Computer Info – November 10, 1999
This Week’s Program --- Scanning         We hope to discuss and demonstrate using a scanner this week. Scanners         There are typically two kinds of scanners – flatbed scanners and sheet-fed scanners. Flatbed scanners look and function like a miniature copy machine. You can place the material you want to be scanned (whether it is papers, photographs, books or even small objects) in the scanner. The scanner has a moving light and sensor device that essentially analyzes and then digitizes an image of the object placed on the glass.
        Sheet-fed scanners operate more like printers, but in reverse. You feed a document into them one page at a time (which makes them unsuitable for anything but individual pages) and the scan head inside them scans the page as rollers pull it through. One example of a sheet-fed scanner would be the combination printer-fax-scanner.
        The critical features to look at when comparing scanners are:
                    1. The optical resolution and color bit depth
                    2. The interface it uses to connect to the PC
                    3. The software bundled with the scanner. Resolution: Optical Versus Interpolated         The most important specification to look for in terms of comparing scanner quality is the resolution. The scanner’s resolution determines the degree of detail that it’s capable of working with.
        Scanner resolutions, which are quoted in dots per inch, refer to how many pieces an image is broken down into in order to convert it into digital format. The higher the resolution, the smaller the pieces, and the smaller the pieces, the better the quality. You will notice that scanner manufacturers list two different resolutions: the optical resolution and the enhanced or maximum resolution. The optical resolution is the real resolution of the scanner – it reflects what the scan head is actually capable of doing. Enhanced resolutions stem from the fact that most scanners also have the capability to enhance this optical resolution by essentially adding in extra pixels in between the pixels the scan head actually generates (a process referred to as interpolation). In theory, this sounds good – in reality, it rarely works well and causes more problems than it’s worth. So, for most applications, it’s pretty much worthless. In other words, ignore a scanner’s enhanced resolution spec, and look only for its optical resolution. Color Depth         Color depth is measured in bits. The higher the number, the more colors the scanner is capable of capturing. The default setting for most scanners is 24-bit color (or 16.7 million colors). Interface Type         Scanners connect to your PC either through a SCSI (Small Computer Systems Interface), a parallel connection or a USB port. Scanners create and need to transfer a lot of data, so the higher performance SCSI and USB connections will enable a scanner and your PC to work more efficiently. Bundled Software         Virtually all scanners come bundled with a variety of different software packages. Most include some kind of image editing program for scanning in and editing photographs and an optical character recognition (OCR) program, which can convert the digital image created by a scanner into editable text. The quality of the image editing and OCR programs that comes with different scanners can vary tremendously. Not surprisingly, lower-cost scanners tend to come with less powerful programs (or cut-down versions of more powerful programs) and higher-priced scanners tend to come with more full-featured programs, such as Adobe PhotoShop. Determining What Resolution To Use         You should always base your scanning resolution on the output device you intend to use. If you plane to just view the images on screen, such as for a Web site, use a resolution setting that’s typically pretty low (100 dpi) and if you plan to print them, use a higher resolution (200 to 300 dpi). You make these settings in your scanning software, which typically works in conjunction with your image editing program. Often times you will see a option such as Image Acquire from your program’s File menu. When you do this, you will be accessing your scanners interface through the TWAIN or TWAIN32 software interface.       Resolution and Image Size         The higher the resolution of a scanned image, the more dots it has, and the more dots it has, the more space it takes up. Here is the formula:
        File size (in bytes) = height of photo (in inches) times scanning resolution (in pixels per inch) times width of photo (in inches) times scanning resolution (in pixels per inch) times 3 (for 24-bit color, which is made up of three 8-bit bytes). So, for example, a 4 x 6 photograph scanned at 100 dpi with 24-bit color is: 4 x 100 x 6 x 100 x 3 = 720,000 bytes or 703 Kbytes. One potentially confusing point is that 30-bit and 36-bit scans take up twice as much space as 24-bit scans because each color (red, green and blue) requires two bytes to describe the data captured in a 30 (or 36-bit) scan, versus one byte each in a 24-bit scan. Can Your Program Handle 30 or 36-bit Resolution?         If you have access to a 30 or 36-bit scanner, one common question is whether or not to use these higher "bit" resolutions when you scan. In theory, they should provide an even higher-resolution image than a normal 24-bit scanner, but the reality is that on most photos, these settings make little difference. Photos with a lot of details in shadow can often benefit from these higher resolutions, but not all image-editing programs can even work with images at higher than 24-bit resolution. Even Adobe’s high-end PhotoShop image-editing program can’t edit images with more than 24-bits. In some situations, in fact, the extra bits are simply "tossed out" by the image-editing programs. Clean Personal Files From Hard Drive Before Selling Your PC         To make sure that the programs, files and data from your system are not recovered by the next person to own your computer, try this.
        First uninstall any programs that you do not wish to give away with your computer. Delete any of your personal documents. Now create a new folder called Wipe (or some name you’ll remember). Next, load a CD-ROM or diskette into your machine (pick something harmless such as a CD-ROM dictionary or your Windows installation CD). Start copying files from it to the Wipe directory.
        Continue copying files until you actually fill your hard drive to capacity (if you have a large hard drive, this could take some time). When the drive reaches a point where you literally cannot copy any more files to it, you will have overwritten all your previously saved data, making it impossible to retrieve. Now delete the entire Wipe directory and empty the Recycle Bin. Your deleted information is now very, very gone. Web Addresses Search phone directories in many countries
                 http://www.phonenumbers.net
European search engine
                 http://www.euroseek.net
Tutorial for Netscape 4.5 e-mail
                 http://home.netscape.com/browsers/using/newusers/messenger/
Telephone directories from around the world
                 http://www.teldir.com/eng/
The Internet Public Library
                 http://www.ipl.org/