The Mighty Colorbar: Take Advantage of It

By Ron Ellis

 


 How many things can you do to improve production that don’t incur an additional cost? One of the most important diagnostic tools I use in my daily work appears on almost every sheet I see – it is the colorbar. Color bars come in many different configurations. They may be homemade, provided by the press manufacturer, or copied out of a program like Preps. Some are simple and simply display density, while others display much more information. No matter what type of printing you do you most likely some type of colorbar on your sheet. Very often I notice is that the many printers are not using colorbars to their advantage. The colorbar can provide you with a wealth of information.

            The colorbar is a snapshot of the pressrun. When I talk with a customer experiencing a printing issue, the colorbar can tell the entire story of the print run – that is if the colorbar is properly designed. A good colorbar can tell if the sheet is at the same density of course – but we can learn much more about how that press is printing.

            Of course the most fundamental use of the colorbar is to measure density but even this is often foiled. Often prepress may be placing generic colorbars grabbed from applications such as Preps, or other sources. Very often these generic colorbars don’t provide the very information that is most important to the press operator. A good colorbar should have a measurement patch for each ink key for each color. This means the press operator should be able to lay the sheet down and measure the colorbar above each key so they can see how to move the keys. To do this you can measure the ink keys, getting the width and number of keys themselves so that you can construct a colorbar that contains information the press operator can use for each key.

            In addition the basic solid marks, the color bar can be used to give us much more information. Tints can give us information about how the press us printing. In a tint we can gain a snapshot of reproduction on the press during the job. First we can see the dot gain we on press during the run, which can be used to tell of if printing conditions on that individual cylinder have changed. In addition we can use the tint to see the reproduction of the dot, and the check for issues such as slur and doubling. A quick glance at the tints can tell us if we have printing problems, and measuring it can tell us if press conditions have changed, and if so on which units. While a 50% tint is helpful, it is even better if we can include a quartertone and ¾ tone. While space on colorbar is limited it is not necessary or often even possible to have tints for every ink key. In many color bars that I use the tints follow the solids, with a different tint value and color following each CMYK solid, and repeating across the sheet until all the colors and  tint combinations have been covered.

            What other information is important. Just from looking at the solids we can tell if the ink has changed. Being able to read and understand the LAB values of the ink at a known density is helpful, and it is easy to detect changes in ink (such as cutting, contamination, or material issues). In real life it is easy to track issues with ink variation based on knowing how that ink performs. If the ink changes at the same density then we know that the ink has changed. In the past this has been useful in detecting both ink issues such as inconsistent ink supplied by vendors, as well as contamination or ink changes that happen due to speed, heat chemistry or other factors in the production run.  In addition to the LAB values of the solids, the overprint patches are also important. By looking at the values of the patches, and knowing the reference values of these patches we can tell a great deal about how the inks are trapping and if there is a trapping issue, as well as if we will be able to match proofs and previous jobs. LAB is the coordinate grid system for mapping color, and by using it like a GPS it helps us to use our colorbars to tell exactly where we are. If we don’t have the ink on the page then we can’t tell what’s going on.

            When using a calibration method such as G7 or even just for proof matching the gray scale patches can also be important. While it is difficult in many production environments to use gray balance for production runs, it is still a good diagnostic and especially in operationts using G7 calibration the gray balance patches are important. Simply measuring the HR patch can provide a snapshot of what is going on with all the other patches. Even if you are running purely by eye a glance at the grayscale patches can provide you with some quick insight into what is going on with the job. ?

            How do colorbars impact my life as a consultant? Many of my customers call me and by looking at their colorbars we can often tell what has happened and changed in their production process. During the past year when we were working on test forms for GRACoL some of the experts we interviewed told us they almost didn’t need a special test form – that they could tell almost everything they need to know by looking at the colorbar. When you are trying to tell what is going on in your pressroom the colorbar in one important piece of data that you can use to see what is going on. It tells the whole story of your sheets – and it can save you time and money. 



 Ron Ellis is a Boston-based consultant specializing in color management, worflow integration, and press calibration. He has provided installation and training services to dealers, manufacturers, and content creators since 1986. An IDEAlliance G7 Expert and chair of the GRACoL Committee, Ron has performed over 100 G7 calibrations. In addition to calibrating pressrooms for customers such as Pantone, Ron also specializes in creating internal working spaces for brands and agencies that allow them to work more efficiently with vendors, saving both time and money. Ron is published frequently in industry magazines, and has produced training materials for numerous printing industry vendors and publishers. He can be contacted at 603-498-4553 or through his web site at www.ronellisconsulting.com.



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