3.01.2018

Why Does My Pure Black Print Out as CMY?

Why Does My Pure Black Print Out as CMY?

I recently had a customer call me in because he was puzzling over an unusual color problem - His print file specified pure K at over 95%, but the color management engine kept printing the file in CMY, and he could not determine why. It shared space with other color images, and their color specs had not changed at all, only the black image.

After some testing - OK, it was four and half hours of testing - we determined that it was the GCR causing the issue.

For those of you just joining the conversation, GCR is Gray Component Replacement. We discussed it previously HERE. You can also find it in the GLOSSARY.

Normally, we think of GCR replacing the CMY components of an image with more K to minimize the ink or toner usage. But under certain circumstances the GCR component of your RIP can actually add CMY to pure black if it determines that black alone cannot accurately reproduce the color relative to its original colorspace.

The certain circumstances are these: You ARE set to Full GCR (whether source or output directed) and you do NOT set your gray setting to include Text/Graphics/Images.

This can also be overcome by using pure primaries, which effectively turns GCR off.

RIP manufacturers have confirmed this is how the RIP is supposed to function, so this is not a bug, just a particular parameter setting that created a condition noticed only because were looking for it.


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

1.04.2018

CxF: Color eXchange File format

CxF: Color eXchange File format


If you work with color, you will be learning more about CxF, (Color eXchange Format) the new, open-source, XML-based, universal standard for color specification. It will re-define some aspects of our job.

It was approved by the ISO in June of 2015, but is now hitting it's stride.

Here is the definition, as written by X-Rite, who proposed and championed the new standard:
"CxF is a new standard allowing seamless, worldwide, digital communication of all commercially significant aspects of color. Furthermore, CxF is defined in a completely open way so that all aspects of a color can be communicated, even when the application and the color communication features required are unknown. For example, every software vendor implementing / supporting CxF is able to extend the information set to the needs of a new application without affecting the general usability. Wherever color communication is mission-critical, CxF should be considered the communication solution of choice " 
"Typically, color communication is done today using colorimetric measurement values such as CIE-Lab, XYZ, RGB, density, CMYK, or spectral measurement values. These values are often communicated in proprietary formats that don’t provide for meaningful communication outside of a narrow use." 
"In general, it is not sufficient to communicate a color recipe, a reflectance curve, or a CIE-Lab value. Depending on the application there are specific needs in the way a color should be communicated. A universal color communication language must be open –to describe and communicate such known and even new, as-yet undefined effects. In addition, this language needs to be able to bridge the gap from one industry to another. Depending on the application, further attributes need to be assigned to spot colors. Among the infinite list of possible attributes assigned to spot colors are serial numbers, part numbers, color mixtures, price of pigments, light resistance of the color, descriptions, application notes, comments, and many more. "
Spot colors, or “named” colors are created in the design process to provide a specific visual color for a given name on a given substrate. The process of rendering spot/named colors on different output devices is challenging due to:
  • Differences between different print technologies (colorants, screening, tonality)
  • Differences related to substrates
  • Differences related to different ink companies and formulations
  • Differences related to different tonalities on different print technologies
  • Differences related to different measurement devices, and conditions
  • Differences related to different lighting conditions
  • Differences related to overprint on white vs black vs another ink
  • And more…

CxF/X4 was created to solve the problem of not getting an accurate/desired spot colors when printing on different devices, and not being able to accurately proof.

It has since become an improvement over the previous standard/
ISO 17972 defines methods for the use of CxF3 to exchange measurement data and associated metadata within the graphics industry.
  • CxF3 (ISO 17972-1) This format provides prepress digital data exchange and verification for 4 color process printing.
  • CxF/X2 (ISO 17972-2) This format defines the CustomResource within the CxF/X structure for the creation of scanner target data
  • CxF/X3 (ISO 17972-3) This format defines the output target data within the CxF/X structure for the creation of output printer target data
  • CxF/X4 (ISO 17972-4) This format defines the exchanging spot color characterization data within the CxF/X structure

CXF/X4 was developed to help address these issues related to Spot/Named color workflows.


Implementing CxF

In order to make CxF/X4 work in your environment, you need to have the 5 C’s of Color Control

  • Color Capture device appropriate to the substrates being used in your process
  • Calibrated output devices which render color consistently within the page and between pages
  • Characterization of the actual spot/named colors for the given substrates being imaged (CxF/X4)
  • Conversion which recognizes the CxF/X4 tags embedded in the PDF in order to convert to different print conditions (including proofing) accurately
  • Conformance which allows you tosses the print and compare to the Reference color to determine if it's within desired expectations of color tolerance.

1. Determine the appropriate Color Measurement device:

Ensure measurement device is appropriate for given substrate, a 45/0 is appropriate for measuring on paper and similar substrates where the light from instrument is reflected at a predicted 45 degrees angle, but it is not appropriate when printing on substrates that have a metallic quality which will scatter the ancient light at different angles other than 45 degrees.

Understand that no two instruments measure the same way and that when multiple instruments are using in a workflow, that the color conformance between them has to be calculated before implementation, or you could find yourself beyond your tolerances before you start. 

2. Calibrate output devices

Obviously, for precise and accurate color reproduction, it is required to have output devices that can image color well within the customers' expectations for color tolerance. 

3. Characterization
Similar to how CMYK ICC Profiling defines the characterization data set of how a given set of inks/screening/tonality/substrate/print device will render color, we need a characterization data set of how a given spot/named color will render color for a given set of inks/screening/tonality/substrate/print devices. 

This characterization data set is created by printing tints of the desired color over white and black ink and on a given substrate (this quantifies the opacity of the ink, which is a major variable related to color reproduction). This requires printing the required color and measuring in the result. Once we have a characterization data set, we now can predict how this named color will react when exposed to different variables such as different substrates, print devices, lighting and mixing with other inks.

Again, similar to ICC Profiles, once you have your desired CxF/X4 characterization data for your given color, now you can provide a color palette to designers so they can more accurately see the results of this color when used in an actual design.


4. Conversion of the CxF/X4 data for different processes

Also, similar to ICC Profiles, CxF/X4 characterization data can be used to physically convert the color to different print conditions and accurately represent the original intent (assuming the output device has sufficient gamut to simulate the desired named color. 

This is critical for proofing the color to simulate what it will actually look like on the final device.

This CxF/X4 data can be used in an ink formulation system to automatically generate a new ink which will share the same spectral properties for devices that can’t use the same ink that the original definition was created for. For instance, Offset versus Screen print inks.

5. Conformance to assure the printed result will meet customer expectations

Again, similar to using ICC Profiles to assess the conformance of CMYK output, the Conformance can be assured by using the CxF/X4 data as the reference and assessing if the reproduction of the desired named color matches within defined tolerances.

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CfX contains meta-data specifications for a number of print variables, including, but not limited to:

Substrate types:
Coated Paper
Uncoated Paper
Cardboard
Glossy White Film
Transparent Film
Metallic Film
Transparent Film (reverse)
Leather
Metal
Paint
Paper
Plastic
Textile
Tile
Vinyl
Wood
Ceramic
Other

Background:
Substrate,
Process_Black,
Other.

Surface Finish:
None
Gloss Laminated
Matt Laminated
Gloss Varnished
Matt Varnished
Other

Print Process:
ElectroInk
Electrophotography
Flexography
Rotogravure
InkJet
Offset Lithography
ScreenPrinting
Other
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Also from X-Rite, the go-to CFX resource page, with links to the ISO docs, and other resources:

https://www.xrite.com/page/cxf-color-exchange-format

Here is a cool webinar video that explains and explores the format:

https://vimeo.com/138970501

And here is a link to a "What They Think" article:

http://whattheythink.com/articles/74283-cxf3-color-management-exciting-things-come/

The International Color Consortium (ICC) has praised the new format as an excellent way to spec spot colors:

http://www.color.org/CxF_test.xalter

We currently work in CGATS format, so here is a nifty online converter that may be helpful:

http://www.jpereira.net/apps/cxf2cgats/




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

7.16.2017

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

5.01.2017

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

1.29.2017

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.

----------------

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

1.04.2017

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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10.31.2016

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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10.03.2016

Closed Loop Color

CLOSED LOOP COLOR

Before digital color management became the rigorous science that we currently use, print professional all had a bag of tricks to get their desired color results from a given printer. They had experimented, suffered, worked around and generally gotten to know their print device, warts and all, in order to get what they wanted from. Things got considerably more complicated when another device, like a scanner, or wide format printer was part of the mix.

Then when they got a new device, they had to start over from scratch.

This was Closed Loop color management, a tight bond between user and device.

Open Loop color management, however uses the "Universal Translator" concept, going from the input color start point color space (usually RGB of some kind) to L*a*b* color space - which is based on human vision, and a larger color space than any digital device - then from L*a*b* to CMYK+, according to the device profile of the printer. This allows users to plug new equipment into the mix without having to change color management setting for any other device. Essentially, it takes the input of any color space, then translates that to the output gamut of the print device.

As a method of color management, closed loop color is usually considered a mistake. However, some higher end production printers use Close Loop Color Control (CLC) to ensure color fidelity throughout a print run. The two concepts are very different.

Closed loop color is essentially an on-press feedback system that scans and measures the color bar on the moving paper (web or sheetfed) -- while the press is in operation -- and then feeds this information back to the press console to make automatic adjustments. When the color information recorded across the sheet: the ink density (or ink film thickness, and amount of light reflected off the press sheet) and the spectrophotometric data (or measurement of the hue of the ink) deviate from the specified levels, the closed loop system automatically adjusts the press to bring the color back to its target.

Why is this important? More and more presses include such measuring devices to ensure that the color you specify within your design application (InDesign, Quark, Photoshop) can be carried consistently from your computer to the printer's proofing devices and then on to the pressroom. This is also called color management.

So, remember the difference - the closed loop color management system is archaic and inadequate to modern CM needs, while closed loop control control is a breakthrough of technology that allows a digital press to maintain color throughout a lengthy print run.
n addition to color fidelity, additional benefits of closed loop color include reduced make-ready times, reduced paper waste and ink consumption, and the ability to save ink-presets for later use (i.e., to record all color information in the press console for later replication in future jobs).


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8.05.2016

How Color Print Tricks the Eye


Consider for a moment the marvel that is color printing.

It uses a scientific trick of lightwaves - Metamerism - plus engineering marvels that electrostatically charge a piece of media in very specific places, then release precisely placed, incredibly small grains of colored toner, and a developer fluid that reacts with the fuser's heat to bond those particles, all to trick your eye into thinking that a reflective surface is an emitting surface.

Hundreds of times a minute.

Or spray micro-drops of ink from two directions at once as the media rolls by.

And the controlled combination of colored toners or inks trick our eyes into interpreting a reflective surface as if it were an emitting surface. This is a trick worthy of magic, but really, it's science.

Here is a basic explanation of the color spaces involved with printing.

Simply put, the Cyan, Magenta and Yellow printing inks cancel out the Red, Green & Blue wavelengths of light coming to our eyes from the media's surface, metamerizing the wavelengths, tricking our biological processor into thinking it is the RGB of our human color vision.

Why red, green and blue? You may remember from science lessons in school - visible light is a spectrum of light, described as frequencies, ranging from reds through the colors of the rainbow into blues and purples.

From a scientific point of view, light can be a mixture of any of those monochromes, light of a single frequency.

However, we have light-sensing cells called cones in the retina of our eyes to detect the amount of light in the red, green and blue areas of the spectrum. Because of this, “true” monochromatic yellow light, which lies between red and green on the spectrum, is indistinguishable from a mixture of monochromatic red and green light.

From a design point of view, since we can’t perceive the difference, it simply does not matter, and so we can abstract any color we can see as a mixture of red, green and blue.

The science of digital color, however, describes color using the L*a*b* color model, among others, which is a bit less intuitive but more closely approximates how the human visual system works.

It uses the Lightness values of an image (the grayscale version) as an axis to rotate opposing poles of chromacity described as a* (red vs green) and b* (yellow vs blue) to describe the gamut of human color vision.

“But wait," I hear you cry, “You just told us human eyes sense red, green and blue!” That is true, it’s called the Trichromatic model of vision, and while it describes how the individual cones in the eye work, it doesn’t accurately describe the visual system as a whole.

Separating the human perception of lightness from color leaves the a & b dimensions as measures of chromaticity, brightness independent of color. This is important, as some colors appear brighter or darker, despite being at the same intensity.

For instance, we see a fully saturated yellow as a lot brighter than a fully saturated blue.

Regarding ranges, L is measured from 0 (dark) to 100 (light), a from -120 (red) to +120 (green), and b from +120 (yellow) to -120 (blue).

So let's look at the rods and cones mentioned above.

Human color vision takes place in the retina, and ends deep in the brains 's visual pathways.

The ventral stream (purple) is important in color recognition. The dorsal stream (green) is also shown. They originate from a common source in the visual cortex.

The retina is the innermost of three tissue layers that make up the eye. The outermost layer, called the sclera, is what gives most of the eyeball its white color. The cornea is also a part of the outer layer.

The middle layer between the retina and sclera is called the choroid. The choroid contains blood vessels that supply the retina with nutrients and oxygen and remove its waste products.

Embedded in the retina are millions of light sensitive cells, which come in two main varieties: rods and cones.

Rods are used for monochrome vision in poor light, while cones are used for color and for the detection of fine detail. Cones are packed into a part of the retina directly behind the retina called the fovea, which is responsible for sharp central vision.

When light strikes either the rods or the cones of the retina, it's converted into an electric signal that is relayed to the brain via the optic nerve. The brain then translates the electrical signals into the images a person sees.


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7.13.2016

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