Color Management and the Harlequin RIP

For many years, the Harlequin RIP has had the ability to apply various forms of color management while processing files. However, understanding and using the color management capability properly has been a bit of a mystery. The RIP’s instruction manual describes the functionality of each setting but it won’t advise you why one setting will serve you better than the next.

Further, worthwhile guidance requires a deeper understanding of color management in general and there isn’t enough room or enough time to address the entire topic in a single article. Therefore, what we will try to do instead is give you a good foundation for understanding color management in general and some pointers for using it in the Harlequin RIP specifically with ink jet color proofers.

In the printing industry, color management describes a series of processes and tools designed to help provide predictable and controllable color output across several devices that print in color. For example, an ink jet proofer may be sold to emulate (or predict) the final output of a job printed on a press. Herein lays problem number one. A press uses cyan (C), magenta (M), yellow (Y), and black (K) ink. An ink jet proofer may use between seven and eight colors that include the CMYK inks plus lighter variants of each.

Plus, the inks used in the proofer are not the same composition of inks used on press, and the paper stock used by the two processes are rarely the same. This means that, under normal circumstances and with no help from “color management,” a printing job sent to the proofer can rarely predict accurately how the job will look once it’s printed on press. Quite often, the result is simply a “pretty picture.”

Compounding the issue is the common misstatement that “my proof should match my press.” We all understand what we want as an end result (predictable color) but this is a treacherous statement. The proper description is that the proof should accurately predict what the press is capable of printing so that the pressman has a solid target with which to work. This, in turn, may also serve as an example for the customer to approve and serves as “proof” of what the printer has contracted to perform.

As an example, it might be good to reminisce about older methods such as 3M’s MatchPrint or DuPont Chromalin. If a press sheet didn’t match the proof, it was most likely a matter of bad film, plates, or ink control. No shop would call 3M and ask them to change the colorants of the MatchPrint stock to match their press. Regardless, it’s very common in today’s parlance to say, “I want my proof to match my press.”

Getting back to our discussion, why do the number of inks, ink composition and variable stocks matter? Because of one important term: “Gamut.” Gamut is the scientific description of the range of colors a device is capable of producing. This range can be increased or decreased depending on paper stocks, number of inks, ink contamination and printing process. In short, the number of colors printable on press is different than the number of colors printable on an ink jet printer. Herein lays problem number two.

To get an ink jet plotter to accurately predict the results of a job printed on press, its gamut must be restricted from printing all the colors it is capable of producing. This is where color management comes in; color management and a little thing called process control.

Simply defined, process control is printing by the numbers. Densitometric measurements are taken at each step of the printing process; film imaging, plate imaging, printing on press. (You knew those color bars had a purpose beyond the pressman eyeballing them.) By verifying the accuracy of the process, printed color is predictable on a very consistent basis. Color management and process control are inextricably joined when it comes to creating predictable color because one cannot work without the other. Many have tried; many have produced less than optimal results. Why? Think about it. If you go to the trouble of using measurement tools to produce gamut-defining profiles for your proofer but fail to use the same tools during the printing process, how can you expect the results to appear similar?

So what does this process look like, and how does it apply to your RIP? Let’s take a quick tour.

On the proofer side, users output predefined test patches of various colors and tints from color management software. These patches contain color values known to the software package. Upon completion of output, the operator measures the patches (usually with a spectrodensitometer) and tells the software what the actual readings (values) are on that particular paper stock. The software uses the differences between the values to correct the color by writing the information into a “profile.”

Users can create different profiles for different stocks as well as different printers. However, the point is the same for each; instruct the system how to print to known values. (More on profiles later. . .)

On the pre-press/press side, very similar actions take place. Exposure values are first calculated to determine the proper settings for the media. Operators then send a series of test tints with known values to the imagesetter or platesetter. The operator measures the media and inputs the results to the RIP. At that point, whenever they send a job through the system, they get the results they expect - as long as all the measurement points remain the same. (Part of process control is maintaining the calculations through consistent monitoring. For instance, if the chemistry in the processor gets weak, the exposures may be incorrect and the tints may no longer reflect the proper values. This is why process control is so tightly tied to color management.)

Operators can carry this measurement process all the way out to the press if they desire. The same test sheets can be run on press and measurements taken for accuracy. Again, it’s important to note that unless measurements are taken during each press run, accuracy and predictability can slip.

So now you have the proofer outputting known values for the proofer, and you have the press outputting known values for the press. You’re all set, right? Wrong, of course. The two devices operate in different gamuts, remember? We now have to tell the proofer that we want to restrict its gamut to that of the press.

Let’s look at how color management is used in the Harlequin RIP, specifically for controlling color proofer output. Note: color management is a chargeable option for the Harlequin RIP. If you don’t have it or want to use the try-before-you-buy version, contact your dealer.

The easiest way to use color management with a proofer is to start by choosing a paper that has already been profiled (fingerprinted) by the RIP supplier. If you choose a pre-profiled paper, it becomes possible, using a simple “calibration” technique, to adjust your specific proofer to print in the manner expected by the RIP. However, it is important not to skip the calibration and to follow the calibration technique exactly. If you don’t, you cannot rely on the results.

First, configure a Page Setup for the proofer and verify connectivity and output with the plug-in.

Next, choose the proper paper in the ProofReady pull down menu. If this is not chosen properly, the calibration will be incorrect and the RIP will not correctly apply color management control. Note that resolution may be important when choosing the paper. If this is the case, ensure that your output resolution matches the resolution specified in the paper’s ProofReady profile.

After properly configuring the Page Setup, run a calibration strip using that Page Setup. Measure the calibration strip and proceed to the Calibration Manager to enter the values. As a side note, you might want to check out the Genlin Tool located within the RIP application folder. You should also take a quick look at Appendix C of the Navigator Reference Manual to see how you can use Genlin to automate the measuring process.

While in the calibration window, make sure that you choose the proper paper profile at the top of the window in the Profile pull-down menu.

Do not choose “Linear” from the Profile pull down menu. Linear is used when calibrating film and plates because the goal for film and plate output is a controlled “Linear” reproduction of the requested dots. That is, a request for a 30% dot should result in a 30% dot on film or plate.

Here, you are trying to get your printer back to the calibrated state contained within the provided profile. In other words you are trying to match the color gamut of the printer used to create the vendor-provided profile so that the ICC profile sitting on top of that will have an honest chance of being meaningful. When calibrating color proofers the goal is not to reproduce the exact dot percentage but to reproduce the proper color. Since the proofers use high-end “dispersed” screening, dot percentage isn’t important, proper tint reproduction is.

Enter the readings from your calibration strip and save the calibration. The RIP will use this information to adjust your specific proofer to run within the parameters of the proofer that was used to make the paper profile. That is, rather than fingerprinting your proofer, this allows the RIP to adjust your proofer to run according to the fingerprint of the goal proofer used by the RIP supplier.

After completing this process, return to your Page Setup and select the calibration you just made in the Calibration pull-down menu. This instructs your device to run in a known and controlled state that will best reproduce the items sent to it. Next, you will choose an industry standard default emulation. This means the RIP will restrict all color jobs processed through the Page Setup within the gamut of that standard. My advice is to start with SWOP (Specifications Web Offset Publications).

Why SWOP? First, the process control parameters for SWOP and Sheet Fed presses are not that different from one another (see industry standards for ink density, total dot gain, etc.), and second, a sheet fed press can meet or exceed the expectations presented in a SWOP-based proof.

By offering an “out-of-the-box” configuration based on a known and verifiable industry standard, the Harlequin RIP eliminates the need to go through the expense and down time associated with independently profiling (fingerprinting) equipment. Rather than trying to create proofs that are based on the fingerprint of a press that may or may not be conforming to process control standards at the time the fingerprint is made, a verifiable industry standard proof seeks to bring the press run into conformity with those standards which have been recognized as the best way to reproduce offset color. Note that this does not absolve you from using process control throughout!

What if you absolutely don’t want SWOP as your standard for proof output? Then there are two options. One, which I will not discuss in depth, is to have your press fingerprinted – but for the sake of all things good make sure it is running to industry standard specifications and follow all process control procedures when you make your profile. Or two (and I suggest this is the better option), set the RIP up to use a sheet fed press industry standard.

Before you make this decision, I highly recommend you try following the above procedures and produce a proof using the out-of-the-box settings. We use this process on a regular basis to test proofers and the results are very consistent and very closely match a certified SWOP press sheet we keep for comparison. Still, it’s important to remember the proof is a target for the pressman; a predictor of expected results when all procedures are followed.

The process for changing the emulation standard is as follows:

After completing all the calibration procedures outlined above (these won’t change because they only apply to the paper and the proofer not press output), proceed to the Color Setup Manager and choose “New ‘ColorPro’ Setup.”

In the New Color Setup window under Input Profiles\ CMYK Data, choose a sheet fed press profile such as “Commercial A.”

From the Output Profile pull-down menu, choose the paper you are using and for which you have already calibrated.

It is very important to leave the Output Emulation pull-down menu set to “None.”

Perhaps this is a good place for an explanation. And, though I can go into the reasons for these settings in some detail I will try and restrain myself to a paragraph or two.

While it is fair to assume the press profile should be selected in the “Output Emulation” pull-down menu, because of the way the RIP processes profiles it is more efficient to select it under the Input Profile: CMYK data pull down menu. Why? The RIP translates all color items into the specified color space at one of three points during the RIPing process: when the file first arrives, during the emulation phase and/or in preparation for the output device.

Since, in the vast majority of cases, the user will not have a profile for the scanner/camera that created the input – often because the input is from different sources – it will not be possible to enter legitimate values for the Input Profiles. But, by selecting the press profile in the Input Profiles pull down menu, the RIP immediately places the job into the press gamut. At that point, it needs only one more process to adjust it for proofer output; the Output Profile.

If you didn’t understand that, it’s OK for now. Just remember to put the press profile in the Input Profiles: CMYK data pull-down and use the proper paper profile for the Output Profile pull down menu and you will be fine.

The last things I want to discuss in the New Color Setup window are the Output Rendering Intents. There are a number of standard intents available. While their names may differ somewhat, their basic functionality will be the same.

There are four types of rendering intents: Absolute Colorimetric, Relative Colorimetric, Perceptual and Saturation. The generic description and use of each is as follows:

Perceptual: Used to create the best looking (but not necessarily accurate) reproduction of photographic images. Colors that are out of gamut and in gamut are moved relative to each other to maintain the perceptual difference between colors.

Saturation: Used to create the brightest (most pop) reproduction of flat tint color graphics.

Relative Colorimetric: Used to create the most accurate reproduction of colors. Colors within the gamut are unchanged, while all out of gamut colors are mapped to the outer edge of the gamut. The output white point is left unchanged regardless of the white point in the original image. Paper color is not simulated.

Absolute Colorimetric: Used to create the most accurate reproduction of colors. Colors within the gamut are unchanged, while all out of gamut colors are mapped to the outer edge of the gamut. The output white point will be changed as specified by the original image. The color of the paper in the press profile will be simulated by a flood of background colorant.

As a place to start, I would recommend you try Perceptual and Relative Colorimetric. If you need to add a background color (one found in the press profile, not the image to be processed) there is a “Simulate paper color of job” check box available. The rest of the settings I will leave for you to read about in the manual or try on your own.

After some experimentation and comparison, you should be able to determine quite quickly which steps and settings you’ll need to incorporate for best results. For some, it may require fingerprinting and profiling all the way to the press with stringent process controls at every turn. For others, a standardized set-up to SWOP, FOGRA, or Commercial A might be fine. Regardless, the RIP has the capability to understand and translate your various color needs if you have the inclination to work with it.

Further, there are one or two little-known tools available that, used properly, can help you take your RIP to the next level of color control. Complete with ink limiting capability and gray balance control, you might even want to use these tools to create profiles . . . but that’s a whole different article for next time.