A scanner is a device of optical reading that allows you to convert images, photos, illustrations and texts on paper, in a format digital can be manipulated in the computer. For example, it is possible to to “pass” a cover of a magazine, or a picture to the screen your PC. There are several types of scanners on the market, that use multiple types of technology. This article will show you a little of the operation of the scanners, and the technologies used. The information provided here can help you out in time to get a equipment of this type. The the most common is the flatbed scanner, which looks a lot like a machine copier. Other types are: the scanner drum, hand scanner, scanner barcode reader, scanner and page scanner for business card.
All scanners are based on the principle of reflectance of light, that is to place the image so that a light to light up. A sensor captures the light reflected by the figure, thus forming a digital image. The scanners that are simplest to use fluorescent lamp to illuminate the image, while the more sophisticated use a lamp type cathode-cold. However, another determining factor for the quality of scanned images, is the sensor. Below there is a description of the types of sensors most commonly used:
Photo Multiplier Tube (PMT): used in the drum scanners, which are more sophisticated and expensive. This type of scanner is used mainly in the printing industry, for printing high quality. To scan the image, the same is put into a glass cylinder that rotates at high speed around the sensor PMT, that divides the reflected light into three beams that pass through filters and generate the scanned image. Due to its complexity, the scanners drum are practically only used in applications professionals;
Charge Coupled Device (CCD): this sensor is used in almost all scanners domestic, the most common. Its highlight is good quality and low price. The CCD sensor is used including, in FAX machines, and digital cameras. This type of sensor turns the reflected light into electrical signals which in turn are converted into bits through a circuit called a converter the analog-to-digital. The scannerd table usually have several CCD sensors arranged in a straight line;
Contact Image Sensor (CIS): this type of sensor uses a series red LEDs, blue and green to produce white light and replace the mirrors and lenses used in scanners with a CCD sensor. This allows you to a scanning-more light and uses less energy. However, the quality of the scanned image is not as good as that of the CCD, but enough for simple applications. The price this type of scanner is quite low.
Operation of the scanner drum
For scan images with high quality standard, use of the expensive drum scanners (see the photo on the right). In this type of scanner the image to be scanned is attached to a drum of glass (hence the name). With the revolutions of the drum, the image is read line-by-line through a tubephotomultiplier instead of a CCD. Then, a strong point of light it is focused in the image and its reflection is measured by the tube.
These tubes allow for the scanning of high quality, including settings greatly improved and many details in the shadows.The dynamic range of them is so high that they can capture both deep shadows and highlights very bright and also capture subtle differences in shading. The resolutions of drum scanners, exceeding 12.500 dpi (such as the scanner of figure to the side). If you need a day of a scanner drum, can use it in establishments (such as graphics for example), that charge for the scanned image. This is because in addition to being very expensive, a scanner drum also has high maintenance costs.
A curious fact is that the resolution of the scanners drum allow you to achieve resolutions and quality image so high, that manipulate the resulting file from scanning on a computer (or even a workstation) it is tricky, because the size that the image file takes. It is, in fact, you need a computer with enough capacity to this.
Resolution
The resolution of the scanner defines the richness of detail that the device is able to capture. The measurement is made in dpi, which means dots per inch. The higher the value scanner dpi, the more detailed the picture is scanned. The scanners more simple have a resolution of 300 x 300 dpi, that you want to say, 300 dpi horizontal by 300 dpi vertical.
Another term that is also necessary to know is the pixel (picture element), or element of the image. A digital image it is divided into rows and columns of points. The pixel consists in the intersection of a row with a column.
A flatbed scanner usually has an element of the CCD sensor for each pixel of the image to be scanned. So a scanner that accepts papers with a width of 8.5 inches and with optical resolution of 600 dpi, it has a sensor with 5100 elements in the CCD (600 x 8.5). These elements of the sensor form the read head of the scanner.
The reading head of the scanner is mounted on a structure that slides on a rail to scan the entire image, because if she was fixed only able to scan a single line of the figure. While it seems to be a continuous movement, that is, the head of reading “going down” by the paper, in the truth that happens are small “jumps”, line in line, at the time of scanning the image. Such jumps are executedfor a small motor known as a stepper motor. When it says that a scanner has optical resolution of 600 x 1200 dpi, we are saying that the scanner has 600 dpi in the head of the scanner and that the stepper motor can advance 1200 “jumps” by inch.
Interpolation
The scanners that use CCD sensors, usually have a resolution the optical maximum of 600 x 1200 dpi. However, there are the scanners that work with resolutions of 2400, 4800, To 9600 dpi or more. This is possible thanks to a technique call Interpolation. This is a software (usually present on a chip scanner) will be able to increase the resolution. The resolution obtained is then referred to as the resolution interpolated. The software interpolation does is create new points between the pixels obtained by the resolution optical the original. The problem is that this technique does not it is as precise as the optical resolution. This is because the software is a kind of assumption where new pixels can be added, but this process is not always gives the right. The scanner calculates new points based on the pixels that the same can’t see. There are programs, such as PhotoShop that also make interpolation of images.
Color depth
The first scanners that have emerged only distinguish colors in shades of grey. When an image is scanned, the unit makes pixel the pixel. For each of these pixels, the scanner assigns a certainamount of bits. The higher the value of each pixel, the greater will be the quality of the scanned image. The scanners “the pioneers” only allocate one bit per pixel, which only allowed to work with black and white.
Most scanners today use at least 24 bits to represent the possible colors of a pixel. This allows the scanner to work with up to 16.7 million colors. This amount also it is called “true color”. The number of bits used to represent the color of a pixel is called the depth color.
Types of connection with the computer
See below, the most common forms of connection of the scanner to the computer:
– Connection for parallel port: most of the scanners existing make your connection to the computer through the parallel port. This type of connection is widely used, since practically all the PCs have a parallel port. The majority uses parallel ports common, but there are models that need special types. This means that there is more than one type of the parallel port. One of them is the EPP (Enhanced Parallel Port). Another is the ECP (Extended Capabilities Port). Both have higher speed for data transfer and can travel in both directions, that is, the transmission is two-way. The vast majority of the PCs has a parallel port that works with all three forms: normal, EPP or ECP. So, if the scanner needs port EPP or ECP, simply make the change in the Setup of the computer. This task is somewhat dangerous to the user the laity, therefore, seek the help of someone specialized if not you have enough experience for this action;
– Connection by the USB port (Universal Serial Bus):many peripherals make use of the USB standard. One of them is the scanner. If your computer has USB input, the installation the scanner comes down to the act connects you to the entrance. Is the type of installation easier and is the ideal choice for home users;
– Connection for the SCSI interface (Small Computer System Interface): The scanners that use SCSI interface exist for a long time, but are not essential to the home user. The SCSI scanners usually have a high quality and come with accessories extras, such as automatic document feeders, adapters for slides and other, which makes it an option to be used in offices. The installation of this type of scanner it is a little more complicated, since it is necessary to to install a SCSI controller card inside the computer.
