Chapter 4 Problem Solving and Service Information.

Terminology

Q: What are the difference among Optical resolution, Mechanical and Maximum resolution?

Q: What does TWAINstand for?

Q: What is Color depth?

Q: What are the difference among Optical resolution, Mechanical and Maximum resolution?

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 image data of the draft 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 of 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 and 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 number of adjacent sampling pixels so as to increase total pixels in that 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.

Q: What does TWAINstand for?

A: TWAIN was developed by a consortium of software and hardware companies that include Aldus, Caere, Eastman Kodak, Hewlett-Packard and Logitech. It is an interface standard of application software which is developed to ensure compatibility between scanner hardware and application software such as OCR and image editing programs. This standard enables users to scan images directly into application software without exiting the application.

Q: What is Color depth?

A: The number of bits of the analog-to-digital converter which determines the scanner's number of gray levels is color depth. Color depth is an important specification affects 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. For 30-bit color scanner, the number of colors offered is 1 billion.