Scanners are peripheral devices that convert images on papers, documents, transparencies, and 3D objects to a digital representation. These images can be edited or manipulated at will. Scanning is a process that employs a light source to capture visible texture and colour from documents or physical objects and converts it into digital information. The technology and settings of the scanning device will decide the resulting accuracy and quality. The use of a scanner can be employed both in print and video. There are different types of scanners including handheld scanners, flatbed scanners, drum scanners, photo scanners, and transparency scanners, each one meeting a specific need. Handheld scanners are for budget buyers with little desk space and good for quick scans like card scanning. Flatbed scanners are the most versatile and popular format and are capable of capturing colour pictures, documents, and pages from books and magazines. Although flatbed scanners are not good enough for high quality print jobs, they are becoming increasingly popular among the web community, where uploading and downloading images is an everyday activity. Flatbed scanners that can be connected to a computer are by far the cheapest means of scanning images and producing low-to-medium quality printouts for personal use. Drum scanners scan reflective art and transparencies and have very high resolution and are specifically used in printing and publishing houses where high colour photographs are to be reproduced with or without image manipulation. These kind of scanners are very expensive and will not prove useful for someone who just wants to scan favourite family snapshots or works with images that need to be incorporated into the design of a website. An average user or web enthusiast is better off investing money wisely in a feature rich flatbed scanner, that is compatible with most computer systems. Photo scanners work by moving a photo over a stationary light source and are compact. Transparency scanners scan negatives that pass light through an image rather than reflecting light off it. Most desktop scanners resemble each other in basic rectangular shape and assembly. A conventional desktop scanner consists of a hinged cover, a glass sheet, a carriage assembly, a power slot, interface slots, and buttons. A hinged cover is used over the document or the object to be scanned. A special glass sheet is used to place the document or the object to be scanned. A carriage assembly normally contains a motor, a lamp, a mirror, and an image sensor. A motor moves the light source while performing a scan. A lamp is a device capable of projecting a beam of white light that spans across the breadth of the scanning area. A key feature missed out by many scanner manufacturers are lamps and lenses used in most cheap and high-end scanners. The right lens contributes a lot to the overall image result. Scanners use one of several lamp types that include cold cathode fluorescent lamp, xenon gas cold cathode lamp and ‘Light Emulated Device’ (LED). While the fluorescent lamp generates little heat and prevents image distortion, xenon gas cold cathode lamps brighten up faster and last longer, but are expensive to integrate. Xenon lamps produce a stable full-spectrum light source that is both long lasting and quick to initiate. Xenon light sources consume power at a higher rate than cold cathode tubes. The most commonly used lamp is LED, as it uses little power that makes it possible for a scanner to be powered by a ‘Universal Serial Bus’ (USB) or a fire-wire connection. It is cheaper, compact, and has a greater lifespan compared to the other two options. But it does not provide the same level of richness in colour or detail. Cheaper scanners use a fixed focus lens wherein the focus of the lens is set to what is just beyond the surface of the glass. This is fine if a flat image is being scanned. But the same may not be true in the case wherein a book is placed which may not be flat. Fixed focus scanners will not be able to produce what is near the spine of the book. The more advanced scanners use focus control, where the focus of the lens changes depending on the distance of the document from the glass and the mirror. This not only helps when scanning 3D objects, but also provides better control over scans of slides or chromes in slide holders, since these are placed slightly farther away from the lens than other objects. Cheaper scanners use plastic lenses, while professional quality scanners use glass lenses. A mirror reflects back an intensity of light to an image sensor. An image sensor consists light-sensitive photocells. The light beam that is emitted from the movable assembly hits the surface of the document and reflects back an intensity of light depending on light and dark areas from the document. The reflected light passes through certain photo cells, which categorizes the information into values, based on the intensity of light detected. The entire information is then sent to the software application that organizes the bits and bytes of information, presenting it as a digital image on the monitor. This image will incorporate changes like brightness, contrast, and colour that were preset when the scan was performed. An image sensor is either a ‘Charged Couple Device’ (CCD) or a ‘Contact Image Sensor’ (CIS). CCD sensors are precise and accurate, and are widely used and recognized by industrial standards as the best in digital imaging. CIS on the other hand, is smaller and more compact than a CCD sensor, but the results are noisy and are generally not recommended and therefore less popular. CIS scanners employ dense stock of ‘Red Green Blue’ (RGB) LED to produce white light and replace the mirrors and lenses of a CCD scanner with a single row of sensors placed extremely close to the source image. The CCD and CIS digitise the results through an ‘Analogue to Digital Converter’ (ADC) and sends the resulting information to the scanner’s hardware and from there to the computer system. Single-pass scanners work quite differently when compared to multi-pass scanners. In single-pass scanners, there are two different methods that are followed here. The first method involves an extremely fast rotating light filter that individually filters the RGB components of the reflected light and is sensed by a single CCD device. Here the colour filter is fabricated directly into the chip itself. Another method that is adopted is a prismatic beam splitter that splits the reflected white light and the three individual CCD sense the RGB light. This method requires a high precision in the alignment of the sensing mechanism and optics. A power slot is used to connect a power cable. Interface slots are used to establish communication between a scanner and a computer via an interface cable, e.g. Parallel, ‘Small Computer System Interface’ (SCSI), ‘Universal Serial Bus’ (USB), etc. Today, much of the scanners available are dual interface with either SCSI or USB with parallel interface. SCSI is an expensive solution with an additional cost of SCSI card involved. USB is a cheaper solution and it has been widely accepted. The presence of USB interface on almost all new motherboards has helped ease the pain of installing the scanner. This has also increased scanning speed due to the higher data transfer rates it supports. Today, scanners come with the hi-speed USB 2.0 interface that has 480 MBPS speed to help transfer data faster. Some buttons have optional preset functions that perform one touch scanning tasks. Integration of one-touch buttons like scan, copy, mail helps the cause of scanners further. Some scanners have the in-built functionality that scans transparencies directly so no need to go to a photo studio to scan negatives. When the scanner is switched on first, it under goes a warm-up, which basically means readying the scanner for use with the attached computer. The actual process of scanning can either be triggered by pressing one of a set of buttons on the scanning device itself or through a menu item inside a software application that can recognize a scanning device and its associated driver. Once the scanning function is activated, necessary instruction of the scanner that forces the carriage assembly to move in a particular direction from one end to another of the document or the area defined by the preview rectangle marquee from the launching software or scanner application placed facedown on the object glass. Scanners come with different specifications and features like maximum optical resolution, colour depth, paper size accommodations, and optional transparency adapters. The resolution of a scanner is measured in ‘Dots Per Inch’ (DPI). It is also interchangeably known as ‘Pixels Per Inch’ (PPI). This is a fixed number based on the number of cells in the array and the total area scanned. The smaller the area, the better the resolution. Higher DPI has the more clearly scanned image. Each image is made up a collection of small tiny dots or pixels. So an image with a resolution of 300 DPI would mean each inch area of the image is made up of a grid of 300 dots. Resolution is also divided into two categories, optical and maximum. The optical resolution is true scan resolution that justifies the resulting image, while the maximum resolution is interpolated. This means that with the help of software adjustment and ‘Technology Without An Interesting Name’ (TWAIN) drivers, the image is blown up to a higher DPI. TWAIN is a cross-platform interface that was developed by professionals from companies like ALDUS, KODAK, and LOGITECH for acquiring images captured by scanners. Software interpolation can increase the resolution more than hardware interpolation by packing in more bits of colour information that matches the surrounding colour pixels so that a picture does not appear blurred when expanded. Interpolated images will always look very smooth, but slightly out of focus and are not accurate. Interpolation has the effect of smoothing out jagged edges. But for continuous tone images like photographs, it is better to stick with the actual optical resolution. Many scanners can produce lower resolutions with the proper software. Some offer increased resolution on one axis by taking readings more often as the light bar moves. Interpolation is another method of improving resolution mathematically. An algorithm is used to calculate the value of a pixel from the two images that are actually scanned. If one of the pair read as 8 and the other as 12, the algorithm would place the value between the pair as 10. The success of the final image depends on the type of material being scanned. The colour depth is yet another term that signifies the number of bits per pixel. When a scanner converts something into digital form, it looks at the image pixel by pixel and records what it sees. This part of the process is simple enough, but different scanners record different amounts of information about each pixel. How much information a given scanner records, is measured by its bit depth. The simplest kind of scanner only records black and white, and is sometimes known as 1-bit scanner because each bit can only express two values, on and off. In order to see the many tones in between black and white, a scanner needs to be at least 4-bit for up to 16 tones or 8-bit for up to 256 tones. The higher the scanner’s bit depth, the more accurately it can describe what it sees when it looks at a given pixel. This, in turn, makes for a higher quality scan. The alternative route to improved quality to provide cleaner data, which is less affected by random noise in the lower order bits, is actually expensive. This approach would require highly precise optics for focusing reflected light to the CCD that captures the data, minimal distortion glass free from internal contaminants, CCD that captures light and converts it to electrical signals with high accuracy and a smoothly moving scanning head with little vibration. Such a device would cost considerably more than one that used lower-cost and lower-quality components with slightly more expensive ‘Analogue to Digital Converter’ (ADC), capable of capturing 10-bit and 12-bit of data each for the red, green, and blue colour components respectively rather than just the average 8-bit of data. Since CCD captures brightness levels, it makes sense that they can be found in greyscale scanners, which are used for reproducing both continuous tone and line art originals. A scanner captures colour with the same CCD by creating three separate versions of the image, one for each of the three primary colours of light reflected by the target. Most colour scanners do this in three passes. One pass with a red filter records the red filter records the red components, a second pass with a green filter records the green light, and a final pass with a blue filter records the blue. True colour scanners record 8-bit of data for each pass, for a total of 24-bit of data per pixel. The result is a composite image with 16.7 million possible colours of 24-bit colour. A 24-bit image comprises three 8-bit colour channels ‘Red Green Blue’ (RGB) containing 256 colours, producing 16.7 million colours when combined. The 24-bit colour is also known as true colour and photo-realistic colour. A 32-bit colour images has four colour channels, RGB and 8-bit of grey scale data to provide higher detail. Lightweight, compact, feature-rich with high-performance components integrated into a scanner are the spots manufacturers are working towards. The scanner, which used to a luxury not so long ago, is now well within the reach of most people. The prices have fallen both due to the competition between numerous manufacturers and the advancement of the technology used. This has put it high on the shopping lists for many home users, who basically use them to fun, explore, and maybe even compile their photo albums online.

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