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FLEXO Magazine : July 2009
DESIGN 4.7 Electronic Whiteout Do not cover up unwanted elements with a white box. The RIP will still process unwanted elements. Files that are designed in drawing programs can use masking, clipping, or compound paths instead. 4.8 Image Capture Quality – Scanning Considerations Optimizing scanner variables when capturing the original image is critical to achieving the desired printed result. Scan Resolution All scanners capture RGB data. Although some scanners can use hardware and/or software to translate the scanned data to CMYK, FIRST recommends capturing and supplying the image in the original RGB format to protect against data loss. Entry-level scanners generally are not adequate for production scans. Such devices use interpolation to achieve production resolution or size, and real detail cannot be interpolated. Image Sharpness/Resolution The most important scanning factor is optical resolution. A scan at 100% scale should have a minimum sampling of 1.5X - 2X over the final halftone line screen. Fine detail images may be sampled at up to 3 times the output line screen. For example, an image that will print with a 200-line screen may need a scan resolution of 300 to 600 pixels per inch, depending on the detail required in the image. If the image is enlarged, it will lower the effective resolution. The objective is to scan images at a high enough resolution to capture enough data to achieve the desired detail at the reproduction size. Image Enlargement DESKTOP SCAN 72 DPI DRUM SCAN 300 DPI 4.8: Scan Resolution: FIRST recommends images remain in RGB format for delivery to prepress. Enlarging a scanned image will reduce the effective resolution of the image, and can compromise the image appearance. If possible, scan the original at the correct size and resolution; if rescanning is not possible, some enlargement may be acceptable depending on the scanned resolution. Adobe Photoshop is able to enlarge images using interpolation – a mathematical process of creating new pixels. Depending on the image, some interpolation may be tolerable. Whenever possible, it is always preferable to rescan the original image at the desired resolution. Line Art Theoretically, line art should be scanned at the same resolution as the output device. However, minimal improvement is visually apparent on most line art subjects scanned above 1,000 pixels per inch. Scaling will degrade quality; the best solution is to redraw line art in an illustration program. This also makes the file size smaller.
Sustainable Spring 2009