The biggest key to success is to have a fast scanner. Even though a dragonfly may be drowsy from cold and seemingly quiescent under a scanner cover, it will warm quickly. If a wing flickers or the legs move, a discontinuity will result in the scan, although small movements will be nearly unnoticeable. The scanner used for these images was a Hewlett-Packard Scanjet 4c, a single pass scanner capable of 600 dpi (dots per inch) resolution. An image can be obtained in as little as 20 seconds. Some scanners require multiple passes and can take two or three minutes to acquire an image. This model will work with both PC and MacIntosh computers.
The computer attached to our scanner is a generic Pentium-100 PC with 16 MB of RAM and a 1.6 GB hard disk. The type of computer is less important to the scan than it is to the post-scan manipulation of the file, although most scanning software for PC’s requires the WindowsTM interface. This mandates an Intel 386 processor or its equivalent as a practical minimum.
For high quality on-screen viewing, the monitor and card must be capable of displaying in a resolution of 640X480, although higher resolutions (800×600 or 1024×760) allow more work area on the screen and a potentially better view in that the whole image may fit on the screen at once. Higher resolutions require more memory if accurate colors are to be displayed, and the on-board memory of many VESA and PCI video cards can be expanded. These cards normally come with one or two MB of video RAM, but to display the image at higher resolutions in RGB color (24 bit), more memory – up to eight megabytes – is needed. The number of colors displayed by a monitor and card is a function of 2 raised to the power of the bit depth. A 256 color card is 8 bit color or 28. High color is 16 bit (216) or 65,536 colors. RGB color imaging is at 24 bits or more than 16 million colors, while 30 or 32 bits displays in excess of 1 billion colors and is considered true color. However, a computer and monitor capable of displaying 24 bit color cannot do so unless the scan was made in 24 bit color as well. An 8 bit scan, for instance, will only display in 8 bits. The quality of the image for both viewing and printing is based on the number of colors displayed, the resolution at which they are displayed, the resolution of the scan in dots per inch, and the color depth of the scan. These scans were done at 300 dpi in 24 bit color and are displayed on a 17″ monitor at 1280×1024 resolution in 24 bit color. The result is an image of photographic quality. As a practical minimum for sharp viewing, the user should strive for at least 800×600 resolution in 16 bit color on a 15 inch monitor.
Once a scan is obtained, it may be saved to a hard disk and then further manipulated. Even relatively small scans in RGB color can make for a large file — two to three megabytes are common. However, the files may be compressed and reduced to fit on a single 3.5″ floppy disk. For example, a 3386.5 kilobyte BMP (bit mapped image) file can be reduced to a 466.7 kilobyte file by converting it to JPEG (Joint Photographic Experts Group) format, an option found in many image viewers. This type of compression may involve some data loss however, and while it may not be visible to the eye, image analysis would be able to discriminate between the two. If the image is only for viewing or downloading, then the JPEG format is the format of choice. If all the data in the image are needed, then a BMP or TIFF (tagged image file format) type file would be a better choice. GIF (graphics image format) files are unacceptable as they are limited to only 256 colors. Large hard disks and high capacity removable disk drives (ZipTM and JazTM drives) provide affordable storage and rapid file access. Tape cartridges are less expensive for mass storage, but files are difficult to access since the tape must be wound back and forth to find the beginning of each file.
Inexpensive inkjet printers can provide near-photo quality output of these images. Many are available that can print 600 to 720 dpi in full color. For higher resolution, coated paper is a necessity. This paper prevents ink from bleeding off the area where the ink nozzle has applied it. Lower resolution images (180 to 360 dpi) may be test printed on plain paper before the final output is produced.