A: Optical Resolution
--- Optical resolution is limited by the number of sensors built in CCD. Take a
600-dpi-optical-resolution scanner of which scanning width is 8.5 inches as an example. In
order to sample 600 dots per inch, there must be at least 5,100 usable charge couplers in
CCD. While for 300 dpi scanner, the minimum sensors needed in CCD is 2,550.
Mechanical Resolution --- During the whole scanning process, the
CCD captures the draft image data line by line, while the scanning module
mechanically moves step by step. The horizontal (x-direction) resolution is limited by
CCD. On the other hand, the distance that the scanning module moves during the exposure
determines the vertical(y-direction) resolution. So a 1/600-inch movement each step is
equal to an 600-dpi vertical sampling rate, therefore, the mechanical resolution is 600
dpi.
Maximum Resolution (Interpolated Resolution) --- Most scanner manufacturers have developed
methods to increase resolution by software or hardware interpolation. This
higher-than-optical resolution is achieved through some different algorithms of
interpolation. The most common one is to average the number of adjacent sampling pixels to
increase total pixels in the given sample, thereby resolution boosts as the vendor wish.
The other algorithm used is replication to increase the number of pixels. These two
techniques are often combined to boost resolution from true optical one to four times
interpolated resolution or even higher.
A: TWAIN was developed by a consortium of software and hardware companies including Aldus, Caere, Eastman Kodak, Hewlett-Packard and Logitech. It is an interface standard of application software which ensures the compatibility of scanner hardware with application software such as OCR and image editing programs. This standard enables users to scan images directly into application software without exiting from the application.
A: The number of bits of the analog-to-digital converter determines the scanner's gray levels and color depth. Color depth is an important specification affecting the color ability and image quality of scanners. For example, a color scanner of which color depth is 24-bit(8-bit for R, G, B each) can provide 16.7 million different colors. A 36-bit color scanner can offer 1 billion colors.