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FLEXO Magazine : October 2011
The solution when using a consumer camera is to switch out of auto mode and set it to “aperture priority mode” or “manual mode” in order to use the smallest aperture for the available light. The best solution, however, is to use a tilt/ shift lens or a view camera that allows for tilting the area of sharp focus along the plane of the subject. The key to getting everything in focus is using enough light, smaller apertures and camera movements to control depth of field. Shots with a blurry background that fades to nothing should generally be avoided in flexographic printing. Factor: Digital Blurriness Digital photos require sharpening because the nature of digital imaging is, frankly, blurry. These images appear blurry because of the way that pixels manifest themselves when the edges of subjects cut across pixels. The white background is recorded as white and the black image is recorded as black. Individual pixels cannot record the object’s edges as half black and half white, so they record gray tones that soften the edges of the object. solution: sharpening Sharpening is needed to fix digital blurriness and to make the edges appear sharp again. Sharpening filters make dark edges darker and light edges lighter by increasing contrast along the edges of objects. It is either done automatically as a part of the camera’s programming, or after taking the shot in an image-editing program. Sharpening in post-processing is preferred. The best results are obtained when sharpened by a color specialist who understands what happens to images when they are printed.Control is necessary to determine how much sharpen- ing is enough, which programs to use, what size to view the photo when sharpening and how large to make the sharpen- ing lines. If the shot is in focus and there is enough detail, texture and resolution, the sharpening filter has something to grab onto and can make the photo look razor sharp. Most Prosumer cameras have built-in sharpening features that can be controlled, so these settings should be turned off so that photos are not sharpened twice. every little Bit helps... or can hurt Scaling, setting color neutrals, setting white-points and black-points, and CMYK conversion are factors that can affect the quality of photos for flexography and must be con- sidered. Enlarging a photo excessively will soften the image and reduce contrast. Per FIRST (Flexographic Image Reproduction Specifications and Tolerances) guidelines at 100 percent enlargement, 300 dpi resolution is necessary for 133 lpi or 150 lpi line screen. Scaling is always done before sharpening, and scales over 150 percent should be avoided. If it is unavoidable, scaling in two steps will be preferable to one large scale. A grayscale strip in each shot is necessary to determine a color neutral reference, a white-point and a black-point. FIRST specifies that highlight settings should be between 236 and 240, and shadow settings should fall between 18 and 22. Digital files should remain in RGB, so the prepress house tilting the plane oF sharp Focus solution: 68 FlEXo october 2011 www.flexography.org