Buying guide: Scanners

Introduction:

Computer scanners connect to most computers through a USB port or a Parallel port; these connectivity ports act as the medium for transferring data between the scanner and the computer. Mentioned as under are the main types of scanners:

1. Flatbed scanners: The most widely available and commonly preferred scanners are also known as desktop scanners. A glass surface covers over it, on which the paper sheet to be scanned is placed face down. The scanning begins after the cover or lid is closed down on the paper placed upon the glass surface. A detailed narration of this process is given later in this guide. Flatbed scanners provide scanning of A4- as well as Legal- size documents. 

1. Handheld scanners: Based on a similar mechanism as flatbed scanners, handheld scanners are document scanners and are not as large and cannot scan large documents, because their scanning heads measure about 4-5 inches in width. An example of a handheld scanner is the one used at payment checkout counters of departmental stores that read bar codes and the relevant details stored on a computer.

1. Sheet-feed scanners: In a sheet-feed scanner, unlike the system seen in flatbed scanners, the paper sheet is actually transferred over and across its scanning head, which remains stationary without actually moving at all. These scanners are quite smaller compared to flatbed scanners.

1. Slide scanners: This scanner, also known as a negative or transparency scanner creates positive images from negatives, slides, or transparencies after scanning is completed.

1. Drum scanner: Drum scanners are mostly used in the printing or publishing industry. They function using a photomultiplier tube (PMT). Any paper sheet for scanning is rolled around a glass cylinder that has a photo sensor at its center for separating light reflected from the document into three distinct light color beams. After passing through a color filter, each beam is then transformed into an electrical signal inside the PMT.

You will also come across police scanners and radio scanners while shopping for scanners online. Not to confuse with the usual document scanners, these are nothing but tracking scanners mostly employed for traffic management on roads, and highways. Such scanners including digital police scanners are now also available commercially and offer a lot more than the usual tracking functionality. Bearcat scanners and Uniden scanners are some prominent police radio scanners.

Benefits of a scanner

In today’s computerized world, every organization aims at lessening the burden of decades of piled up files and rooms filled with heaps of paper documents by having truly paperless office. This serves as a dual benefit of freeing up a lot of space at the office, and also reducing the hazardous risks of important documents being exposed to natural elements, or even facing destruction in the event of a fire. This versatile machine has eliminated such dangers as now every document in the office can be scanned, and saved into a computer permanently.

The scanner, even used at home for personal items, is now an indispensable peripheral device along with the humble home use printer. People share personal or family photographs taken on older analog (non-digital) cameras with friends and relatives using the Internet. Though, using conventional method to send your loved ones a copy of the photograph required using the negative for developing and printing another copy of the photo that would be then mailed. Today, photo scanners simplify the process by allowing one to scan and save such older photos into an electronic image file on the computer, which can be then emailed via the Internet or uploaded on networking sites.

A transparency adaptor (XPA) provides scanning even negative images for producing a positive output of the original image on the computer. Another attachment accessory, the Automatic Document Feeder (ADF) and the Automatic Photo feeder (ADF) facilitate scanning several individual documents or photos continuously without requiring any user intervention.

How does a scanner work? 

To understand how scanners work, let us first consider a flatbed scanner, as this type is the most widely used across the world. Its basic principle, and the underlying technology implemented in this scanner, is pretty much similar in all other types of scanners.

A flatbed scanner comprises a transparent glass that forms its upper surface of its main housing. This spotless, non-refractive glass is usually covered by a hinged lid, which has a white plastic sheet or thin foam attached to its undersurface. After placing the document face down on the glass for scanning, the lid is then lowered to apply minimal pressure and remove any air trapped underneath the paper sheet. The clear white surface of this cover allows the scanner’s sensor mechanism in identifying all of the color variations on the document to reproduce an accurate electronic image on your computer.

An illuminating lamp passes beneath the glass in specific miniscule increments. This lamp is either a cold cathode fluorescent lamp or a xenon lamp.

The CCD unit, performing the actual electronic capture of the scanned data, is an array of photosensitive diodes that convert light energy into electronic signals. An electro-mechanical assembly comprising precisely angled mirrors, lens, a filter, and the CCD sensor make up the entire scan head. This scanning head moves across the document’s surface from beneath the glass sheet, pulled by a rubber belt that is powered by a unique, small stepper motor. The consequent images of the document exposed to the scan head are reflected by the mirrors onto the lens that successively focus the image through a special filter onto the CCD sensor unit.

Prior to focusing the image on to the CCD sensor, this lens assembly splits up the scanned image into three smaller copies. Each replica that passes through a color filter us separated into a red, green, and blue color image. This color image data falls on a separate section of the CCD sensor unit. The electronic color information from all these three sections of the CCD is then superimposed or merged to form a single, full-color image. Based on the light intensities collected and measured, a differing electric current charge is produced, which results in a replication of the original image.

Purchasing criteria 

Purchasing a scanner is a bit complicated, considering the various technological developments. As under, we have listed a few criteria necessary for consideration before buying a scanner:

1. Resolution: The final quality of the scanned image is based on the scan resolution offered by the device. Resolution is the number of pixels (picture elements) making up the image. Resolution is measured in pixels per inch. Usually, scanners enumerate two resolutions — optical and interpolated. While optical resolution is the deciding factor in the final image quality, interpolated resolution seemingly provides enhancements only during magnifying an image when scanning.

1. Bit-depth: This number of bits per pixel is an indicator of the number of colors stored per pixel. Higher the bit-depth, much superior and vibrant is the final quality of the scanned image. A scanner must provide with a bit depth of at least 24 bit per pixel. Advanced scanners provide as much as 36 bits per pixel, while some high-end professional series provide up to 48 bits per pixel.

1. Speed: High volume scanning requires that the scanning speed is capable of keeping up at a steady pace without reduction in image quality. The speed is directly related with the sensitivity of the CCD sensor unit, and the movement and stability of the stepper motor that pans across and under the scanner’s glass surface.

1. Optical Character Recognition (OCR): This scanner’s function recognizes characters from a scanned text document, and converts these characters to an editable text document for word processing application such as MS Word, Notepad, etc. for later editing. This is a very handy feature for reading and converting from hand written pages or even existing printed ones, and most scanners currently available provide this function.

1. Automatic Document Feeder (ADF): The ADF is a scanner accessory, which enables a stack of A4-sized or Legal-sized documents to be placed simultaneously, where each paper rolls into the scanner’s paper feeding assembly, and is scanned successively, immediately, and automatically.

1. Automatic Photo Feeder: This attachment is much like the ADF, except that it is smaller in size for scanning photos or photo-sized papers, documents, etc. only.

1. Transparency adaptor: This resourceful apparatus uses a unique software application to reproduce the positive image from a negative, slide, or transparency film after scanning.

Making a decision

After thoroughly understanding your needs, and preferences considering the various features mentioned above, you should compare different scanners models available in the market that fulfill your requirements. Some prominent names include HP scanner, Canon scanner, Epson scanner, and Microtek scanner.

A scanner is a very useful machine that combines an innovative technology along with a multipurpose software application for providing an amazing functionality and convenience. When purchasing this equipment, we recommend that you carefully scrutinize the advantages and disadvantages of each scanner model or make available from different manufacturers. You may (and must, actually) also consult with present scanner owners from your peers or friends and family. Ideally, you should check out a scanner unit you intend to purchase for the parameters mentioned above, with the OCR, XPA, and APF, which are must-have facilities.

Most of the scanner manufacturers provide all-inclusive warranties (except for broken glass surfaces due to mishandling while usage). As the internal components of a scanner are quite delicate, and prone to damage if roughly handled, it is sensible to confirm what the warranty covers prior to deciding upon the purchase. Additionally, we recommend you checkout the after-sales service facilities, and online or off-line technical assistance. Rest assured that with correct servicing, any scanner provides quality and performance, and lasts longer.