General characteristics of scanners. Troubleshooting tablet scanner. The main characteristics of the scanner

Scanners- devices for automatic reading and input to PC graphical information (texts, graphs, drawings, drawings).

The file created by the scanner is called a bitmap.

To work with the PC scanner, a special program (driver) corresponding to the TWAIN standard must have a special program. If such a driver is installed on the computer, you can work with a large number of TWAIN - compatible scanners and process files with graphic editors that support the TWAIN standard: ABOBE Photoshop, Corel Draw.

There are the following varieties of scanners:

 manual,

 Tablet,

 drum,

 Form scanners,

 Bar scanners.

Hand scanner It is a line of LEDs and a light source placed in a single housing. Moving the mechanism relative to the original is "manually" by the user.

Tablet scanner . Its device provides for moving the scanning head (LED line) relative to the original with a stepper motor.

Drum scanners . In the scanners of this type, the starting material is fixed on the cylindrical surface of the drum rotating at high speed.

Form scanners designed for data entry with standard forms filled with "by hand" (population census, election).

Barcine scanners designed to enter data encoded in the form of a barcode.

Tablet scanners received the greatest distribution.

The principle of operation - the beam of light, reflected from the surface of the material, is fixed by special elements (CCD) - instruments with charged bond.

The main consumer parameters of tablet scanners is:

 resolution,

 Connection type

 Dynamic range

 Performance

Reading occurs with a CCD matrix. The CCD matrix scanner is made in the form of a ruler, the cameras are in the form of a field. The more items are in the CCD matrix, the better.

The resolution is determined by the number of PZD elements per 1 inch. A typical indicator for office application 1200 - 2400 DPI (Dots Perinch) - dots per inch, for professional graphics 4800 * 9600.

The bit (color depth) indicates how accurate information about the scanned point is. Sufficient color is 48 bits - 16.8 million colors.

The dynamic range of the scanner is characterized by its ability to distinguish the nearest shades. The dynamic range is defined as a logarithm of the brightness of the brightstones and the most dark. A typical indicator for office scanners - 1.8 - 2.0.

The scanner performance is determined by the speed of scanning a standard sheet of paper and depends on both the mechanical part of the scanner and the type of interface.

Graphic tablets (digitizers) are designed to enter artistic graphics information. It is based on the fixation of the pen relative to the tablet.

Digital cameras, like scanners, perceive graphic data using a CCD combined into a rectangular matrix. The main parameter is a resolution, which depends on the number of CCD. Currently, the best models have up to 10 million pixels. Firms: Olympus, Nikon, Minolta, Canon (zoom-zoom to 7 times).

The matrix printer generates signs with multiple needles located in the printer head. The paper is drawn with a shaft, and the painting tape is located between the paper and the printer head. Currently matrix (needle) printers are applied less and less. Advantages of these printers: satisfactory print speed and universalityThe ability to work with any paper, as well as the low cost of writing. Disadvantage: Low quality printed products, especially graphic. Color printing is impossible. Another disadvantage: a needle printer is a mechanical device, and the operation of mechanical nodes is always accompanied by noise.

Inkjet printers

In jet printers, the image is formed by microscopic drops of special ink, flying on paper through small holes. Pugerystals are used as elements that push the ink jets (Fig. 2.9).

Fig. 2.9.

Laser printers

Laser printers currently provide the best print quality. However, colored laser printers are very expensive, so the printing on laser printers is usually black and white. In black and white laser printers, a laser beam is used, controlled by a computer (Fig. 2.10).

The main parameters of laser printers include:

• resolution, DPI (DOTS PER INCH - dots per inch);
• performance (per minute pages); Laser printers with average features printed 6-10 pages per minute. High-performance network laser printers can print up to 20 or more pages per minute. Of course, these are conditional figures, since on the same printer, printing complex graphic images will take much more time than printing text;
• the format of the paper used. Most laser printers can print on A4 format paper, less common - A3;
• the volume of its own RAM. The laser printer processes entire pages, which is associated with a large number of calculations. Most often in black and white laser printers, memory is used from 2 to 16 MB.

Scanners

New term

Scanner (Scanner) - A device for copying graphic and text information in order to enter it into a computer. Scanners are three types - manual, tablet and drums.

Manual scanners - This is a relatively inexpensive device of small size. You often see them in stores, at the checkout. They serve there to read the barcode with the price of goods. The disadvantages of the manual scanner include the dependence of the scan quality from user skills and the impossibility of scanning relatively large images entirely.

IN drum scanners The starting material is fixed on the cylindrical surface of the drum rotating at high speed. The devices of this type provide the highest resolution in the 2400-5000 DPI range. Currently, drum scanners are mainly used in typographic production.

For home users and in offices are most often used tablet scanners (Fig. 2.11).

Tablet scanners are designed to enter graphic information from a transparent or opaque sheet material. Their standard format is A4, so under the cover of such a scanner "face" on the glass can be laid not only a separate sheet or page, but also a whole unfolded book or magazine. These tablet scanners resemble copiers. The main elements of the scanner are semiconductor laser and semiconductor photodetector.

The principle of operation of these devices is that the beam of light, reflected from the surface of the material (or the transparent material of the transparent material), is fixed by special elements called the instruments with the charge relationship (CCD). When the scanner leads in the text or image, the laser beam runs on the sheet, scans it and reflects the photosensitive semiconductor element. The photocell converts the light signal into the electrical, which is then transmitted via the bus to the computer. In it, the signal is converted into a digital form containing information about the coordinates and the color of each pixel image. And finally, at the last stage, the information about the image is recorded on the disk as a file.

Specifications of scanners

In order to properly select the type of scanner, and accordingly, to maximize its ability to implement the tasks, it is necessary to understand the technical characteristics of the scanners and the existing terminology.

• Resolution is the main characteristic of the scanner. In the process of scanning, the image is divided into separate points, the size of which is determined by the features of the optical system and photocells. Under the optical resolution, the number of such points that fit on the segment of a certain length is implied. In the specifications of the device, various resolution values \u200b\u200bcan be indicated horizontally and vertical. For example, the parameter 300? 600 dpi means that each square inch image is broken by 300 points horizontally and 600 vertically. The greater the permission, the more information about the original can be entered into the computer and subjected to further processing.
• The scanner performance is characterized by the duration of scanning a sheet of paper of a standard format and depends on both the perfection of the mechanical part of the device and on the type of interface used for pairing with the computer. In the basic models, the connection of the scanner is used more often via the USB port. In professional scanners - SCSI.
• The dynamic range of the scanner is determined by the logarithm of the brightness ratio of the most light areas of the image to the brightness of the most dark areas. A typical indicator for office scanners is 1.8-2.0, and for professional scanners - from 2.5 (for opaque materials) to 3.5 (for transparent materials).
• The scanner color depth reflects the discharge of an analog-to-digital converter, that is, this feature showing how accurate information about the color of each point of the scanned image. Color depth in 1 bit corresponds to the black and white mode of the scanner operation, each point can only be black or white. In gray mode, the depth of color is usually 8 Bit. This corresponds to 256 grades of gray. This is the number of shades possible for each point. Color scanning is nothing but scanning in gray mode with different filters (red, blue, green). 256 shades for each component of three are given in the amount of 16.7 million possible combinations of colors (24-bit image). It would seem that 24 Bit is enough to accurately transmit any shade, however, with further adjustment of the gamma, brightness or contrast, the palette size decreases significantly, especially along the edges of the spectrum, part of the data is lost. It is for this reason that the host manufacturers already produce models with a color depth 36 and even 48 Bit. With the inevitable loss of data "Spare" bits allow you to obtain a real 24-bit image.

Hello, dear readers! Welcome to mine. In this post, I brought general information about tablet scanners and their main characteristics.

Scanners are one of the most common peripherals of the computer. The main area of \u200b\u200btheir application scanning printed originals, such as old photos, pages from books and magazines, drawings and illustrations. The most common is tablet.

What is a tablet scanner?

If you take in general, the scanner is a device for creating a digital image of a material object. The tablet scanner is named so due to the glass plate tablet, which is located the scanned original. His colleague, drum scanner, uses a glass drum for these purposes. The advantage of the tablet scanner before the same drum is that it is enough to just place the original to the tablet, without exposing it to any effects (pressure, bending, deformation, vibration). Therefore, it is suitable for fragile or even three-dimensional objects.

Device

The most important component of the tablet scanner is a photosensitive element - CIS or CCD matrix. It is fixed in a movable carriage, together with the optical system and the light source. The scanner operation illustrates the picture below. When scanning, light from the source (1) falls on the scanned surface, it is reflected from it, and using the mirror system (2) and lenses (3) falls on the matrix sensors (4), where it is converted into a series of electronic signals.

Dimensions

The sizes of tablet scanners vary depending on the scope of application. Most of the home and small office scanners can scan the originals with a maximum size of 8.5 modes by 11 inches (LETTER or A4 format sheets). Larger tablet scanners are adjacent under the sheets of TabLoid format and can scan the originals from 11 by 17 inches, up to 12 by 18 inches. Such models are often used in the visual studios and in printing for prepress preparation of layouts.

Resolution

The scanner resolution largely determines the quality of the resulting scan. It shows how many points the line of the scanned image of one inch long during digitization is broken, and is measured at inch (DPI) points or pixels per inch (PPI). The characteristics of the tablet scanner indicate the resolution for the two coordinate and u. For example, if the scanner provides 4800 points per inch horizontally (coordinate x) and 9600 vertical (y coordinate), then it is said that the resolution of this model is 4800 to 9600 DPI. Although many manufacturers reduce this indicator, pointing in characteristics only horizontal resolution.

What permission is enough?

When it comes to resolution, no longer always means better. Tablet scanners with high resolution are more expensive. Therefore, not to overpay, it is worth determining what permission you need. The higher the quality of the scan, the higher the print quality, especially on large formats. In this case, the digitized image file will also be very large.

The 4800 DPI resolution is required for high quality printed product. But the printer or the press that will be used for printing is still the determining factor in the quality of the final product. Not all output devices can print in high resolution, so the high resolution of the tablet scanner when scanning may be useless.

If scanned images are planned to be used for viewing on the monitor screen, the high-end scanner is also not required.

Good universal scanners with a resolution of 2400 dpi are quite sufficient for home use. If work is planned only with text originals (for example, with office documentation), it is quite enough to resolve 600 DPI.

Bit depth of color

Another important characteristic of tablet scanners is the bit depth of color. The higher this indicator, the greater the number of colors and shades can be obtained when scanning. The bulk of cheap scanners has a color depth of 24 bits, while a more expensive model of 48 bits. A 24-bit color scanner will be good for color graphs and diagrams. If you scan a lot of photos, it is better to use devices with a color depth of 48 bits. Tablet scanners with a depth of 96-bit can distinguish the widest range of colors and shades, and are used by professionals for scanning paintings and other original works of art.

Price range

Prices of tablet scanners depend on their size, resolution, scanning speed and color depth. They can vary from less than 100 dollars per simple scanner, for home use, up to $ 50000 per high-class professional model.

At the end of the post, I want to offer you an interesting video about the device of the tablet scanner.

Consider the design principles of modern tablet scanners and estimate the values \u200b\u200bof the basic characteristics to be paid to when buying such devices.

A tablet scanner intended for home use is a device, "sharpened" under the solution of two main tasks: the first - scanning of text documents with subsequent recognition, and the second is digitizing photos and other images. Many models of the average price category are equipped with a slide module that allows you to scan transparent originals; Basically, this is a positive and negative film.

To enter the text documents of the scanner alone, the scanner alone is not enough: a special text recognition program is required (the so-called OCR program (from English Optical Character Recognition is "Optical Symbol Recognition") that can save the received data into a text file of a format. One of the best recognition programs are considered to be the Finereader of the Russian ABBYY company. Many scanners sold in our country are equipped with a "lightweight" version of FineReader Sprint. However, individual manufacturers include foreign programs, which to FineReader, to put it mildly, are very far away.

The second task is more difficult. For good digitization of color photography, high-quality optics, matrix and mechanics are needed; In addition, much depends on the scanner driver. Fortunately, modern drivers have a fairly developed graphical user interface, allowing in the scanning process to correct individual defects of the original, including a strongly noticeable raster, insufficient or excessive brightness and even distortion of the color gamma. Many scanners are completed with the simplest graphic editors intended for image processing and, in some cases, to create photo albums. Lovers of drawing or photography will have to learn more powerful packages of Adobe Photoshop or Gimp.

As for the price range, the good tablet scanner of A4 format is from $ 100 to $ 150, and the model is price from 150 to 250 dollars, as a rule, can satisfy the most arring users. Models are cheaper than $ 100 can be viewed only as a budget decision, for with graphics they work mediocre.

Specifications of scanners

The tablet scanner is a flat unit with glass to which the object is mounted to be scanned. There are two types of tablet scanners, which differ in the type of scanning element. The most common type is the CCD line (CCD device with charge / charge) or CCD line. Such an element consists of a plurality of sensors sensitive to the degree of illumination. The line "rides" along the scanned area and decides the information about its illumination. To project an image from a highlighted original on the CCD line, a special optical system is used.

The second kind of tablet scanners - models based on the CIS-line (from the English. Contact Image Sensor - "Pin Sensor Image"). Unlike CCD scanners, a line of LEDs is installed in CIS-models, the width of which is equal to the width of the scanned area. Thereby disappears the need for a complex moving optical system, so such a scanner is much thinner and cheaper than the CCD model.

Both CCD and CIS scanners have their advantages and disadvantages. The CCD scanner requires a separate power supply, and the CIS scanner can be powered through the USB port. CCD scanners are relatively cumbersome, and some CIS-scanners are not thicker than an ordinary book. Nevertheless, I would not recommend buying a CIS-scanner for home, and that's why. The fact is that because in such a scanner there is actually no optical system, the value of the depth of field when working approaches zero. What does this mean? For example, when scanning a thick book, the letter at the scene of the fold for the CIS scanner will be illegible, and when scanning a three-dimensional item is sharp, it will only get it part that is directly pressed to the glass. It is no coincidence that the word "contact" is present in the title. On the other hand, such devices are perfectly coping with scanning of documents on individual sheets, and the quality of color reproduction, contrary to popular belief, is no longer behind the quality provided by CCD scanners. But the lack of depth of field is so narrowing the area of \u200b\u200bapplication of such devices that the CIS scanner home does not make any sense.

Resolution.The characteristics of a typical middle-class household scanner indicate that it works with a resolution of 2400 x 4800 dpi (DPI). What does it mean? In this case, 2400 DPI is a real optical horizontal resolution, which allows you to get the optics and matrix installed in the scanner. 4800 points (or, more precisely, steps) per inch is the so-called hardware or mechanical resolution, which characterizes the accuracy of moving the line with the sensors across the scanned area, that is, vertically. The real permission, of course, will not be higher than 2400 DPI, since optics and the matrix simply will not give the scanner to "see" more due to accurate mechanics. Little of the two values \u200b\u200bspecified in the specification is the optical resolution.

Interpolation resolution is a completely meaningless parameter (as well as a "digital increase" in cameras), since in this case "increased resolution" is achieved by calculating additional points based on the characteristics of their real neighbors. Of course, you will not get more detail, but the file size will grow quite significantly. A real permission of 9600 or even in 19200 dots on an inch on a domestic scanner you will never get, so the numbers of this order indicated on the scanner box for a hundred-two hundred dollars can simply not pay attention to: it is just a notorious interpolation resolution.

Initial-level scanners have an optical resolution of 600 or 1200 dpi, while even 600 DPI permits are enough for the overwhelming majority of tasks, including scanning photos and even amateur slides. Hardware permission can vary from 1200 to 4800 dpi per inch.

Depth or color bit. This parameter characterizes the maximum number of colors that are capable of processing the scanner, that is, it indicates the quality of the color reproduction of the device. In most cases, manufacturers indicate internal discharge, which refers to the capabilities of an analog-to-digital converter (ADC) of the scanner. The overwhelming majority of modern models have 48-bit ADCs, that is, each color (red, green and blue) is described in the scanner of 16-bits of information. However, for non-professional, the 48-bit depth of color is clearly redundant. Even mass graphic editors are usually unable to work with a 48-bit color. Almost the only exception is Adobe Photoshop, and then it is considered massive (for obvious reasons) only in Russia. But even in this software package, to perform the overwhelming majority of editing operations, you have to resort to a 24-bit color (the so-called True Color), and such a discharge at the output guarantees any modern tablet scanner. The high-bit color support is valuable in that it allows you to adjust the image at the driver level.

Dynamic range.The dynamic range (or optical density) suggests how well the scanner is able to reproduce smooth color transitions, as well as how well the device "distinguishes" the brightest and darker fragments of the original. The dynamic range of tablet scanners is very modest, so its value, as a rule, does not indicate, and if they indicate, they are strongly overestimated. At the middle class models, it fluctuates within the borders from D1.8 to D3.0. That is why tablets do not cope well with the scanning of transparent originals and, in particular, negative photographic films that have an increased optical density. Specialized slides-scanners have a dynamic range, as a rule, ranging from D3.2 to D3.6, while the maximum theoretical value of optical density is D4.0.

Scan speed.The speed of the household scanners is not too high, especially when scanning color photographs with a large resolution: this process can stretch for five minutes. Right such devices work only when digitizing text documents.

Interface.If a slow parallel (printer) port and fast SCSI is often used in old models, then modern models are equipped with at least the USB 1.1 interface, and all the novelties are high-speed USB 2.0. Another promising interface - IEEE 1394 (he is Firewire, he is ilink), which has long been present on all Apple computers, as well as on all machines with Creative and Audigy and Audigy family sound cards 2. Actually, there is nothing to choose here, Since almost all middle-class scanners are equipped with a USB interface.

Service amenities.The main thing is to pay attention to, - can the scanner cover close not only subtle originals, but also thick books or magazines. If this opportunity is not, then you will have to press such items to the glass with something heavy, and this is not only uncomfortable, but also fraught with glass damage. Many modern models are equipped with buttons that allow you to get quick access to some functions of the driver (for example, scan to a file, scan and send to a printer or email, etc.), but even their complete absence, as practice shows, not Too affects the convenience of using the scanner.

Slide adapter.Some scanners are equipped with a slide adapter intended for scanning slides and negative film. However, as we talked above, due to the insufficient dynamic range of mass tablets, the results are obtained by mediocre quality. Therefore, if you need to translate your analog photo archive to digital form, it is better to purchase a slide scanner or contact a specialized digital photo laboratory, which appears more and more.

The technical characteristics of tablet scanners in the price range from 100 to 150 dollars differ slightly, so when you choose, you can safely proceed from our own aesthetic preferences, the benefit of all models have a different design, but almost the same features.

On the next page you can get acquainted with some models of tablet scanners presented in the Russian market.

Canon Canoscan 5200f.

The tablet scanner based on the CCD matrix has an optical resolution of 2400 DPI and hardware 4800 DPI, the inner depth of color is 48 bits, external - 48 or 24 bits. The stated dynamic range - D3.3. The device is equipped with a slide module and connects to a PC via USB 2.0 interface. The Easy Color Matching proprietary function provides accurate color reproduction when you print a scanned image on CANON compatible inkjet printers. Complete delivery - OCR program Omnipage SE OCR 2.0. Overall dimensions - 285 x 512 x 112 mm, weight - about 4.1 kg, estimated price - 160 dollars.

Advantages: High resolution, high-speed interface, built-in slide module, colors matching system when printing on Canon printers.

Disadvantages: Large weight, high price.

Epson Perfection 2480 Photo

The CCD matrix based scanner works with an optical resolution of 2400 dpi and hardware 4800 DPI. The device supports a 48-bit color representation (both internal and external) and has the declared dynamic range D3.2. The slide module is built into the apparatus cover. Connection to a computer is carried out via a high-speed USB 2.0 interface. The model is characterized by a very high speed: scanning a color photo of A4 format with a resolution of 300 dpi, that is, with printing quality, it takes, according to the manufacturer, only 15 seconds. The scanner is completed with the FineReader Sprint recognition. Device dimensions - 275 x 419 x 86 mm, weight - 3 kg, indicative price - $ 140.

Advantages: High resolution and speed, high-speed interface, built-in slide module, FineReader Sprint included.

Disadvantages: The complexity of the driver settings in Professional mode.

Genius Colorpage-HR8 Slim

The model from Kye Systems is equipped with a CCD matrix and works with an optical resolution of 2400 dpi; Color depth - 48 bits. The device has a built-in slide module and high-speed USB 2.0 port. The package includes a stand for the vertical scanner setting (storage only), as well as the ABBYY FineReader text recognition program. Interestingly, during the scanning process, the scanner loses the melody. Overall dimensions - 490 x 155 x 390, weight - 4 kg, indicative price - 110 dollars.

Advantages: High resolution, high-speed interface, built-in slide module, stand for vertical installation, ABBYY FineReader complete, attractive price.

Disadvantages: Large weight, "mouse" image of a brand can scare potential buyers.

HP Scanjet 4070.

A model based on the CCD matrix is \u200b\u200bdistinguished by an optical and hardware resolution of 2400 DPI and supports color bit in 48 bits. A slide module is built into the scanner cover. The scanner connects to a computer via USB 2.0 interface. Color photo scanning time of 10 x 15 cm - no more than 25 seconds. The kit comes the I.R.I.S. text recognition program. Readiris. Scanner dimensions - 298 x 472 x 90 mm, weight - 3.29 kg, approximate price - 150 dollars.

Advantages: High resolution, high-speed interface, built-in slide module.

Disadvantages: No FineReader.

Lecture number 7. Tablet scanners

2. Tablet scanners.

1. General characteristics of scanners

Each type of scanners has its own features of application, which causes differences in scanning technology and, therefore, in the characteristics of devices. However, there are some general evaluation criteria for both the scanner itself and the image obtained with it. Consider the overall scanning characteristics regardless of specific types or models of scanners.

Color scanner. Like most other image processing devices, scanners are divided into

Colored;

Black and White (halftone)

Towing black and white.

Colored scanners - the most common view.

Halftone scanners "distinguish" shades of gray, but are not capable of perceiving color images.

Bar black and white scanners distinguish only two colors and are practically not represented in the trading network - they are used mainly on various industries (for example, to scan drawings or barcodes).

Scanner resolution (Resolution) is a set of parameters characterizing the minimum image details that the scanner is able to count. The resolution is divided into optical, mechanical and interpolation.

Optical resolution (optical.resolution) It characterizes the minimum size of the horizontal point, which the scanner is able to recognize. In the scanners using a matrix (for example, tablet or sheet or sheet), this characteristic is determined by the ratio of the number of elements in the matrix line to the width of the workspace. For other types of scanners such as drum) it is limited to the possibilities of focusing light on the phototponder element. Optical resolution - always the smallest of all specified for a specific scanner model, so scanner manufacturers often do not indicate it.

Mechanical resolution (mechanical.resolution) - The number of steps that makes a scanning carriage divided by the length of the path passed by it. Since information is read at each step, the matrix is \u200b\u200bread, this parameter determines the minimum vertical point, which the scanner can recognize. Sometimes mechanical resolution is also called optical, but it is incorrect. For example, if a 300x1200 PPI optical resolution is specified for any scanner model, the optical resolution will be 300 ppi, and mechanical - 1200 ppi. Usually, the mechanical resolution is two times more optical, but there are also models in which it is four times more or, on the contrary, they are equal. Due to the fact that the CCD matrix cannot scan with a resolution horizontally more optical, mathematical interpolation methods are used to add missing points (otherwise the vertical size of any scanned square would be more horizontal). Mechanical resolution is applicable only to scanners with a matrix structure of photodetectors.

Interpolation resolution - Artificially increased resolution with mathematical methods. The program in the package of the scanner is trying to bring an image to this permission by adding missing points (for example, with a real resolution of 3x3, the program issues 9x9). This parameter has nothing to do with the real physical parameters of the scanner and can only be characterized by the image processing program.

The scanner resolution is usually measured in pixel per inch (PPI, Pixel Per Inch). Measure this parameter at inch points (DPI, DOTS PAR Inch) in principle is incorrect, since the actual resolution of the printer is understood under DPI, and this is a slightly different concept. Usually the printer to obtain one color pixel imprints several points, and each of them is responsible for its component color. These points are very close, which creates the effect of one pixel of the desired color: they seem to merge. Accordingly, DPI implies the number of color constituents in an inch. Under PPI, it is precisely the number of full-color pixels per inch.

Bigness (color depth) - A parameter characterizing the number of colors or shades of gray (depending on the chromaticity of the scanner). The bit means how many bits are used by the scanner to represent the color of one image point. There are discharge external and internal. Internal bitty is the number of bits representing a point for internal operations in the scanner (that is, before passing the ADC signal and the transformation into a digital view). External bit rate determines the color of the color after passing the signal through the ADC. The external discharge of scanners is usually 8 bits (256 shades of gray) for halftone scanners and 24 bits (8 bits per component, and only 16.77 million colors) - for color scanners. Internal discharge is usually no less, but more external. Additional bits in internal charge (if any) are used to improve the accuracy of color reproduction and reduce the effects of distortion on color. |

Dynamic range - Another color characteristic. "Quality" of light reflection by any original expresses optical density. It is calculated as a decimal logarithm of the luminous flux relationship falling on the original, to a light flow reflected from the original (for opaque originals) or pass through it (for negatives or slides).

Optical density is measured in OD (Optical Density), or simply D, and can vary in the range from 0.0d for absolutely white (transparent) color up to 4.0d for perfectly black (opaque) color.

Since we are talking about logarithm, for example, 2,0d and 3,0d will not differ by 25%, but 10 times. Optical densities for some types of originals are shown in Table. one.

Table 1. Optical densities of some originals

Original

Range of optical density

Newsprint

Coated paper

Photographs

Negative films

Colored Slides Commercial Quality

High-quality range, film and double slides

The range of optical densities of the scanner indicates which of the original colors will still be recognized, and which - no longer, that is, they will be perceived either as completely white or both absolutely black. The optical density range includes two characteristics: D MIN and D MAX. The first, D min is such an optical density of the original, below which the scanner will consider the original perfect white. Accordingly, D MAX is such an optical density of the original, above which the scanner will consider the original absolutely black. The range itself is the difference D min and D Max. The range of optical densities of the scanner depends on the quality and discharge of the ADC and the photocells, as well as the algorithm for the work of the scanner controller. In tab. 2 These typical dynamic ranges are specified for common types of scanners.

Table 2. Typical dynamic scanner ranges

View, scanner class

Typical dynamic range

Manual scanners

Halftone scanners

Colored tablet scanners, old models and models of the SOHO class

Colored tablet intermediate class scanners

Colored Tablet Scanners High Class

Desktop drum scanners

High-class drum scanners

Working area scanner -Maximum document format that scanner is able to process. The format depends on the design and scanner application. Thus, the document format for leaf-controlled and manual scanners is limited only by width. Conventional home and office scanners most often correspond to A4 formats and adopted in the West format Legal. Professional models may have fixed dimensions adapted for specific originals (for example, a 35-color film slide scanner), or just have a large format - to JSC.

Scan speed - The parameter reflecting the time for which one or another document will be scanned. In fact, this characteristic cannot have any meaning, as it depends on the speed of the computer, the volume of operational memory, from the hardware interface, etc. Therefore, the scanner speed can be evaluated only for a particular workplace. Sometimes this parameter is indicated in the characteristics of the scanner in milliseconds per line.

Scanner hardware interface (Data interface) provides an exchange of information between the scanner and computer. It depends on the data transfer rate between the computer and the scanner. This characteristic can be very important if there is a need for high quality scanned photos (or any other graphic materials). For example, for standard color photographs with a size of 10x15 cm, scanned with a resolution of 720 PPI with a color of 24 bits color (True Color), about 40-MB of disk space will be required. Accordingly, if the data rate between the scanner and the computer is low, then it will have to wait very long. Therefore, the data transmission interface is on the importance of equally with such characteristics as permission and depth of color. Now the market presents scanners with five types of interfaces:

1. Interface LPT. (Standard parallel port Centronics.). This interface is one of the slowest, but also the most simple when installing the scanner: sometimes there are improved options - with support (or even requirement) EPR / ESR. In this case, problems can occur with the installation, since not all computers are equipped with such ports. The LPT interface scanners almost always have a "pass-through port", that is, the scanner does not monopoloys the LPT port, leaving the ability to connect another device (usually the printer is usually connected).

2. Own interface. It is sometimes called ISA. Such an interface is implemented as a separate card with which the scanner can work. Such cards for each scanner model are unique, because of which problems may occur when replacing (if the card, for example, has failed) or after upgrade.

3. SCSI interface - One of the most high-speed data transmission interface. However, if a SCSI card is not supplied with the scanner, then compatibility issues may arise about another SCSI controller. The least problems are created by Adaptec controllers. If your scanner is included in the scanner package, the connection and use of the scanner will not cause problems, but it is not a fact that other SCSI devices will be able to be installed on this controller (for example, due to the lack or incompatibility of the drivers). When the scanner is connected to the SCSI board, the tire matching must be respected, otherwise the devices connected to it will not work normally. The beginning and end of the device chain must be provided with terminators (matching resistances). If there are no external devices on the bus, the terminator can be installed directly on the controller, which serves as the last link in the SCSI chain. Since the scanner is best to install the last in the chain, you need to use your scanner's own terminator, disabling the controller terminator. Most scanners have terminators are inside. Only a few scanners (for example, HP ScanJet 4P) have an external switch.

4. Interface USB - LPT interface successor. The cost of the USB scanner is lower, and the performance of this interface is significantly higher than for a parallel port, but not all computers have USB support.

5. Interface PCMCIA (PC.card) - Interface for working with portable computers. This interface claims universality, but this is not always the case. Therefore, it is worth checking the compatibility of a particular laptop computer with such a scanner.

2. Tablet scanners

Tablet scanners are the most common type of scanners. This popularity is quite deserved: the device of such scanners creates all the amenities when scanning any originals. The original in the tablet scanner is motionless of glass, and the reading in most cases occurs in the light reflected from it. High speed characteristics of such scanners are also an undoubted advantage. This advantage is achieved due to the fact that the photo-element in tablet scanners is not a single photocell, but the reading line of the photocells.

Fig.1. Device tablet scanner 1-original; 2- glass; 3- light source; 4 - mirror system; 5 - lens; 6 - linear photodetector; 7- ADC

In fig. 1 shows a diagram of a device of a tablet scanner. The light bar emitted by the lighting source falls on the original, stretched on the glass. Reflected, light falls on the first mirror from the mirror system. Mirrors are located in such a way that the reflected light gets into a collecting lens. The lens projects the light on the line of photo cells (with magnification). The light that fell on this line is transformed into an electrical analog signal, which further falls into the ADC. In some scanners between the photodetector and the ADC there are intermediate steps operating with an analog signal. These steps are designed for hardware correction of scan errors and, sometimes, the image itself. As a result, the output, that is, the computeter (after the ADC), is a strip of image of the original original.

The scanning procedure described above covers only one image string. Therefore, for the full scan and the head is used. After the scanned pixel row falls into the computer, the carriage shifts one step. The length of this step is fixed and the mechanical resolution of the scanner depends on it (see "General scanner characteristics"). Then the whole procedure is repeated until the specified area is read completely. Consider the described scanner details.

1. Image source. In the diagram, the image source is opaque (the scanner is reflected), but in some cases the transparent original can be used. To work with such documents, the scanner can be equipped with a slide module.

2. Glass plate. Special requirements are presented to the plate: the quality of the glass should be very high, the surface must be as smooth as possible and there should be no inhomogeneities inside the glass. This is despite the fact that the glass thickness is very small.

3. Photo receiving matrix This, and the following details on the list are on the so-called scanning head or carriage). Almost this is the most essential detail of the scanner. From it depend on the optical resolution, dynamic range, the scanner operation scheme (single or three-part) and almost all other characteristics (except for the work area of \u200b\u200bthe scanner). To date, two types of photodifying matrix are most common:

CCD matrix (device with charging relationship, in English notation - CCD, Couple-Charged Device);

CDi-matrix (contact image sensor, in English notation - CIS, Contact Image Sensor).

The basis of the element of the CCD matrices is a phototransistor, made using MOP technology (metal-oxide-co-conductor). This technology is used in many other devices for reading images, from powerful telescopes to night vision devices.

This photo cell is inherent in its advantages and disadvantages. Among the advantages of the CCD, it is necessary to note the following:

High sensitivity. The quantum efficiency of the CCD is extremely high and can reach 95%. For comparison, the quantum efficacy of the human eye is about 1%, the best photoemals have quantum efficiency up to 3%, photoelectronic multipliers (photodetectors in drum scanners) - up to 20%. Quantum efficiency determines the ability of the photodetector to translate light into electrical signals, that is, expresses the effectiveness of the quanta (particles of light) in the electrical signal. Strictly speaking, it is equal to the ratio of the number of registered charges to the number of photons in the photosensitive region of the CCD crystal. The energy of the quantum depends on the light wavelength, therefore it is impossible to clearly designate this characteristic for the CCD - it changes throughout the spectrum and is usually set as a function from the wavelength.

Wide spectral range. The CCD can respond to light, ranging from gamma and X-ray and ending with infrared radiation. This range does not currently give any of the matrix technologies. The main shortcomings of the CCD are:.

Limited permission. In all matrix photodetectors, there is a limitation of maximum resolution by the number of matrix elements.

Noise. There are several types of noise. Some types of noise depend on temperature, so for high-quality CCD sometimes cooling is used. Other types of noise depend on the quality of the CCD assembly. But there are noise that is not able to filter even in the highest quality devices. For example, so noise is photon noise. This noise is a consequence of the nature of light and does not depend on photodemist. All these noises make appropriate distortions into the scan result. Usually distortions are manifested in the form of noise bits. In the younger class scanners for each of the three components of the colors (8 bits per each) two senior bits are "noise" and do not contain accurate color information.

Swaying charge. This effect arises as a result of the fact that the charge accumulated by the PZD element varies linearly depending on the light on it. Accordingly, there is some limit limiting this charge. If, during the illumination, the total number of photons (particles of light) exceeds the limit value, then the charge will begin to "flow" into neighboring pixels. On the resulting image it looks like a blurry of too bright image details.

The fundamental difference between the CD and the CD and the CCD matrix-mi is not. CDI scanners are distinguished by CCD scanners in that the matrix is \u200b\u200bstretched to the entire width of the workspace, so the optical system is completely absent.

However, the device of many other nodes depends on the technology of the photodifying matrix, so it should be noted about the differences in the scanning matrix, but about differences in the scanners.

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