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The Basics of Scanning

Resolution…What’s That?
In a simplified nutshell, resolution refers to the quality of a scanned image or photograph. There are two different types of resolution: printer resolution (dpi or dots per inch) and monitor resolution (ppi or pixels per inch). The term dpi refers to the dots printed per inch on a piece of paper. The term ppi refers to the number of pixels per inch that compose an image on screen. For web images you need only be concerned with ppi, but both types of resolution affect your final printed document. Basically speaking, the greater the dpi of your printer, the better the print quality. The greater the ppi of your image, the sharper your printed image will be, to a certain extent.

File Sizes of Scanned Images
A 4" x 6" color photo scanned at 300 ppi creates a whopping 6 MB file. This resolution is about what you need for commercial printing, but is probably overkill for your office printer. If you scanned the same photo at 600 ppi (you would never need this high a resolution), this image is nearly 24 MB! The same photo scanned in grayscale at 600 ppi would be only 7 MB.

With this in mind, choose the lowest possible scanning resolution (ppi) that will still creates good-looking output on your printer. If you scan at too high a resolution you create a HUGE file that doesn't print any better than a smaller file. If you are printing in black and white, select black and white or grayscale for your scan rather than color.

Final Print/Web Sizes of Scanned Images
The resolution is linked to the visual size of the image. If you increase the dimensions of the printed image, the resolution will decrease and your image will not look as sharp. If you reduce the printed size of the image, your file will not look any better, but will be unnecessarily large.

So try to scan photos or graphics at the actual size of your final image; use the scanning software to enlarge the image if necessary. If you’re not sure of the final size, scan larger, then reduce the size later in an image editing program (like PhotoShop). You can always reduce the size of an image, but you can't enlarge it; there is not enough information in the file to tell the image what to look like. Don't "drag" a scanned image in a program like Word to resize it. Enlarging it this way will reduce the quality. Shrinking it will create a much larger file than what you actually need.

Line Art vs. Photos
For line art with no shading (such as a logo) you should usually match your printer’s dpi resolution (600 -1200 for most laser printers). For other images or photos, it is seldom necessary to scan at the same resolution as your printer; consult your scanner or printer manual. Or try scanning at several different resolutions, then print each scan to determine the best trade-off point (smallest file vs. best image).

Scan Settings
The automatic settings (exposure, contrast, etc.) for most scanners work well in many cases, unless you need to correct a poor-quality photo. When you experiment with the settings, be sure to examine the effect of the printed image, since the scan preview often looks a lot different than what actually comes out of the printer.