Scanner is a peripherals attached to a computer, but external to the main case that houses the CPU, Hard drives, and internal components. These devices allow smooth interactions between the computer and its users.
Scanners convert captured images and text into computer-readable forms for ease of access to users. The scanner uses a light source that reflects off the image being captured. This information about the reflected image digitized and sent to software for storage, editing, or printing.
A scanner, whether handheld or flatbed, uses one of three methods to capture and reproduce the image of the document it scans.
IMAGING METHODS OF THE SCANNER
Photo-multiplier Tube (PMT):
This type of scanner uses a vacuüm tube to convert light reflected from the scanned image to an amplified electrical signal sent to the PC. Photo-multiplier Tube scanners are more expensive and generally more difficult to use than Charge-coupled device scanners (discussed next). High-end applications make use of this.
Charge-Coupled Device (CCD):
This class of scanner includes the general-purpose scanners used in homes and offices. A Charge-coupled device is a small solid-state sensor that converts light into an electric charge. This is later converted into digital data stored on a PC. This type of scanner uses literally thousands of CCDs in an array that scans the entire surface of the image. More Charge-coupled devices in the array translates into a higher maximum resolution for scanned images.
Multi-pass and Single Pass Scanner:
Multi-pass scanners collect color data using multiple passes of the light source and CCDs array over the surface of the image. This is necessary as single scan gives the red, green, and blue information on the page. At the end of the three passes, the collected color information combines to make a full color image. The drawbacks of this method are:
- it takes time make three passes, and
- the image quality can suffer from tiny inaccuracies due to alignments of the three sets of data combined to create the composite image.
A single-pass scanner collects all the color data in one pass. The result is usually a faster scan with less potential for image distortion than a multi-pass scan.
Scanners, like most external peripheral devices, attach to the PC through one of its available ports. The most commonly used connector is the parallel port, but several newer versions are now available with a USB interface as well. Higher-end scanners connect to the PC through the SCSI interface.