used his own proof-to-press calibration method (now known as “G7®”) to produce the current GRACoL and SWOP data sets. Since then G7 has made standardized printing and proofing easier and more accessible to thousands of printers and print buyers world-wide.

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CR:     Let’s start with a bit of history. How did you first come to be interested in digital color, and what kind of training prepared you for the career you now have?

DH:     Digital color is the child of desktop publishing, which evolved from electronic color scanning, which in turn evolved from graphic arts photography or “color separation” – one of the key enabling technologies in the development of color printing. Like all printing, digital color is therefore simply a form of photography, which has been my passion since I was 13, so its natural that I should be interested in it.

From 18 thru 22, I served a five-year apprenticeship as a graphic arts camera operator at a company called Photo Engravers, Ltd. In Auckland, New Zealand. When they bought one of NZ’s first electronic drum scanners – a Hell C-296, the union wanted it to fail and put me on it with nothing but a badly-translated German manual.

I twiddled every knob and made every mistake you can imagine, including one day removing all the unwanted inks and replacing them with black. When that job hit our 1-color proofing press a few days later, it was like nothing anyone had ever seen before and I was nearly skinned alive, until they added the black plate, when suddenly everything looked wonderful. Today we call that GCR.

Though designed for CMYK work, I saw the scanner’s photographic potential and found I could make just three RGB negatives and print them onto photo paper through RGB filters. With a little experimentation I was able to make prints that matched not only the color of an original transparency, but also the subtle highlight and shadow details with a level of perfection hitherto unobtainable by analog means.

Although the C-296 was not a digital scanner, it was my first experience of what we now call digital imaging and I’ve been hooked ever since.

CR:     Your career has spanned several decades – what are some of the technologies that have come and gone during that time?

DH:     Continuous-tone camera separations, direct-screening camera separations, tray development, nitrogen burst development, glass screens, contact screens, silver masking, tri-pack masking, double-overlay masking, wet etching (with potassium cyanide!), dry etching, film stripping, ruby masking, analog proofing (AgfaProof, DuPont Cromalin, DuPont WaterProof, 3M Color Key, Transfer Key, and MatchPrint, Remak, etc.), drum scanning – you name it.

CR:     Is there any technology or ideology that has faded from use that you might hope we re-discover? Or what might be the next bleeding edge tech in the world of color management?

DH:     I’ve always loved the early continuous-tone printing methods like Collotype, partly because there are no dots to interfere with fine image detail, but also for their purity of color. Halftone printing imposes some color space limitations that don’t exist in true continuous-tone printing, where ink film thickness is varied rather than dot size. If someone invents a practical way to print truly continuous-tone CMYK with offset or digital efficiency, it will have a dramatic impact on fine-art reproductions and expanded-gamut applications.

As for the bleeding edge of color management, today’s biggest challenge is the huge difference between the official D-50 illumination standard and the actual light sources in viewing and measuring equipment. Color management is based on the assumption that we can measure color as it is seen by the human eye, but we are far from achieving that to a high level of accuracy.

The problem lies in the D-50 standard itself, which defines the quality of “standard white light” as a graph of emitted energy vs. spectral wavelength. Unfortunately, the D-50 spectrum is based on hypothetical “daylight”, rather than any commercially-available light source, so D-50 can only be crudely approximated by today’s viewing and measuring equipment. This means certain inks, dyes, papers, etc. can measure quite differently than they appear in a so-called D-50 viewing booth, and often an excellent “measured match” (with effectively zero delta E) can look unacceptable visually, and vice-versa. This disconnect between the D-50 standard and real-world light sources becomes even more of a problem as the demand grows for ever-higher standards of measurable color accuracy.

The obvious solution is to replace the D-50 standard with the spectral curves of a commercially-available light source, such as the fluorescent tubes used in today’s viewing booths, or some new LED equivalent, but agreeing on a new light source is fraught with political, economic and patent issues. Meanwhile, there are work-arounds that can reduce or eliminate the problem, but because they deviate from the D-50 standard, they are difficult to implement en masse. The new M1 measuring standard solves part of the problem but is far from a complete solution, and has in many cases exacerbated, rather than reduced, the related problem of OBA-enhanced papers, which fluoresce under UV light.

CR:     Let us now discuss the G7 protocols and their evolution – can you walk us through some of the early days of G7?

DH:     Around 1980 I developed a simple way to calibrate a color scanner to match the tonality of one printing or proofing system on another. At the time, “Dot Gain” (now called “TVI”) was the accepted basis for press calibration, but I found that consistent dot gain failed to give consistent visual appearance with different press conditions or technologies, like offset and pre-press proofing.

To solve the problem, I developed a simple neutral density-based technique that achieved a perfect visual match on neutral grays, regardless of inks or technology. But if the dynamic ranges of two devices didn’t match, I had to tweak the graphs to meet at the shadow point, while keeping highlight regions identical. That “shadow compression-expansion” principle remains one of the key features of G7, and the technique I used back in 1980 is still alive today in the free G7 Graph Paper Method.

Fast-forward to the 1990s when CtP removed film from the plate making process and the question became “what do we calibrate?” Previously we linearized the scanner or film setter, but now you couldn’t do that. So I put my 1980’s method into an Excel spreadsheet that allowed any press to match the tonality and gray balance of any printing or proofing system, and called the process “P2P” for proof-to-press or press-to-proof.

In 2004 the GRACoL committee used the P2P process to help develop the new GRACoL 2006 color space. We followed all the ISO 12647-2 rules except the obsolete TVI curves, which we replaced with NPDC (Neutral Print Density Curves) averaged from a number of ISO-standard press runs made with un-calibrated plates. The same shadow-weighted algorithm from 1980 was used to adjust the NPDC curves in shadow areas to fit any printer’s dynamic range, while preserving crucial highlight tonality.

To standardize gray balance, we followed the logic of the ICC’s relative colorimetric rendering intent, defining CMY gray balance as a function of paper color, reduced in proportion to dot percentage. This also mimics the human visual system’s “chromatic adaptation” phenomenon, and a camera’s auto white balance function.

GRACoL2006 and its sister SWOP2006 color spaces were wildly successful but to our surprise, many people were more interested in the P2P calibration method, so I donated it to Idealliance who re-named it “G7”, and the rest is history.

CR:     You encountered a lot of resistance initially. Can you give us some insight as to what that was like?

DH:     A fundamental rule of science is that any new discovery should be challenged rigorously. And a fundamental law of human nature is to resist change for change’s sake. So it’s not surprising that some industry experts and associations with a vested interest in the old TVI calibration method did their best to kill G7.

The main opponents to G7 were FOGRA, ECI and BVDM – three German associations roughly equivalent to Idealliance, that do great work in promoting standardized printing in Europe.

In 2005 I offered the P2P system freely to FOGRA and ECI, and suggested they partner with Idealliance in its development. But the request went unanswered until January 2006, when they announced their PSO certification system, which had been developed in secret while G7 was an open, public project.

PSO is based rigidly on the ISO 12647-2 standard, with emphasis on TVI curves, while G7 exposes the weaknesses of TVI and provides a more effective alternative. G7 was obviously seen as a threat to the revenue potential of PSO, but the PSO program could easily have replaced TVI with G7, or offered the option of TVI or G7. Instead those organizations refused to acknowledge G7’s many benefits, and took instead an aggressive public stance against G7, Idealliance and myself personally.

The good news is that ten years later, G7 has been far more successful than PSO, largely because it works more effectively, is far less expensive and can be used on any printing system, not just offset. There are now hundreds of G7 Master sites and thousands more unregistered users world-wide. In fact many German and European printers and print buyers have secretly adopted G7 – they just don’t advertise it.

CR:     When did you know that G7 was going to become the de facto standard?

DH:     As soon as we released GRACoL2006, it became obvious that much of its appeal was in the G7 calibration process. In 2006, Idealliance provided the G7 How-To and GRACoL and SWOP profiles freely, with thousands of downloads in the first few weeks. Printers all over the world began praising G7 as the first really useful calibration system they’d ever tried, even if they weren’t printing to GRACoL. Other processes like Flexo, screen, xerography, gravure, etc. also adopted G7 because it made life easier – especially when they had to come as close as possible to a GRACoL proof without the benefit of ICC color management.

CR:     What are some misconceptions some folks might have about adjusting color through grays?

DH:     The most common misunderstanding about G7 is that it’s a replacement for ICC color management, which is not true. G7 uses just four one-dimensional curves to achieve good gray balance and tonality, much as a photograph’s exposure and color balance problems can be “corrected” in Photoshop with RGB curves alone. When grays are corrected, colors are moved in the right direction, but may fall short of complete accuracy depending on additional factors that cannot be corrected with simple 1-D curves, like ink hue, trapping and opacity.

By contrast, ICC color management uses more complex n-dimensional Look-Up Tables (LUTs) to apply hue, saturation and lightness changes discretely to different colors. G7 generally does a better job on neutral grays, however, and provides several additional benefits, so the best of both worlds is to use a combination of G7 plus ICC.

CR:     Is there any color device that cannot be brought to G7 standard?

DH:     No, but systems that don’t have user-programmable 1-D LUTs may not be compatible with the G7 calibration method. In those cases, ICC profiles can simulate a G7-based color space like GRACoL, with the same visual effect, but without the special benefits of separate G7 calibration.

CR:     Are there any particular books, white papers, YouTube channels or other reference sources you might recommend to color management beginners?

DH:     One of the earliest but still one of the best books on color management is Real-WorldColor Management by Fraser, Murphy and Bunting. For color geeks, I recommend Measuring Color by R. W. Hunt. The annual PIA Color conference (www.cmc.printing.org) is another excellent color management learning resource.

CR:     What are you working on now? How’s it going?

DH:     As a photographer, one of my life-long passions has been “expanded gamut” printing, i.e. getting more color out of conventional printing to make it look more like photography. My most recent efforts in that regard contributed to the new Idealliance XCMYK color space and methodology, which is based on maximizing the color gamut of four-color offset and can be simulated on any digital color system with sufficient gamut. In 2017 Idealliance will extend that work to consolidate and standardize both 4-color and 7-color expanded gamut strategies, ink sets and workflows.

CR:     I know you are a great lover of IPA’s. Got a favorite, and why?

DH:     America is blessed with the greatest selection of micro-breweries in the world. The beer I drink most often is Dale’s Pale Ale, whose red, white and blue can prevents oxidation by light. Dale’s has an excellent balance of hops without the excessive alcohol levels that spoil so many IPAs. Other good brews include Sierra Nevada, Anchor Steam, Lagunitas, Stone, and many others.

Many, many thanks to Don for taking time out of his busy schedule to speak with us.

To see and hear Don speak about the G7 protocols, as they apply to wide format printing, click HERE.

Check our Definitions page for many of the terms used above.

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Do you have a color management question, horror story or event to share?

Email me at reilley4color@gmail.com

Troubleshooting Color: Media Parameter Setup

More than once I have been asked: "OK, so the color is wrong, how do I make it right?"

Troubleshooting CMYK color can be a pain, because there are often many places the problem could be lurking, and changes made in one, may inadvertently alter the output based on info from another. So in this five part series, we will look at five important steps to troubleshooting a color managed system, or colorimetric tuning.

As you all know, a color management system is usually broken into five parts:

1. Source color space
2. Media parameter setup
3. Source color space designation
4. Output color profile
5. Output calibration set

Part 2 - Media Parameter Setup

There are many different kinds of paper, such as recycled and rag paper for newspapers, glossy coated paper for magazines, uncoated paper for stationary and bright-white coated paper for high-quality brochures. Some paper is coated for a particular ink, some has already been printed on (shells) and some is in fact black, or darkly opaque for printing on a 5th color station press, using white toner. And now synthetics have become a hot trend in digital printing.

As you can imagine, each type has different characteristics when it comes to printing. The recycled paper sucks up more ink, and if you don’t take this into account, your beautiful full-color photos will become too dark, and the ink will blur over the paper, creating an ugly brownish effect. Coated paper reflects light differently, and distinction between matte & gloss can make a LOT of difference to the final colors.

So, how do you optimize artwork for all of these different kinds of papers? Well, that’s the easy part. 

Standard CMYK inks have been tested on every type of paper imaginable. The way cyan, magenta, yellow and black are printed on a specific type of paper is documented in an ICC profile (a complete record of a print device's color gamut). All you need to do is download these free “Color Profiles” and select the right one when you export a PDF using InDesign (Export → Output → Color Conversion & Destination). 

In Photoshop you can use these profiles as input profiles, to soft-proof colors printed on specific stock.

To learn more about profiling, read Calibration and Profiling

The RIP's job parameters related to media setup and imaging style must be consistent for the customer’s job, as well as for the related profile generation and calibration pages. 

A specific determining factor is Fuser temperature: Higher fuser temperature results in increases in gloss and density.

The primary specification for fuser temperature is Paper Weight, with a lesser degree of control through paper type (Plain, Glossy, Matte). Fuser Nip (dwell) and direct Fuser Temperature setting in the paper catalog entry also have an effect on fuser temperature.

Halftone Mode: Also known as screening type. Specifies whether line or dot screening is used, and in
some print devices, the halftone resolution (lpi) and native resolution (600 or 1200).

Resolution: Effective pixel addressability, collected pixel size and gray tone possibilities. May be
specified combined with Halftone Mode.

These job properties must be decided upon prior to any further color tuning, and used for all customer
jobs, calibration sheets and profile targets for the applicable job/media setup. Of course, any given
machine and customer may use one or more job/media setup with varying parameters.

Any adjustments determined in Print Engine Setup should be applied via SP mode and/or a paper
catalog entry and used for all applicable prints.

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Do you have a color management question, horror story or event to share?

Email me at reilley4color@gmail.com

Troubleshooting Color: Source Color Space

More than once I have been asked: "OK, so the color is wrong, how do I make it right?"

Troubleshooting CMYK color can be a pain, because there are often many places the problem could be lurking, and changes made in one, may inadvertently alter the output based on info from another. So in this five part series, we will look at five important steps to troubleshooting a color managed system, or colorimetric tuning.

As you all know, a color management system is usually broken into five parts:

1. Source color space
2. Media parameter setup
3. Source color space designation
4. Output color profile
5. Output calibration set

Part 1 - Source Color Space

Color files set up to be printed always use a color space, even when the exact color space is not known by the customer. In general, the source color space is either RGB or CMYK, and composed pages are often found to contain both. For most customers, RGB is preferred, since it offers a larger color gamut, and higher saturation levels.

RGB usually comes in one of two flavors: sRBG or AdobeRGB. The key difference is in the size of the gamut, with sRGB having a smaller gamut than AdobeRGB.

Any work produced on a Windows device will usually be in sRGB by default. RGB is usually preferred since most sources (scanners and digital cameras) generate RGB, and most display screens use RGB as a native representation.

Some customers use CMYK as a source color space, with many flavors possible; SWOP, GRACol, ISO, etc., each with multiple variants. (See the Definitions page for definitions of these and other terms) The CMYK color spaces are usually characterized by the achievable gamut of a certain printing technology (ink and press type) on a certain class of media. While designing in RGB offers more possibilities, designing in CMYK often assures the final output will be within gamut.

The CMYK source space may also be used to emulate the lowest common denominator of two or more digital printers/copiers when matching output between the multiple printers/copiers. 

In any case, the source color space and variant must be known for optimum output color. 

A tag or profile is frequently embedded into the source file to identify the color space being used. The tag may be directly read in the RIP's job parameters.  Embedded profiles, if present, should ALWAYS be honored.

If the source color space is not known or discernable, experimentation must be used to find the closest match.

Other parameters specified in the Source area of the RIP job setup pertaining to color are:

• Almost always leave at the Full Output GCR default, allowing GCR parameters in the output ICC profile to specify black channel generation. Setting this parameter to Full Source GCR5 may cause color translation problems and should be avoided.
• Rendering Intent : Usually set to Relative Colorimetric which assures maximum colorimetric accuracy of in‐gamut colors. The default Presentation designation increases chroma of many in‐gamut colors, often rendering them inaccurate. 
• Photographic (Perceptual) also changes many in‐gamut colors, but may be useful if the shadows tend to block‐up.

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Do you have a color management question, horror story or event to share?

Email me at reilley4color@gmail.com

GCR (Gray Component Replacement)

Experts agree that in color reproduction black can be beautiful if used wisely. Black can add details and contrast in the reproduction which is impossible to achieve with the three process colors. However, if the black is not used judiciously, it will do more harm than good. It will make the colors look dirty and create an unnatural contrast.

— Dr. R. K. Molla

Reseparating customer supplied files is rapidly gaing popularity with printers and publishers as a way to lower print manufacturing costs. Reseperating allows for greater control of the final output, including specific filtering for media, color management, and finishing options.

Although the application is not limited to specific print market segments - these are the ones that are most quickly adopting this technology:

• Newspaper publishers
• Insert and flyer printers
• Magazine publishers
• Catalogers
• Directory printers

Within the CMY color space, a range of colors can be achieved by combining the three primaries. This combination in its turn can be thought of as a hue component (which will require a maximum of two primary colors) and a grey component (a mixture of all three, in an appropriate quantity to give the required saturation). If the grey component is replaced by black ink, the same color is being achieved by using two primaries and black. The act of substituting a quantity of black for the grey component is known as "Grey Component Replacement" (GCR).

GCR is also termed "achromatic color removal."

In grey component replacement (GCR), contrary to under color removal (UCR), the CMY values that add to grey all along the tone scale can be replaced with black ink. UCR only adds black to the CMY equivalent of what would have printed as a grey or near-grey.

Although there are many benefits to reseparating customer supplied files in order to use GCR, the most promoted and fairly easy to justify is in regards to reduced ink usage - typically suggested as a savings of around 20% in CMY inks with an increase of about 6% in K ink used while maintaining the same visual appearance in presswork.

Based on that figure, calculating a return on investment seems fairly straight forward. For example - based on the industry average of ink consumption for a sheetfed printer being about 2% of their gross earnings, a $10 million dollar a year printer will spend $200,000 a year on ink. If they reduce their ink usage by 20% they will save about $40,000 a year in ink costs. Theoretically, if the printshop spent $10,000 on a reseparation solution their payback time would be just three months and they will have saved $30,000 in the first year of implementation - a very good investment.

This is the removal of the gray components of the three colors and replacing them with black.

In GCR reproduction, all the primary and secondary colors remain the same as the normal chromatic reproduction, however, the blackening effects by the tertiary colors along with the gray components of the other two colors are removed and replaced with black. 

Various percentages of GCR can be applied to the separation for economical reasons and visually more pleasing results. The black dot sizes are increased to replace the gray component that has been reduced in the process colors. If 100 percent GCR were used, every color area in the reproduction might contain dots of only black and two or three process color inks. 

Commonly used percentages are 50% to 75% GCR. The goal of GCR is more consistent color, increased detail in the shadows, shorter press makeready, and possible ink savings.

Advantage: GCR results in less ink being used, and some of that ink is black which is normally cheaper than the others.

Advantage: The areas where less ink is used are regions of high ink use, so the potential for drying and offset problems is reduced.

Advantage: The resulting output is less susceptible to changes in the printing variables since you are not continually trying to balance as much C, M, and Y.

Because a GCR separation uses a non-chromatic color – black – throughout the tonal range and reduces the proportion of C, M, and Y in the mid- and quarter tones, the color in GCR separated images is more stable as solid C, M, and Y ink densities naturally vary through a press run. Note, however, that the added stability means less ability for the press operator to move color if required. For many printers, the increased color stability is a perfect compliment to the industry trend for a “by the numbers” print manufacturing process.

Other advantages:

• Reduced make-ready times/faster start-ups/less wastage
• Harmonized separations enhance press form printability
• Reduced fan-out or web growth
• Dramatic improvement of image appearance when slight press misregistration occurs
• Reduced drying times
• Higher printing speeds
• Improved repeatability of print jobs
• Grey balance within images is more stable


Disadvantages of GCR include:

GCR may reduce the ability to adjust some colors.

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Do you have a color management question, horror story or event to share?
Email me at reilley4color@gmail.com

Munsell Hue Circle

“Popular color names are incongruous, irrational, and often ludicrous.” – Albert Munsell

This is from the opening of Munsell's own color blog, which defines the Hue Circle.

Hue is the quality by which we distinguish one color from another, as a red from a yellow, a green from a blue. In science it can be measured and identified by its position within the visible spectrum. It is one of the three components that computers use to define color: hue, saturation, & value (chroma).

On the Munsell Hue circle, there are 5 Principal hues: Red (R), Yellow (Y), Green (G), Blue (B), Purple (P) and 5 Intermediate hues: Yellow-Red (YR), Green-Yellow (GY), Blue-Green (BG), Purple-Blue (PB), Red-Purple (RP).

When a color is void of hue it is called a Neutral, such as Neutral Gray or Neutral Black. On the Munsell Hue circle it is an axis in the middle (N).

Each of the 10 Hues (both principal + intermediate) are then further subdivided into 10. As you move clockwise around the circle the 5 of each Hue is the principal center of that color family, while the 10 of each Hue is considered the intermediate. Even finer distinctions can be made between similar Hues through the use of decimals.

The Munsell Color Order System is a way of precisely specifying colors and showing the relationships among color based on a three-dimensional model.

The primary hues in the RGB or CMYK models are shown around the Munsell Hue circle to show how they relate to the Munsell Principal and Intermediate colors.

RGB & Hue
Red, Green, and Blue are the primary colors for this additive color model in which red, green, and blue light are added together in various ways to reproduce a broad array of colors. Equal amounts of RGB = White.

CMY(K) & Hue
Cyan, Magenta, Yellow, and Black are the primary colors used in printing for full-color documents. Mixing varied percentages of of these four inks reproduce colors. Equal amounts of CMY minus Black (K) = Dark Brown.

A Munsell Notation is always written in a specific order as a fraction.

For example: 5R 5/5

5R = Red HUE at step 5

5/ = a VALUE step of 5

/5 = a CHROMA step of 5

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Black Point Compensation

One area that many who are new to color management are still questioning is the role of Black Point Compensation in several of the dialog boxes in Photoshop.

Black Point Compensation can be used when transforming files using ICC profiles. An example would be converting from RGB to CMYK. The conversion process using ICC profiles requires a source (where is the file coming from) and a destination (where is the file going).

Due to the fact that there is no standard technique in how ICC profiles map pure black from the source to the destination, there are cases where the pure black of the source profile can be a different value than the black of the destination profile. In some such cases, unacceptable results can develop when the file is output.

In order to correct these possible problems, Adobe introduced a feature in Photoshop 5.0 called Black Point Compensation.  (BPC)

When this option is checked, Photoshop examines the black points of both profiles to see if each will work in harmony. This is the case where the black mapping of both profiles is such that an accurate black is represented in the final output.

Upon examining both profiles, if the black levels are going to produce acceptable results, the transformation from source to destination profile is carried out. If upon examining the two profiles, Photoshop sees that the two black points are different, an extra processing step is carried to ensure that the black point of the source profile is correctly mapped to the black point of the destination profile.

In rare cases using Black Point Compensation can cause unacceptable results and the effect is usually washed out detail in the very dark regions of the final image.

In our experience this problem usually rears its ugly head with older RGB output profiles.

Adobe recommends, and we agree, that in almost all cases, Black Point Compensation should be on when dealing with CMYK files (doing RGB to CMYK conversions or CMYK to CMYK conversions).

In most cases, doing RGB to RGB conversions with Black Point Compensation will produce desirable prints. However, depending on the profile, doing a conversion from RGB to RGB with Black Point Compensation can produce poor output with washed out blacks.

It appears that this problem with older RGB profiles is dependent on the software that is used to generate the profile. Apparently there is a “Black Tag” feature in ICC profiles that in some cases can be used or unused depending on the software that actually creates the profile. For this reason, there is no hard and fast rule that says we should or should not use Black Point Compensation with RGB output.

Our recommendation is to use Black Point Compensation with RGB output profiles or if possible, try a test with Black Point Compensation on and off. BPC will either produce acceptable results or do nothing when using modern profiles.

There is one other case where you may want to turn off Black Point Compensation.

When you want to soft proof output for a printer that has a low dynamic range like newspaper, where the blacks are usually not very dense.

By turning off the Black Point Compensation, the soft proof is more accurate in predicating the effect of this low dynamic range. Black Point Compensation should be turned off in the CMYK Set-Up.

A few points about Black Point Compensation (BPC) to remember:

• BPC is always on for perceptual rendering intent, i.e., the checkbox setting has no effect. 
• BPC can be turned on or off for (Relative) Colorimetric and Saturation rendering intents.
• BPC is always off for Absolute (Colorimetric) rendering intent.

Input density is derived from pixel levels in the image file.

Output density is derived from the printer profiles.

In a printer that could reproduce infinitely deep black tones, output density would track input density all the way down to zero. But real-world printers cannot print any darker than a maximum density, which is called Dmax. 

Dmax is a function of the paper surface and the type and amount of ink. 

Glossy or semigloss papers tend to have higher values of Dmax (2 or higher) than matte (fine art) papers (typically around 1.6-1.7). 

Black point compensation specifies the printers behavior around Dmax.

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Paper is the 5th Color

Paper is an analog variable in the world of digital printing. It directly affects the hue in the highlights,  it affects the entire color gamut size for the print job, has a powerful impact on shadows, and is often outside the control of the production workflow.

While many people believe that traditional color management is about managing the CMYK inks and their separations, paper has as much of an influence on the color of the final printed piece as it does on the mechanical and chemical action of the inks or toners. Although a given paper brand’s attributes may be consistent, paper characteristics are not standardized. There is variation in attributes between mills as well as variation around an attribute property from a given mill. Paper is considered a commodity but its properties are a long way from standardized.

A lot has changed in the world of paper. One of the biggest changes in recent years has been the increased use of optical brightening agents (OBAs) in many papers to give the appearance of a very bright white paper. Printers have been known to accuse paper companies of using cheaper goods and “cheating” by using optical brighteners.

The initial choices made on paper selection might not take into consideration the impact later in the production chain, and sometimes those decisions can have unintended consequences.

White papers are not RGB 255,255,255. Paper companies control the shade of their papers by adding dyes and other chemicals to affect appearance. More dyes, less reflection, more color compensation. The paper owns some of the color space so detail that requires paper’s hue cannot be reproduced. The recent trends toward blue white papers have resulted in more and more dyes in the paper and further deviations from neutral. Some of today’s papers are equivalent to a 3 percent cyan screen.

Modern color management solutions do allow you to bias your results to either a strictly neutral result with no consideration of paper color, or to neutrality based on the paper color.

This can be very important, as the human eye will quickly key in on the “white” of the paper and judge other colors on the paper based on that shade.

Paper shade, or white point, is the key attribute of paper and is measured using L*a*b* based on CIE XYZ. Described by these three values, color management applications calculate complex color inter- pretations to characterize paper and predict paper’s effect on color reproduction.

OBAs are used to increase the apparent brightness and whiteness of papers and their use is becoming more prevalent in paper manufacturing. They increase brightness and whiteness by absorbing energy in the ultra violet and emitting (fluoresce) the energy in the blue area of the visible spectrum. Because, to the eye, blue/white looks "whiter" than yellow/white OBAs are not really whiteners, but bluing agents. OBAs are also used in ink to expand gamut or brighten 4/C image printed on poor substrates - e.g. newsprint.


While it is not practical for printers to quantitively measure the OBA content of the materials that they use, it is quite an easy matter to qualitatively see the OBA content. All it takes is an inexpensive (less than $15 USD) "black light."

For example, with the black light it is easy to see that the paper used for the Pantone Goe system swatch book (on the left in the image below) contains more OBAs than the conventional Pantone spot color swatchbook on the right. Also, it's clear that the uncoated paper section in the Pantone spot color swatchbook contains more OBAs than the coated section.

Viewed in light that has an ultraviolet component, the papers appear bright and blue. They have an apparent expanded gamut. However, the printed hues will mutate, or change color depending on the light source. This effect is called metamerism and drives a need for light booths and an understanding of the viewing conditions when color matching or judging color. Simply put, printed hues shift, particularly in the highlight tones, when papers contain optical brighteners.

In reality, the rise in the use of brighteners can be attributed to a host of reasons, including production efficiency for maintaining a consistent look to a paper with changing content and a desire from customers for a brighter sheet at lower cost.

Another, more subtle problem can be the intended colorcast of the sheet. While in some ways we might consider OBAs an unintended colorcast, designers will sometimes purposefully choose a paper that has a colorcast.

The inks that are typically used in four color process printing block, to varying degrees, the fluorescence in papers containing OBAs. Black and magenta block the greatest amount, yellow a lesser amount, and cyan ink least of all. What this means is that when an image is printed using a halftone screen, lighter/pastel tones allow more more of the brightening and color shift of OBAs (towards blue) than the shadows. Color is effectively skewed towards the blue from shadows to highlights – but only when the paper being printed on has a high OBA content.

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Maintaining proper viewing conditions for print evaluations is a key part of color management.

The standards for viewing booths have changed over the past couple of years with the most recent release of ISO 3664 Graphic technology and photography — Viewing conditions.

If paper contains optical brighteners, color matching must be done in reference light conditions. When proofing on job stock that contains optical brighteners, it is important to critically examine both separations and curve effectiveness in the cyan containing highlight areas. The cyan/yellow color balance is hardest to achieve with these papers.

Even proofing papers contain optical brighteners. Creating profiles on these papers requires interpretation and tweaking if the press papers have a different level of optical brighteners or if the press papers have no optical brighteners.

Finally, optically brightened papers lose their fluorescence over time especially if exposed to light. The paper yellows. Print hues shift. Once printed, there is no recovery of the original paper whiteness so this should be kept in mind when a job reprints. Trying to match a first printing several months after completion is almost impossible. New proofs are a minimum requirement.

What additional tools can color management bring to the table to help tame the paper problem?

Traditionally, the way to “solve” OBA problems was to ignore them, primarily by using a filter that cut the UV light to stop it from hitting the paper and thus prevented the brightening effect of the OBAs. This is still a very effective approach to process control, but it is no longer the norm in color management. The other way we ignored it was by doing just that, not acknowledging the problem.

Today, we are much more likely to solve the OBA problem by quantifying the amount of OBA by including the UV in the measurement and then adjusting the ICC profile to compensate for its presence. Some recent color solutions provide Optical Brightener Correction (OBC) technology, which allows you to fine tune the profile results by evaluating specific test charts against a series of Munsell color standards in the target viewing condition. This combination of physical standards and measured results allows for a uniquely precise correction for optical brighteners.

An additional parameter that can be handled in color management is the final viewing environment. Traditionally, a graphic arts workflow targets a daylight illuminant (usually noted as D50/2 – describing the illumination and viewing angle). One additional way to fine-tune the result is to define the viewing condition of the final destination or illumination at the intended point of use if it is not D50.

This can be done by either using CIE defined illuminants or by actually measuring the lighting in the final environment.

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And what about Glossy Paper?

Paper gloss is related to surface roughness and therefore affects color reproduction. Light of all wavelengths is reflected from the surface of paper. How it is reflected defines both its gloss and dot gain characteristics.  

If the paper is glossy and smooth, it scatters less light and there is less dot gain. Light is reflected almost like a mirror (specular reflection). 

Matte, dull and uncoated papers scatter more light resulting in more dot gain. Also, these papers require more ink to achieve a given density further increasing the dot gain. 

Papers from different manufacturers absorb ink and toner/developer solution differently. There is no overall standard for surface roughness, ink absorptivity or developer absorptivity within the paper classification scheme. For the most accurate color, press profiles should be made on the chosen stock for a particular job. 

Matte and uncoated papers are even more variable.

The best color reproduction will occur on:

• Bright papers with uniform spectral reflection;
• Papers that are smooth and glossy;
• Papers that are neutral in shade; and
• Papers that exhibit minimal fluorescence.

One curve for all paper surfaces leads to less than optimum color.

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Do you have a color management question, horror story or event to share?

Email me at reilley4color@gmail.com