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FLEXO Magazine : October 2011
trolled by plate curves at the RIP. These plate curves will differ, depending upon the anilox rolls and cell volume, ink viscosity and media or substrate that we will print upon. Much like our discussion on inkjet paper, the various media types on the press perform differently and must be controlled. The total ink limit of the digital file has to be controlled in the design or prepress area. BUILDING ICC PROFILES An ICC profile is a description of a device and its capabilities. Using the basics outlined earlier, each device and its variables must be optimized. Once the device and its variables are optimized, they must be maintained as closely as possible to that optimized condition. The premise of creating an ICC profile is very simple. For a scanner, you simply scan a known photographic target then compare it to a data refer- ence file. The data reference file is the measurement file describing the color patch information on the photographic target. The ICC profile creation software compares what you captured on the scanner to a data measurement file, or what the target actually is, then creates a fix to compensate for the difference. A digital camera profile is created in much the same way. A monitor profile is created by displaying a series of color patches on screen with an attached measurement device to capture the patches. Once again, the data refer- ence file contains the actual information of the patch set and the measurement of the screen is what is occurring. The ICC profile becomes the fix, so the monitor is capable of previewing digital information more accurately. A printer profile requires you to print a series of color patches then measure them with a spectrophotometer. Again, the data reference file describes the information that was sent to the printer, and the measurement file describes what was printed. In the case of printer profiles, we will be required to enter information regarding total ink limit and black generation. Black generation information relates to the black ink starting point, black ink end point, shape of the black curve and ration or removed cyan, magenta, and yellow ink to the amount of introduced black ink. Volumes can be written on black generation, so if you are not sure how to address this equation, make sure you ask an expert. The resulting profiles describe how your devices cap- ture, preview, and output color. HOW ICC WORKS In order to implement an ICC compli- ant workflow, we need ICC profiles, a color management method (CMM) and software to execute the color space transformation. At least two profiles are required for a color space transformation, but there are cases where three profiles can be used. For most workflows, we will require a source profile which describes what we want the image to look like, and a destination profile which describes where the image is going to. ICC pro- files are created with forward (A to B) and inverse (B to A) tables. The forward table works from the device color space to CIELAB and the inverse table works from CIELAB to the device color space (Illustration 1). Another option (Illustration 3) utilizes a source, destination, and a simulation profile. While there are several possible scenarios where this color space trans- formation can be applied, it is easiest to explain when images are RGB and are coming from the digital photographer. With ICC profiles and the tables understood, we can move to rendering intents. A rendering intent is used to de- fine the rules regarding color mapping from one color space to another. All color spaces are not created equal as we see in Illustration 2. The question is how to map these colors to create the illusion that we can do as much in print with approximately 6,000 colors as compared to the 16.7 million colors we can see. This is where the rendering intents come in. There are three rendering intents with a variation of the third. These rendering intents are perceptual, saturation, and colorimetric. The saturation rendering intent (Il- lustration 3a) is used for large format www.flexography.org october 2011 FLEXO 87 Harper has devoted an entire division to help flexographic printers and converters achieve unprecedented levels of consistency, quality and profitability. Using our exclusive SHarper SystemTM we eliminate variables that impact quality and increase predictability of press results. Call 800-438-3111 for a free copy. Smart. To learn more, call 704.588.3371 or Toll Free at 800.438 .3111 Or visit our website. Graphicsolutions DiVision harpE riM a GE.coM Americas • Europe • Asia ©2011 Color Management Conference FTA Ad.indd 1 9/23/11 2:14 PM