Understanding the concept of resolution is imperative when acquiring a usable scan. When setting up the scanner, you will need to know the size that the image will be used, and the minimum resolution (depending on a particular printer or other output device) necessary to maintain quality.
The largest dimensions that the image will occupy must be considered before determining scanning parameters. You can subsequently make a scanned image smaller, but you can never magnify it without a loss of resolution and quality. If you are unsure of how large the image will be used, it is better to ere on the side of being too large.
Use the Image Capture application with the scanners in 136 and 142. Different manufacturers produce their own software, which may differ in appearance, but share common settings, such as:
• source type (black & white or color negative, transparency or reflective art)
Flatbed scanners are best suited for reflective art, such as photographic prints or images from books, and usually accommodate originals up to 8.5″ x 11″. Some flatbeds have provisions for transparencies (which includes a light source built into the lid, shining down through the transparency,) but dedicated film scanners usually do a much better job with transparent media.
You can use flatbeds for paintings or even three dimensional objects, but special care must be taken to protect the glass surface of the scanner. Never place anything on the glass that will cause a scratch or leave residue behind. Use a clear acetate to protect the glass if necessary, and never close the lid on any object other than a flat print or small book.
Once your object is placed on the glass, a Preview is done to reveal the entire scanning area. Drag a selection marquee around the image area you wish to scan, and do a Prescan to allow the scanner to calibrate itself based on your desired scanning area. Then a final Scan can be completed.
• resolution (measured in pixels per inch (ppi))
Determine the resolution necessary for your ultimate output device. For color printers, a minimum of 150 ppi is necessary. For higher resolution printers or imagesetters (for offset press output) 300 ppi or more may be necessary. For Web or other screen-based art, 72 ppi is adequate.
• original size
Once you’ve done a Prescan, the software will tell you the actual size of the image area you have selected.
• scaled percentage (magnification)
Determine the largest size you wish to use this image area. You can increase (or decrease) the magnification setting to make the resulting scan larger or smaller than the original to match your intended use. The Output size = the original size x scale percentage.
Note: You can leave the magnification at 100%, and instead increase or decrease the resolution to achieve a larger or smaller file size. For example, scanning at 300 ppi at 100% will result in the same file size as 150 ppi at 200%.
• color and tonal correction
It’s possible to adjust the scanner settings to compensate for over/underexposed or poorly color corrected originals. However, it’s preferable to allow the scanner to scan at automatic default settings, and then correct the scan with Photoshop.
All scanners blur when acquiring data. Sharpening filtration is available to compensate for this. Normally, the “Auto Sharpen” filter setting is adequate.
When scanning an image with a halftone screen, that is, one that was printed on an offset press or laser printer, an unsightly moiré refraction pattern can result. Moiré appears when two dot screens overlap, and, as the scanner introduces another screen on top of the original screen, this phenomenon is common. Most newer scanners include a descreening filter to reduce this. Choose a setting corresponding to the line screen of the original source — newspapers have course screens (around 65 lines per inch (lpi)) low quality magazines are usually 133 lpi, and higher quality magazines can be 150 or 175 lpi.