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FLEXO Magazine : October 2011
concept? Gaining the understanding of all of the color controls on our devices and how to utilize them to meet our expectations. COLOR CONTROLLING DEVICES Your workflow is made up of individ- ual pieces and parts. For example, the digital camera, scanner and monitor share quite a few similarities for setup and calibration. • A digital camera is calibrated for the scene, focal length and lighting by performing a white, gray and black balance. That calibration defines the dynamic range of that particular scene. • A scanner calibration is far easier to perform as the focal point (dis- tance to the content) does not change, nor does the light source. The dynamic range is set by scan- ning a grayscale card with white, black and gray. The settings are saved and used over and over again for all scans. A monitor is not much different. What is the white point, what is the black point, and where is the mid point? Dynamic range is the key to setting up these devices to optimize the capture and preview capabilities of the devices. Output devices are different and re- quire a little more thought and practice. In order to drive any of your output de- vices correctly, you will need a RIP. This software accepts the common file types created within the graphics industry and writes them to specific devices, such as an imagesetter, a computer-to-plate device, an inkjet printer, or a digital press or copier. In all cases, a calibration needs to be performed. The calibration optimizes the device in order to achieve the desired results. For the sake of our discussion, we will begin with an inkjet printer, after which we will discuss a printing press. A professional inkjet printer contains multiple ink cartridges containing differ- ent ink colors. The goal of these inks is to create a large color gamut. Depend- ing upon the intended use of the inkjet printer, we may have light inks which are intended to create very smooth tone distribution. Additional inks such as red, green, blue, white, metallic and the like are used to further expand the capabilities of the printer and to fill a more specific market need. To further muddy the waters, each type of inkjet media or paper is designed to perform a different task, based on price or performance. Media can change the output dramati- cally, therefore each media needs to be calibrated. The role of the RIP is to allow access to each and every one of the inks in order to optimize the capabilities of the ink and media combination. We should see controls for ink restrictions per channel, linearization, and ink limit- ing. Ink restrictions per channel are intended to restrict each of the primary ink colors (cyan, magenta, yellow, black, white, red, green, blue, metallic, etc) in order to create the largest us- able color gamut. Linearization controls are intended to create a smooth tone curve or dynamic range. This includes blending the light inks to create smooth, even steps through the range of colors from the smallest dot to the largest dot and then to the solid. Finally, the ink limit is defined to ensure that the shadow region creates a dark overprint without bleeding or puddling of ink.This process is performed for each resolution, droplet size, and type of media. As a reminder, when we print the same file on different devices we get dif- ferent results. When we print the same file on the same device with different media, we get different results. This concept must be addressed during the process of calibration, not the process of ICC profile creation. Now that we have a basic understanding of the calibration process on an inkjet printer, we can apply that understanding to the flexographic printing press. A flexographic printing press has far more variation and controls than an inkjet printer, but the premise follows similar lines. The ink restriction per channel is controlled by the anilox roller and volume of the cell, along with the viscosity of the ink. Linearization is con- www.flexography.org october 2011 FLEXO 85 Harper Anilox Roll Engineered for performance. Built to last. Guaranteed performance. From four locations across the globe. At Harper Corporation we do more than sell anilox rolls. We deliver confidence that comes with a 100% performance guarantee, backed by a team of graphic experts, and supported by a full compliment of products and accessories. With anilox roll manufacturing and restoration facilities in Charlotte, NC; Green Bay, WI; Herford Germany and Bangkok, Thailand; Harper Corporation delivers dependable consistency no matter where you print. To learn more, call 704.588.3371 or Toll Free at 800.438 .3111 Or visit our website. Anilox Roll Division HARPERi MAGE.Co M Americas • Europe • Asia ©2011