by Bob Brooke
Family genealogists are rapidly adding scanners to their home computers as prices drop and performance improves. Since sharing and caring for the past are your two most important tasks as a genealogist, your scanner may be your most important tool. However, most people don't know how to scan photographs correctly.
A scanner lets you input any kind of image into you computer, but it can quickly eat up your system's memory and hard disk space. Because today's scanners offer higher resolutions and more colors than ever before, they're capable of producing huge files that quickly gobble up disk space.
When you scan an old photo, you create an image file. The amount of space the file takes up on your hard disk is directly related to both the size and complexity of the photo and the resolution used when you scan it. Resolution is measured in dots per square inch (dpi). For example, doubling both the horizontal and vertical resolution going from 300 by 300 dpi to 600 by 600 dpi quadruples the size of the image file. A 6" x 4" photo print scanned at 600dpi produces a 25 megabyte image! Also, the higher the resolution, the longer it takes to scan the photo. The old saying, "A picture is worth 1,000 words," is more than true with scanned images.
Scan resolution merely determines image size. When you increase scan resolution, you increase image size. A 6x4-inch photo scanned at 110 dpi fills about half of a 1024x768 monitor screen, the typical resolution of most computer monitors today.
Images in newspapers and magazines are reproduced quite differently from photographic prints. They're reduced to a series of small dots. When scanning these, you can easily get an interference pattern between the dots on the original and the dots scanned. Some scanners allow you to "descreen" when scanning--blurring the dot pattern so it appears more like a photograph. This process is very effective and is better than trying to overcome the screen or patterning in your photo enhancement software after you scan your image. Scanning at high resolution is another way to eliminate these patterns. To scan old engravings, set your scanner to Line Art at 600 dpi.
Large images also consume memory. An image's memory is computed from its size. A fairly ordinary picture can take up 1.5 megabytes of hard disk space which is equivalent to about 180,000 words–an ordinary novel.
You must learn to vary your scanning depending on the nature of the picture. If a subject is important, devote the needed space. On the other hand, you can save lots of file space by scanning only that portion of the image needed and/or saving as a smaller size. When the scan resolution is doubled, memory size increases four times. Many people scan black and white photos as color, thus increasing file size three fold. And there's no advantage in saving monochrome images as color.
To reduce file size, reduce resolution. So by reducing your resolution to 72 dpi after you scan, you save four times the memory–ideal for publishing an image to a Web site–but retain the detail you need in the photo. You can do this easily by changing your image's resolution in either the Edit or Image menus of manipulation software such as Ulead PhotoImpact or Adobe PhotoShop.
File size can also be reduced if you save images in a compressed file format. All images can be saved as .jpg or JPEG (pronounced JAY-Peg) which take up a fraction of the original file size. When you open up a JPEG image, it's automatically decompressed and displayed as normal. However, you can't scan an image as a JPEG. Your scanned image will almost always be a .tif or TIFF (Tagged File Format) file. Instead of just naming the image before you save, go to Save As, scroll down to JPEG and then Save.
In the next column, you'll learn more about saving and restoring your old photographic images using image manipulation software.