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FLEXO Magazine : June 2008
TECHNOLOGIES & TECHNIQUES Banding has occurred from the use of a tint across a large area. Limit your use of tints to smaller areas to reduce the chance of this. transparent in order to blend with the other colors of the process, thus on its own lacks visual density. As mentioned before, using this technique on small text or a barcode is not recommended. OFF SCREEN Understand that gradients, blends and vignettes are more dif- ficult for a flexographic press to reproduce than your computer monitor. Printed gradients can often show undesirable lines known to the industry as banding, or chattering. A good printer will know how to minimize that effect, but there are things the designer can do to help. Usually, a shorter range of tones in a gradient equates to more banding. If at all possible, try to use a greater range of tones in a gradient. Because some platemak- ing processes cannot produce very small dots, it is advisable to have the lightest part of your gradient a 3-percent tone or higher. Also, adding just a touch of noise to your gradient by way of a Photoshop filter can help prevent banding. The next thing to do is properly prepare the halftone images for flexographic printing. Having an open and communicative re- lationship with your printer and prepress vendor makes the pro- cess much easier. Find out what line screen Qpi) your plates will be imaged in, so you can use the proper resolution. Line screen refers to how many rows of dots will be used to render your art. This is important because a quality halftone image should have twice the PPI (pixels per inch) as it does Ipi. If plates will be im- aged at lSOlpi, your halftone images should be at least 300PPI. Unfortunately, not everyone always uses that rule. If an im- age does not have enough resolution, it will look pixelated when printed. It's easy to make that mistake. Perhaps you origi- nally started with 300PPI, but then had to enlarge the image. Remember, enlarging an image reduces its resolution. If possible, try to start with the maximum amount of pixel information as you can, so you have the flexibility to resize images as needed. Remember, you can always reduce an image's size, but enlarging an image reduces resolution. Avoid resizing raster images in a vector or page layout program like Adobe Illustrator or InDesign. This almost always leads to a resolution mistake. Most raster-based designs are created in RGB color mode. An important aspect of the printing process that needs to be observed is the loss of color range that occurs during the conver- sion of RGB images to CMYK. Generally speaking, the RGB color gamut is larger than a CMYK one. This is where an understand- ing of color management and ICC profiles take the guesswork out of color conversion. This text is reversed out on a built background color. Even the best pressman would have issues trying to line this up. Obviously the text is rendered illegible. You should always design using a properly calibrated and pro- filed monitor. During your calibration process, you should set the white point of your monitor to match the color temperature of the light source from which the final product will be viewed un- der. For example, if your product is to be viewed under daylight conditions, set your monitor's white point to SSOOK. You should also contact your print provider to ask them if they have a press profile that you use to proof colors. You can set up a soft proofing situation, so the colors on screen will represent the way they will look on press. This way, when there are colors lost in the conver- sion to CMYK, it will not be a surprise. If you are accustomed to using spot color inks, or your cli- ent,s logo is created using spot colors, expect the colors to shift in the conversion to CMYK. As mentioned before, the CMYK color gamut does not include all the colors of the rainbow. As a designer, you probably reference your handy Pantone Matching System swatch book regularly to help with making color deci- sions. Unless you are printing spot color inks, this could be mis- leading. One solution would be to get your hands on a Pantone Color Bridge book. This book shows the PMS color and its cor- responding CMYK conversion. This would prevent unforeseen disappointment in the color conversion. GOOD FIRST STEPS Hopefully, these tips will help the next time you are designing a process color label. High-quality print can be predictable and consistent when you know the label's end use, have a good rela- tionship with your printer and prepress vendor and have a good understanding of flexography's capabilities. For a more thor- ough look into the design process, FIRST 4.0 (Flexographic Image Reproduction Specifications and Tolerances) is an excellent resource book for printers and designers. FIRST contains an entire section devoted to the design process (see page 24). The rest of the book will also help give you a better perspective on why things need to be created a certain way for flexography. . ABOUT THE AUTHORS: Gareth Burns is graphic arts program chair at Central Piedmont Community College (CPCC). He has a Master's in Graphicsfrom Clemson University and 14 years experience in the printing industry. Zachery Blackburn is graphic arts instruc- tor at CPCe. He got his Bachelor's in Flexography from Appalachian State University and has 12 years of experience in printing. JUNE 2008 - www.f I exog ra p hy.o rg FLEXO