CIRCA:Scanning
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Scanning Technology
This brief paper discusses the basics of scanning technology, its history and development, related technologies, significance, and its place in the future.
Introduction/Background
The process of converting data into computer format is by digitizing them, and the way in which graphics are digitized is by scanning. According to Online Technology Learning Centre (2002), scanning “is the process of transforming a physical media into a digital file and then formatting that file so that it can be read by a computer application.” The physical media can be items such as a photograph, small objects, text, or even a document in the form of paper etc. It can therefore be deduced that scanning is also the process of converting files, images, and data into easily accessible, retrievable, and searchable electronic formats. WordNet defined scanning “the process of translating photographs into a digital form that can be recognized by a computer,” or “as the act of systematically moving a finely focused beam of light or electrons over a surface in order to produce an image of it for analysis or transmission.” As a means of converting data into a computer format, scanning of documents and images is usually carried out using a scanner. Scanner, often referred to as image scanner is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image, (Wikipedia).
Scanning modes and preferences
Common scanning modes and preferences a user can employ or choose from when scanning documents and images are Line Art, Greyscale, and Colour scanning. However, the scanning preference to be used is largely dependent on the type of document or image a user wants to scan. Line Art - this preference is often used when the graphic is black and white, without an identifiable shade of gray. The line art is relevant for sketches, cartoons, blueprints, diagrams, black and white logos. When the image or file scanned is in black and white in line art, lots of space is saved. This is primarily because a pixel can only be black or white; as a result, the computer doesn't need to store lots of colour information. This means that the higher the colour, the more space consumed. Greyscale - when graphic has shades of grey as well as black and white, grey scale is usually the appropriate preference to be used in the scanning process. Greyscale scanning records up to 256 shades of grey, and so the transition from white to black is smooth. Because of these varying shades of grey in the greyscale preference, scanned images are much bigger than those of the line art. Colour - colour preference is normally used when scanning a colour graphic, photograph, image, and document. In scanning colour images, each pixel stores one of millions of different colours. As a result, coloured scans occupy most space in the storage device, (Virtual Training Help Centre, 2002).
Scanning resolution
The type of selected scanning resolution determines the quality of images, texts, and documents when they have been processed. Virtual Online Help Centre (2002) defined resolution as ‘a measure of how clear and sharp an image is’. Scanning resolution is measured in dots per inch (dpi). A dot per inch is a printer resolution (hard copy format). In the digital world, the appropriate term used is pixels per inch (ppi), but the term dpi has been adopted by many people to represent digital resolution, even though dpi and ppi are used interchangeably. Virtual Online Help Centre (2002) identified that when a scanner scans a graphic or a digital camera takes a picture, the image is stored as a pattern of discrete dots. Each dot stores information about the graphic, which results to the increase of the dots. As the dots increases, the inch also increases; therefore, the more information stored, the more the image file.
The type of scanning resolution to be used is largely dependent upon what a user plan to use the scanned image for. Virtual Online Help Centre (2002) highlighted some rough guidelines for choosing a scanner resolution. - 72-100 dpi for images that will be viewed on a computer screen (e.g., web graphics). - 250-300 dpi for images that will be printed on an ordinary inkjet or laser printer. - 600 for a very high-quality printer or for commercial printing. - 300-600 (or more) if you want to enlarge or edit the image. - 600 or higher for archiving for future use (a user can reduce the resolution at a later time, but cannot add any resolution).
Colour depth
When scanning an image, colour depth or bit depth is used to select or to represent the colour of a single pixel in a bitmapped image or video frame buffer. Unlike scanning resolution which is in dpi or ppi, colour depth is calculated in bits per pixel (bpp) (Wikipedia, 2007). Using a high colour depth provides large range of several different colours. In the course of scanning an image, bits increases and the number of colours becomes too large for a colour map. So in higher colour depths, the colour value typically directly encodes brightness of red, green, and blue to specify a colour in the RGB model. However, the RGB colour model is a colour model in which red, green, and blue light are added together in various ways to reproduce a broad array of colours. The term RGB is derived from the initials of the three additive primary colours of red, green, and blue. Its main function is for the sensing, representation, and display of images in electronic systems, such as televisions, computers, conventional photography, and can also be used in scanning images.
There are different bit colours identified by Wikipedia, 2007. The following are predominantly used when scanning texts, images, and documents with a scanner: 1-bit monochrome (black and white of 2 colours) 8-bit greyscale (4 colours) 8-bit colour (256 colours) 12 bit colour (4096 colours) 15/16-bit colour (High Colour of 65,536 colours) 24-bit colour (True Colour of about 16,777,216 mixed colours) 32-bit colour (Deep colour of about 4.2 billion distinct colours) There are other types of colours available, but are specifically for high level graphics and computer workstations, as well as industrial uses. These colours include 36-48 bit colours, which are also deep colour like the 32 bit.
Types of scanner
There are several types of scanner but the following scanners identified by Wikipedia can suffice:
Drum Scanner: The drum scanners make use of the Photomultiplier Tubes (PMT), to capture the images. Photomultiplier tubes (PMT), are sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum. Reflective originals are placed on an acrylic cylinder, the scanner drum, rotating at a high speed while it moves, scans the object in front of precision optics that deliver image information to the PMTs. Drum scanners have capacity to reproduce scans that are of high quality in resolution, color depth, and value structure. More so, because drum scanners are capable of producing resolutions of up to 12,000 pixels per inch (PPI), they are usually used for enlarging images during scanning processes. The origin of the name drum scanner was from the clear acrylic cylinder, the drum, on which the original artwork is mounted for scanning documents and images.
Flatbed scanner: This is composed of a glass pane (or platen), under which there is a bright light (often xenon or cold cathode fluorescent) which illuminates the pane, and a moving optical array in CCD scanning.
Hand scanners: these come in two forms of document and 3D scanners. Hand held document scanners are manual devices that are dragged across the surface of the image to be scanned. Normal hand held scanners have a small window for viewing the document being scanned. Though use of handheld scanner is gradually running out, 3D scanners are more popular in industrial design, reverse engineering, inspection & analysis, digital manufacturing and medical applications.
