To enter graphic information use scanners graphics tablets(digitizers) and digital cameras. It is interesting to note that using scanners you can also enter symbolic information. In this case, the source material is entered in graphical form, after which it is processed by special software (pattern recognition programs).

A hand-held scanner, as a rule, is somewhat reminiscent of an enlarged electric razor.

In order to enter any document into the computer using this device, you need to move the scanning head over the corresponding image without sudden movements. Thus, the problem of moving the reading head relative to the paper falls entirely on the user. By the way, the uniformity of the scanner’s movement significantly affects the quality of the image input into the computer. Some models have a special indicator to confirm normal input.

The input image width for hand-held scanners typically does not exceed 4 inches (10 cm). Some models hand scanners To increase resolution, reduce the width of the input image. Modern hand-held scanners can provide automatic “gluing” of the input image, that is, they form a whole image from its separately entered parts. This is, in particular, due to the fact that using a hand-held scanner it is impossible to enter even A4-sized images in one pass.

Hand-held scanners are the simplest and cheapest. The main disadvantage is that the person himself moves the scanner around the object, and the quality of the resulting image depends on the skill and steadiness of the hand. Another important drawback is the small scanning bandwidth (up to 10 cm), which makes reading wide originals difficult.

Handheld scanners. The operating principle of hand-held scanners is basically the same as flatbed scanners. The difference is that pulling the CCD line in this case is done manually. The uniformity and accuracy of scanning are provided unsatisfactorily, and the resolution of a hand-held scanner is 150-300 dpi.

Barcode scanner. They are designed for reading barcodes from product labels in stores. Bar scanners allow you to automate the process of calculating the cost of purchases. They are especially convenient in retail premises equipped with electronic communications and making payments to customers using electronic means of payment (credit cards, etc.). The main advantages of hand-held scanners include their small size and relatively low price.

Bar scanners. This type of hand-held scanner is designed to input data encoded in the form of a barcode. Such devices are used in retail trading network.

Desktop scanners. The very concept of “desktop” means that these scanners are located on the table and are installed in a fixed position (they do not need to be moved relative to the document). Such scanners allow you to input images measuring 8.5 by 11 or 8.5 by 14 inches. There are the following types of desktop scanners: sheet-fed, flatbed, sheet-fed, overhead, drum and form scanners.

Sheet-fed scanners allow you to scan a sheet of paper in one operation standard format. The scanning unit of such scanners is stationary, and the paper is pulled past it using special rollers (like in a printer). These scanners guarantee good quality scanning, but they are only capable of scanning single sheets. Convert with their help into electronic form page, books or magazine spreads are not possible.

Sheet scanners. Their main difference from the previous two is that during scanning, a ruler with CCD elements is fixedly fixed, and the sheet with the scanned image moves relative to it using special rollers.

Flatbed scanners The main difference between flatbed scanners is that the scanning head moves relative to the paper using a stepper motor. Flatbed scanners are the most “capable”. Outwardly, they may somewhat resemble copying machines - “copiers”, the appearance of which is, of course, known to many. To scan an image (of something), you need to open the scanner lid, connect the sheet to be scanned onto the glass plate with the image facing down, and then close the lid.

Flatbed scanners. This is the most common type for professional work today. The object to be scanned is placed on a glass sheet, the image is read line by line at a uniform speed by a reading head with CCD sensors located at the bottom. The flatbed scanner can be equipped with a special slide attachment device for scanning transparencies and negatives.

All further control of the scanning process is carried out from the computer keyboard - when working with one of the special programs supplied with such a scanner. It is clear that the considered design of the product allows (like a “copier”) to scan not only individual sheets, but also pages of a magazine or book. The most popular scanners of this type on the Russian market are models from Hewlett Packard.

Slide scanners were previously used to scan slides and microimages. The ability to scan slides is now included in many flatbed scanner models.

The main consumer parameters of flatbed scanners are:

Resolution;

Performance;

Dynamic range;

Maximum size of scanned material.

Roll (roller) scanners

The operation of roll scanners is somewhat reminiscent of the operation of an ordinary fax machine. Individual sheets of documents are pulled through such a device, and they are scanned. Thus, in this case, the scanning head remains in place, and the paper moves relative to it. It is clear that in this case, copying pages of books and magazines is simply impossible.

Projection scanners resemble a kind of projection apparatus (or photo enlarger).

Projection scanners. A relatively new direction. A color projection scanner is a powerful multifunctional tool for inputting any color images, including three-dimensional ones, into a computer. It can easily replace a camera.

The input document is placed face up on the scanning surface, with the scanning unit also on top. Only the scanning device moves. The main feature of these scanners is the ability to scan three-dimensional projections. For example, the Niscan Page combination scanner provides operation in two modes: sheet feeding (scanning originals in formats from business cards to 21.6 cm) and a self-propelled scanner.

To implement the last mode of the scanner, you must remove the bottom cover. In this case, the rollers, which usually pull the paper, serve as a kind of codes on which the scanner moves along the scanned surface. Although it is clear that the width of the image entered by the scanner in both modes does not change (slightly larger than the A4 format), however, in the self-propelled mode you can scan an image from a sheet of paper exceeding this format, or enter a formation from the pages of a book.

Drum scanners provide the highest scanning resolution, but they are primarily designed for scanning transparent materials, such as slides, negatives, etc., rather than paper documents. In this type of scanner, the reading head is mounted stationary, and the image mounted on a cylindrical drum rotates at high speed and is scanned line by line.

Drum scanners are used in professional printing activities. The principle is that the original on the drum is illuminated by a light source, and photosensors convert the reflected radiation into a digital value.

Drum scanners. In this type of scanner, the source material is fixed on the cylindrical surface of a drum that rotates at high speed. Devices of this type provide the highest resolution (2400-5000 dpi) due to the use of photomultipliers rather than CCDs. They are used for scanning source images that have high quality but insufficient linear dimensions (photo negatives, slides, etc.)

And finally, form scanners stand out in a special place. These are special scanners for entering information from completed forms. Some experts consider form scanners to be a type of sheet-fed scanner. With their help, data is entered from questionnaires, questionnaires, and ballot papers. Scanners of this type do not require high resolution, but very high performance.

Form scanners. Designed for entering data from standard forms filled out mechanically or by hand. The need for this arises when conducting population censuses, processing election results and analyzing personal data.

Form scanners are not required to have high scanning accuracy, but performance plays an increased role and is the main consumer parameter.

Nowadays, scanners have another application - reading handwritten texts, which are then converted into ASC II codes by special character recognition programs and can subsequently be processed by text editors.

Introduction

1. Types of scanners

2. Scanner characteristics

3. Software

4. Manufacturers

Conclusion

Literature

INTRODUCTION

Scanner(English scanner) are devices for entering text or graphic information into a computer by converting it into digital view for subsequent use, processing, storage or output.

In 1857, the Florentine abbot Giovanni Caselli invented a device for transmitting images over a distance, later called pantelegraph. The transmitted image was applied to the drum with conductive ink and read using a needle.

In 1902, the German physicist Arthur Korn patented photoelectric scanning technology, which later became known as telefax. The transmitted image was fixed on a transparent rotating drum, a beam of light from a lamp moving along the axis of the drum passed through the original and through a prism and lens located on the axis of the drum hit the selenium photodetector. This technology is still used in drum scanners.

Later, with the development of semiconductors, the photodetector was improved, a flatbed scanning method was invented, but the principle of image digitization itself remains almost unchanged.

1. TYPES OF SCANNERS

Depending on the method of scanning an object and the scanning objects themselves, there are the following types of scanners:

Flatbed scanners are the most common type of scanners, as they provide maximum user convenience - high quality and acceptable scanning speed. It is a tablet with a scanning mechanism inside under transparent glass.

The object to be scanned is placed on the glass of the tablet with the surface to be scanned down. Under the glass there is a movable lamp, the movement of which is controlled by a stepper motor.

Light reflected from an object enters a sensitive matrix through a system of mirrors. The receiving element converts the light level into a voltage level. Next, after possible correction and processing, the analog signal is sent to an analog-to-digital converter (ADC). From the ADC, the information comes out in binary form and, after processing in the scanner controller, through the interface with the computer, it enters the scanner driver - usually this is the so-called TWAIN module, with which application programs already interact.

For each step of the engine, a strip of the object is scanned, which are then combined by software into a common image.

A fluorescent lamp with a light spectrum close to daylight is used as a linear light source, and a CCD (charge-coupled device) line is used as a receiver.

Manual - they do not have a motor, therefore, the user has to scan the object manually, its only advantage is its low cost and mobility, while it has a lot of disadvantages - low resolution, low operating speed, narrow scanning band (up to 10 cm), possible skewed images because it will be difficult for the user to move the scanner at a constant speed.

Sheet-pulling - a sheet of paper is inserted into a slot and pulled along guide rollers inside the scanner past the lamp. It is smaller in size compared to a flatbed, but can only scan individual sheets, which limits its use mainly to company offices. Many models have an automatic feeder, which allows you to quickly scan a large number of documents.

Book scanners - designed for scanning bound documents. Modern models of professional scanners can significantly increase the safety of documents in archives, thanks to very delicate handling of originals. Scanning is done face up. The software used in book scanners allows you to eliminate defects, smooth out distortions, and edit the resulting scanned pages. Book scanners have a unique book de-crease function, which ensures excellent quality of the scanned (or printed) image.

Planetary scanners - used for scanning books or easily damaged documents. When scanning there is no contact with the scanned object (as in flatbed scanners).

Drum scanners - Drum scanners, which are significantly superior in light sensitivity to consumer tablet devices, are used exclusively in printing, where high-quality reproduction of professional photographs is required. The resolution of such scanners is usually 8000-11000 dpi or more.

In drum scanners, originals are placed on the inside or outside (depending on the model) side of a transparent drum. After mounting the original, the drum is set in motion. One line of pixels is read per revolution, so the scanning process is very similar to the operation of a screw-cutting lathe. A focused beam of light passing through a slide (or reflected from an opaque original) hits a splitting system (prism or block of mirrors) and, through three light filters, hits photosensitive elements - photomultipliers.

Halogen or xenon lamps with a power of 30-75 W are used as a point light source, because they combine high radiation intensity with a fairly uniform power distribution over the entire range of the radiation spectrum.

Slide scanners - as the name implies, are used for scanning film slides; they are produced as independent devices or as additional modules to conventional scanners.

Barcode scanners are small, compact models for scanning product barcodes in stores.

3 D -scanners- devices that analyze a physical object and, using the obtained data, create a 3D model. They are used for engineering analysis, control, design, games and entertainment (creating digital character models), medicine and other fields.

Three-dimensional or 3D scanning is the process of converting the physical form of a real object into digital form, i.e. obtaining a three-dimensional computer model of the object.

In order for the scanner to “link” to the object being scanned, special index anchor marks are glued to the object before scanning. The combination of these marks forms a unique coordinate system associated with the object in which the surface is constructed. In the case of an optical scanner, these points are used to glue individual scans together.

All shiny, mirror or transparent surfaces of the object are coated with an anti-reflective compound, creating a white matte surface suitable for optical or laser 3D scanning.

The output from the scanner is a triangular polygonal model of the object.

3D scanners are divided into two types based on the scanning method:

· Contact, this method is based on direct contact of the scanner with the object under study.

Contact 3D scanners are built on the principle of tracing a model with a special, highly sensitive probe; with the help of it, the three-dimensional coordinates of the scanned model are transferred to the computer.

· Contactless.

Non-contact devices can in turn be divided into two separate categories:

· Active scanners

· Passive scanners

Active scanners emit some directed waves (light, laser beam, ultrasound or x-rays) onto an object and detect their reflection for analysis.

Passive scanners do not emit anything at the object, but instead rely on detecting reflected ambient radiation. Most scanners of this type detect visible light, which is readily available ambient radiation.

Ultrasound scanners(ultrasound scanners) – used in medicine to study internal human organs.

The operation of an ultrasound scanner is based on the fact that ultrasonic vibrations, when propagating, obey the laws of geometric optics. Any medium, including body tissues, prevents the propagation of ultrasound, that is, it has different acoustic resistance, the value of which depends on their density and the speed of ultrasound.

Having reached the boundary of two media with different acoustic resistance, the beam of ultrasonic waves undergoes significant changes: one part of it continues to propagate in the new medium, being absorbed to one degree or another by it, the other is reflected. The reflection coefficient depends on the difference between the values acoustic impedance tissues bordering each other: the greater this difference, the greater the reflection and, naturally, the greater the amplitude of the recorded signal, which means the lighter and brighter it will appear on the device screen. A complete reflector is the boundary between tissue and air.

2. SCANNER CHARACTERISTICS:

Original type. Scanning can be done in transmitted light (for originals on a transparent backing) or reflected light (for originals on an opaque backing). Scanning negatives is particularly challenging because the process is not simply about inverting the color gradations from negative to positive. To accurately digitize color in negatives, the scanner must compensate for the color photographic veil on the original. There are several ways to solve this problem: hardware processing, software algorithms for transitioning from negative to positive, or lookup tables for specific types of film.

How to choose the optimal flatbed scanner and learn how to use it, what types there are.

It is difficult to imagine modern life without a computer, which today is used in everyday life, in offices, and in production. There are many ways to expand its functionality peripheral devices. One of them is a scanner, which is used to create a digital copy of a text, graphic or raster document placed on a physical medium (paper, slide, photo and film). The process of digitizing images is called scanning. There are several types of computer scanning devices, the most common of which are tablet-type devices.

• 1 What is a flatbed scanner
• 2 How to choose a flatbed scanner for home and office

• 3 Connecting, installing and using the flatbed scanner
• 4 Flatbed scanner repair

What is a flatbed scanner

The modern computer market is characterized by quite high dynamics. Thanks to the rapid development of new and improvement of existing technologies, it can offer different kinds universal-purpose scanners or equipment designed to solve specific professional problems:

• flatbed scanners, which are the most popular and versatile. In these devices, the original to be scanned is placed on a special glass tablet;
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  A flatbed scanner has a special compartment with flat glass where a document is placed, the contents of which need to be transferred to a computer file

• drum-type scanners, which place a document on a special drum. They allow you to get highest quality images, but have a rather bulky design and a high price. Mainly used in the printing industry;
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  The drum scanner uses a glass drum to place the original, allowing you to scan transparent and opaque source materials

• broaching devices designed for scanning unstitched documentation, in which rollers pull the document past a fixed reading head;
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  In a broach scanner, the original document is moved by rollers past a stationary head with a light source and photosensitive elements

• film scanners used to digitize images from slides and films. These devices have a highly specialized purpose for professional photo studios;
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  A film scanner is used to digitize information from transparent image media in the form of films and slides

• planetary devices in which the original does not come into contact with the working surfaces, which is very convenient when scanning books, bound papers or old old documents;
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  The planetary scanner is an ideal peripheral device for converting books and ancient documents into computer format.

• projection scanners, the movable head of which can be aimed at distant objects;
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  The reading head of the projection scanner is located at a distance from the document being copied

• hand-held scanners that do not produce high-quality copies, but have one very useful property - portability.
• 
  

  Portable hand-held scanners allow you to work with documents anywhere and without being connected to an electrical outlet.

How a flatbed scanner works

The popularity of the flatbed scanner can be explained by its high functionality and ease of use. To convert any document into a computer format, it does not need to be bent or deformed in any other way, such as in drum devices.

The operating principle of a flatbed scanner is as follows:

Device, main components and parts

Like any other computer equipment, a flatbed scanner consists of mechanical and electronic parts and components. It is the presence of electronics that makes it possible to classify it as equipment that is complex in design, although at first glance the inside of the device looks quite simple.

The design of any flatbed scanner includes the following parts and components:

• the case, which is the base of the tablet with a removable lid (it should be quite rigid and can be made of metal or durable polymer materials of high density);
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  The body of the flatbed scanner can be made of metal or durable plastic

• glass that serves as the basis for placing the scanned document;
• a mobile carriage with a scanning head attached to it and a light source, which is a fluorescent lamp;
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  The main actuator of a flatbed scanner is the scanning head, on which a fluorescent lamp is mounted

• stepper motor;
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  The movement of the scanning carriage in a flatbed scanner is ensured by a stepper motor on which a pulling belt is attached.

• a pulling mechanism consisting of a tension pulley, a pressure spring and a toothed belt, which serves to move the carriage with the scanning head along the axis of the tablet;
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  The movement of the scanning carriage in a flatbed scanner is carried out along the Y axis of the tablet

• transport lock, which serves to ensure a stationary position of the carriage during transportation to prevent damage to it;
• power module;
• ADC - a device that converts an electrical signal into a digital one;
• a processor that controls all operating cycles of the device;
• interface module with controllers responsible for transferring data from the scanner to the computer. In modern scanner models, this element can be built directly into the processor.

All types of flatbed scanners that exist today are controlled via a computer, for connection to which there are USB, FireWire or SCSI connectors on the peripheral device housing. In addition, some models may have quick scanning buttons on the body.

The body of the flatbed scanner has quick scanning buttons and connectors for connecting the device to a PC.

The main part of any type of scanner is its matrix. IN modern devices Two types of matrices are used that have different photosensitive elements - CCD, operating on CCD charge-coupling devices, and CIS, which use contact sensors. Not available in CIS scanners optical system mirrors, and the light reflected from the original is captured by self-focusing lenses and sent to contact sensors installed on the same line with them. In such devices it is used LED lights scanned sample. All this makes it possible to make the device body thinner, but the scanning quality, color rendition and depth of field of such scanners are lower than those of devices equipped with a CCD matrix with an optical system.

It is thanks to the higher scanning quality that flatbed scanners with a CCD matrix have become most widespread. But devices based on contact sensors also remain in demand where special resolution is not needed, for example, for sheet-fed digitization text documents. The advantage of such devices is low power consumption and the ability to receive power via USB, which significantly increases their mobility.

How to choose a flatbed scanner for home and office

The modern computer market provides big choice a variety of scanners. To pick up suitable model for home or office use, you need to know the basic parameters by which these devices differ.

First of all, you need to decide for what purpose you are buying a scanner and how important the quality of the resulting image is to you. Typically, at home, this peripheral device is used to digitize photographs and images. In this case, color quality and depth of field will be of paramount importance. To scan text documents, it will be enough to purchase a device with a lower resolution.

When choosing a flatbed scanner, you should first pay attention to several basic parameters.

• Permission. This is the main indicator that determines the quality of the resulting image. It is expressed by the number of pixels (ppi) or dots (dpi) into which 1 inch of the image will be divided when scanned. The more points the scanned document is divided into, the higher the quality of the resulting digital copy. In the characteristics of scanners, this parameter is indicated by two numbers indicating horizontal resolution ( optical resolution) and vertically (mechanical resolution). Sometimes only the optical resolution is indicated, which depends on the matrix used. Typically, to obtain a high-quality digital copy for home use, a scanner resolution of 600x1200 dpi is sufficient. But if in the future you plan to process the resulting image in one of the graphic editors, then you should choose a scanner with a resolution of at least 2000 dpi. In any case, it is irrational to buy a device with a resolution that exceeds that of other peripheral devices, for example, a printer.
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  The higher the scanner resolution (the higher the number of dots per inch), the clearer the outlines of the letters on the resulting document.

• Color rendition or bit depth. This parameter in the technical data sheet of a flatbed scanner is indicated in bits: the larger it is, the more clearly the colors and shades of the original document will be transmitted when scanning. For scanning text documents, as well as color charts and graphs, a 24-bit scanner will be sufficient. If you plan to digitize images and photographs, then it is better to purchase a 48-bit device. Flatbed scanners with a color rendering depth of 96 bits are classified as professional.
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  The greater the color depth, the greater the number of shades and colors the scanner displays and the higher the quality of the image obtained as a result of scanning.

• Dynamic range. For non-professional models, this indicator is often not even indicated in the passport, but it significantly affects the number of gradations of image brightness, ensuring a smooth transition in its adjacent tones. For a 24-bit color scanner this figure should be in the range from 2.4 to 2.6 units, and for a 48-bit scanner it should be at least 3.
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  The higher the scanning dynamic range, the richer and more contrasting the resulting documents are.

• Format of the scanned document. Most modern flatbed scanners for home use and office purposes are designed for documents of A4 size (210x297 mm). Larger format devices are used to create layouts in printing or for art studios and are already classified as professional.
• Type of connection to the computer. Most flatbed scanners produced today can have three types of ports for connecting to a PC - USB, SCSI, or a combined USB + SCSI. It is best to buy a device with the most popular interface today, which is present on the vast majority of computer equipment - USB.
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  It is best to buy a scanner that has a USB connector, which is most often found in modern computer technology.

• Supported operating systems. Since any scanner is only a peripheral device for a PC, it must support the operating system installed on it. An excellent choice for purchase would be a multi-system tablet device that will not tie you to a specific OS, and you can right moment change Windows to Linux or Mac OS.

When choosing a flatbed scanner, its additional functions. One of them is the ability to use an automatic sheet feeder. This option will not be superfluous for an office where you plan to scan a large array of single unbound documents.

The presence of an automatic feeder for scanned documents significantly increases the speed of the scanner, which can be useful for an office with a large volume of document scanning work

There are also scanner models with the ability to connect an external module for scanning film and slides. Of course, it is not capable of producing such a full-fledged high-quality digital print as a film scanner, but it will be quite sufficient for creating a home photo archive on a PC.

The presence of a film scanning module in a regular flatbed scanner will help you save on buying an expensive film device for your home

Connecting, installing and using the flatbed scanner

Before you start using the flatbed scanner, you need to connect it to your computer and install it on HDD PC corresponding software. Without it, the computer simply will not recognize the peripheral device connected to it.

Typically, drivers and utilities necessary for operation are included with the device on a special disk. They must be installed on a computer without connecting a scanner to it. To do this you need:

• Insert the boot disk into the computer's CD/DVD drive and wait for it to autoboot.
• If the driver download has not started, go to the “Start” menu - “My Computer” and click right click mouse on your disk drive icon. You can select “Startup” from the menu or download required file manually - such files are usually indicated by the symbols setup.exe.
• If your scanner does not come with an installation disk, necessary drivers and utilities can be downloaded from the official website of the flatbed scanner manufacturer.

Only after this will the computer begin to recognize the connected peripheral device and be able to fully work with it. It remains to check the operation of the scanner. To do this you need:

A program for scanning images is already available in operating system computer. Having installed a graphic editor, you can send scanned photos from the scanner directly to it and work with them further. But to process a text document, you will need to install a text recognition program on your PC. It can be found on the Internet and installed in the same way as it was done for scanner drivers.

Video: installing the scanner

How to use a flatbed scanner

You can scan images without installing additional programs on your PC. To do this you need:

• Place the document to be scanned under the flatbed scanner cover, face down.
• Open the scanning program installed on your operating system by using the Start menu, selecting All Programs and launching the Windows Fax and Scan application.
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  To open the standard scanning program, you need to select “All Programs” from the Start menu and find the “Windows Fax and Scan” item in the drop-down list.

• In the window that opens, select a new scan.
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  To start the scanning process in the program integrated into Windows OS, you must select “New Scan” in the upper left corner of the panel

• When the dialog box appears, specify the scanner and scanning parameters.
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  In the next dialog box of the program you need to select a scanner (several of them can be installed) and its operating parameters

• By clicking on the “Scan” button, wait for the process to complete. After the name of the scanned image appears in the list located at the top of the program window, right-click on it and call context menu and select the required action.
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  After the scan is completed standard program Windows, you must select an action to perform with the scanned image

To be able to perform any actions with a digitized image, you need to download and install additional programs on your PC. The most popular of them is ABBYY FineReader. In some flatbed scanner models, such a program is supplied along with drivers for boot disk. It significantly expands the possibilities of working with scanned texts.

The procedure for working with FineReader (as well as with other similar applications) is similar to working with a program integrated into Windows OS, with the only difference being that in the first dialog box you should select the action that will need to be performed after the scanning process is completed.

When working with ABBYY FineReader, before selecting scanning parameters, you must define the final task in the pop-up dialog box

Flatbed scanner repair

Repairing flatbed scanners is a very responsible task that requires special knowledge and skills. A scanner is an electronic computer device, the cause of failure of which may be a malfunction of the mechanical or electronic part, as well as a failure software. For diagnostics, you will need special equipment, an oscilloscope, a multimeter, as well as knowledge from the field of electronics.

Typical failures of flatbed scanners are:

• malfunction of the lamp, its burnout and the appearance of dark spots that reduce the flow of light. This problem can be solved by replacing the lamp;
• Scanning head is clogged. To eliminate the defect, you will need to clean the mirrors, lamp and other elements of the scanner optics;
• Stepper motor malfunction. Restoration work or replacement of this unit will be required;
• malfunctions of the moving parts of the scanner. They are often eliminated by carrying out preventive cleaning, lubrication, and in some cases, replacing gears with increased mechanical wear;
• failure of the power supply. Usually it is replaced with a new one;
• USB connector malfunction. It can be eliminated by soldering the wires or replacing this assembly part.

Not so often, but there are also electronic malfunctions that require replacement individual elements or whole boards.

In most of the above cases, for repairs you need to contact a specialized service center. But still, one of the most common scanner malfunctions can be fixed independently. We are talking about replacing the lamp. Modern flatbed scanning machines use fluorescent lamps cold glow. Over time, darkening appears on them, which most often occurs in the end part, where the electrodes come from. This results in defects in the scanned image.

You can diagnose the presence of defects on the lamp by lifting the cover while the scanner is turned on. An uneven and dim glow will indicate a malfunction of the light source. To replace the lamp you need:

Video: Removing the flatbed scanner glass

Disassembling a flatbed scanner is also necessary in cases where it is necessary to carry out preventive cleaning, remove debris that interferes with the movement of the carriage, or replace a damaged cable. Depending on the model, disassembly methods may vary. In some scanners, you may need to unscrew the screws in the area where the tablet cover is attached, and then simply slide the frame with the glass, removing it from the grooves.

Video: disassembling a flatbed scanner to clean the glass

In other models, you need to turn the scanner upside down and carefully use a screwdriver to open the frame of the tablet with the glass where it is attached to the latches.

Video: how to disassemble a scanner with a tablet fastened with latches

Flatbed scanners are the most versatile of all such peripheral devices. They are used for digitizing both individual sheets and fairly large books. Today this is the most popular and popular type of scanning technology, the quality of the resulting image is close to the simplest models of drum devices, but is much more compact and cheaper. Possessing necessary information about the design, principle of operation and basic operating parameters of flatbed scanners, you can easily select the appropriate model for home use or office and learn how to scan any documents.

2018-01-15

A scanner is a specialized device that is used to convert images of a selected surface into digital form. Such surfaces can be pages of books, magazines, notebooks, photographs, slides and other documents with graphics and text data. Scanning devices can operate as a peripheral to a PC or as a standalone device, that is, they can independently transmit the scanned image over global network or wi-fi.

Scanning technology first appeared in 1857 thanks to the Florentine abbot Giovanni Caselli. He created a pantelegraph device that transmitted images over wires. When received, it was applied to the drum using conductive ink, then read by a needle. Five years later, the photoelectric scanning principle was patented. Later, a device using this technology began to be called a telefax. Modern scanning devices have undergone significant changes; they have become an order of magnitude more efficient and productive.

Kinds

The scanner can be:

• Industrial use.
• Household use.

Industrial ones are used in various industries. They are subject to high demands in terms of speed, scanning quality, reliability and other operating parameters, because they are designed for constant operation. Homemade ones are rarely used, as a result of which they are cheaper and less productive. However, in Lately devices for the home are produced that are not inferior to industrial ones in scanning speed.

By area of ​​application, scanning devices can be:

• Tablet version. It is the most popular in household use. In this case, the object to be scanned is placed on a glass tablet. A photoelectric carriage with optical elements moves across the tablet, and the image being read is converted into a digital code. Tablet models are usually inexpensive, lightweight and easy to use.

• Film version. This is a specialized device that is used only for scanning transparent objects, for example, transparencies, negatives or slides. Devices of this type are often used by studio employees or professional photographers. Such devices are rarely used in everyday life, as people prefer to use the services of photo studios.

• Drum version. In it, the scanned image is installed on a rotating drum. The digital image is captured by a beam as the drum rotates. Such devices provide very high picture quality. However, they have a high cost and large dimensions, as a result of which they are used only by large companies. They are mainly used in printing.

• Drawing. Such devices are used for unbound documents. They are often called document scanners, because they make it possible to automate the scanning of significant volumes of office documentation. The principle of automatic sheet feeding works here. The system ensures that the scanned materials are pulled through a photo-reading system, which is why they are often called in-line. However, such devices are not capable of scanning stapled sheets.

• Flatbed-broached are a combination of broaches and flatbed devices.

• Passport. These devices are adapted for scanning driver's licenses, passports and other identification documents. They stand out for their compactness and good scanning speed.

• Planetary. Provide contactless scanning of magazines and documents. These devices are often used to digitize originals that require a delicate approach, for example, historical documents that have not been spared by time.

• Network. They are connected directly to the network infrastructure without the use of a PC. Thanks to this, each company employee can scan documents and send them via e-mail or saving it to a network folder.

Device

A book scanner has the following main elements:

• The scanning head is located at a small height above the image. In most cases, it is designed as a scanning ruler and scans from one end of a book or magazine to the other.
• A number of models have a book cradle, which is required to ensure that the height of the book surface is level. Pressure glass can be used to smooth out and reduce distortion. V-shaped cradles can be used for books.
• The heads often contain matrices that are similar to the matrices of digital cameras. With these units, scanning is carried out during the period of opening the shutter, which allows you to speed up the process. The matrix transforms the light reflection of the image into analog electrical signals (AES) .
• (AES) signals pass through an analog-to-digital converter. It converts an analog signal into digital form.
• The processor coordinates the interaction of all device nodes, including generating image data for subsequent sending to the PC.
• The interface controller controls the exchange of data and commands between the PC and the scanner.
• The lamp is installed on the scanning carriage.
• The stepper motor and control unit drive the carriage and the scanning head on it.

Operating principle

The scanner performs a scanning function to transfer a digital image to a PC or send by mail. For this purpose, the object is placed on the transparent glass of the device. When the unit is started, the carriage is set in motion and begins to glow. The optical system of the device, including a lens and mirrors, directs the light flux from the scanned surface of the object to the receiving element. It is where the data is converted.

The analog signal is sent to a converter where it is converted into digital code. Next, the controller comes into action, which transmits the code to the Personal Computer. On a PC, the resulting image can be edited and used for its intended purpose.

Application

The scanner is used in a wide variety of fields of activity:

• Companies and organizations where the device is used to scan documents.
• Printing.
• Photo studios.
• Industry.
• Libraries.
• Scientific laboratories.
• Schools, technical colleges and universities.
• In everyday life, and where there is a need to scan an image from a book, document, magazine, photograph, slide, and so on.

How to choose

The scanner should be selected taking into account where you intend to use it. It is necessary to decide what tasks it will perform. Unlike a computer, it will be difficult to upgrade a scanning device by installing additional components. Therefore, you should weigh the pros and cons.

• When choosing a scanner for home or office use, it is important to study it specifications. An office scanning device should best suit the specifics of the organization. In most cases, such technology in the office is used for scanning text documents and digitizing archives. Therefore, the device must have an automatic paper feed function.
• For organizations that work with large formats and printing, the ability to scan large-sized documents, as well as the quality of scanning, is important.
• For scanning at home, in most cases, they are guided by low price and compactness. For household use, there is no point in purchasing expensive equipment, because almost all scanning devices can cope with the tasks of an undemanding user. Not required here highest resolution, large format or interface that runs at high speed.
• The presence of a slide adapter in the device, including additional options such as red-eye removal or color restoration, will make use more convenient, especially if you want to scan photographs and negatives.
• Color depth determines how many shades of color the scanning device will perceive. For home use, 24 bits is sufficient.
• When purchasing directly, be sure to check the scanning device. To do this, you need to scan a photo or other document. You need to see how quickly the scanner works, how colors are transmitted, especially white. Scan clarity should be assessed the smallest details at a certain resolution, including what formats images can be saved in on a computer. If you are satisfied with everything, then you can safely make your purchase.

Lecture No. 7. Flatbed scanners

2. Flatbed scanners.

1.General characteristics of scanners

Each type of scanner has its own application characteristics, which leads to differences in scanning technology and, consequently, in the characteristics of the devices. However, there are some general criteria for evaluating both the scanner itself and the image obtained with it. Let's look at the general characteristics of scanning, regardless of specific types or models of scanners.

Scanner color. Like most other imaging devices, scanners are divided into

Colored;

Black and white (grayscale)

Line black and white.

Color scanners are the most common type.

Grayscale scanners “distinguish” between shades of gray, but are not capable of perceiving color images.

Line black-and-white scanners distinguish only two colors and are practically not represented in the retail chain - they are used mainly in various industries (for example, for scanning drawings or barcodes).

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

Optical resolution (opticalresolution) characterizes the minimum horizontal dot size that the scanner is able to recognize. In scanners that use a matrix to read color information (for example, flatbed or sheet-fed scanners), this characteristic is determined by the ratio of the number of elements in a matrix line to the width of the working area. For other types of scanners such as drum scanners, it is limited by the ability to focus light on the photoreceiving element. Optical resolution is always the smallest of all those specified for a particular scanner model, so scanner manufacturers often do not indicate it.

Mechanical resolution (mechanicalresolution) - the number of steps that the scanning carriage takes, divided by the length of the path it travels. Since information is read by the matrix at each step, this parameter determines the minimum vertical dot size that the scanner can recognize. Sometimes mechanical resolution is also called optical resolution, but this is incorrect. For example, if an optical resolution of 300x1200 ppi is specified for a scanner model, then the optical resolution will be 300 ppi, and the mechanical resolution will be 1200 ppi. Typically, the mechanical resolution is twice the optical resolution, but there are also models in which it is four times greater or, on the contrary, they are equal. Due to the fact that the CCD matrix cannot scan with a horizontal resolution greater than optical, mathematical interpolation methods are used to add missing points (otherwise the vertical size of any scanned square would be greater than the horizontal one). Mechanical resolution is only applicable to scanners with a matrix photodetector structure.

Interpolation resolution - resolution artificially increased using mathematical methods. The program included with the scanner tries to bring the image to this resolution by adding missing points (for example, with a real resolution of 3x3, the program produces 9x9). This parameter has nothing to do with the actual physical parameters of the scanner and can only characterize the image processing program.

Scanner resolution is usually measured in pixels per inch (ppi, pixel per inch). Measuring this parameter in dots per inch (dpi, dots par inch) is fundamentally incorrect, since dpi refers to the actual resolution of the printer, and this is a slightly different concept. Typically, a printer prints several dots to produce one color pixel, and each of them is responsible for its own color component. These points are very close, which creates the effect of one pixel of the desired color: they seem to merge. Accordingly, dpi refers to the number of dots per inch that make up a color. Ppi refers to the number of full-color pixels per inch.

Bit depth (color depth)- a parameter characterizing the number of colors or shades of gray (depending on the color of the scanner). Bit depth refers to how many bits the scanner uses to represent the color of a single point in an image. There are external and internal bit depths. Internal bit depth is the number of bits representing the point for internal operations in the scanner (that is, before the signal passes through the ADC and is converted to digital form). External bit depth determines the color bit depth after the signal passes through the ADC. The external bit depth of scanners is usually 8 bits (256 shades of gray) for grayscale scanners and 24 bits (8 bits per component, a total of 16.77 million colors) for color scanners. The internal bit depth is usually greater than the external one, not less. The extra bits in the internal bit depth (if any) are used to improve color accuracy and reduce the effect of distortion on color. |

Dynamic range- another color characteristic. The “quality” of light reflection from any original is expressed by optical density. It is calculated as the decimal logarithm of the ratio of the luminous flux incident on the original to the luminous flux reflected from the original (for opaque originals) or transmitted through it (for negatives or slides).

Optical Density is measured in OD (Optical Density), or simply D, and can range from 0.0D for perfect white (transparent) to 4.0D for perfect black (opaque).

Since we are talking about a logarithm, for example, 2.0D and 3.0D will differ not by 25%, but by 10 times. Optical densities for some types of originals are given in table. 1.

Table 1. Optical densities of some originals

Original

Optical Density Range

Newsprint

Coated paper

Photographs

Negative films

Commercial quality color slides

High quality transparencies, film and double slides

The range of optical densities of the scanner indicates which of the colors of the original will still be recognized and which will no longer be recognized, that is, they will be perceived as either completely white or completely black. The range of optical densities includes two characteristics: D min and D max. The first, D min, is the optical density of the original, below which the scanner will consider the original perfectly white. Accordingly, D max is the optical density of the original, above which the scanner will consider the original completely black. The range itself is the difference between D min and D max. The range of optical densities of the scanner depends on the quality and bit capacity of the ADC and photocells, as well as on the operating algorithm of the scanner controller. In table 2 shows typical dynamic ranges for common types of scanners.

Table 2. Typical dynamic ranges of scanners

Type, scanner class

Typical dynamic range

Handheld scanners

Grayscale scanners

Color flatbed scanners, old and SOHO class models

Intermediate color flatbed scanners

High-end color flatbed scanners

Tabletop Drum Scanners

High-end drum scanners

Working area of ​​the scanner-the maximum document format that the scanner is able to process. The format depends on the design and application of the scanner. Thus, the document format for sheet-fed and hand-held scanners is limited only in width. Conventional home and office scanners most often correspond to A4 formats and the Legal format accepted in the West. Professional models can have fixed sizes tailored to specific originals (for example, a 35mm film slide scanner), or simply have a large format - up to AO.

Scan speed- a parameter that reflects the time during which a particular document will be scanned. In fact, this characteristic cannot have any significance, since it depends on the speed of the computer, the volume of its random access memory, from the hardware interface, etc. Therefore, the performance of the scanner can only be assessed for a specific workplace. Sometimes this parameter is indicated in the scanner characteristics in milliseconds per line.

Scanner hardware interface(data interface) provides information exchange between the scanner and the computer. The speed of data transfer between the computer and the scanner depends on it. This characteristic can be very important if there is a need for high quality scanned photographs (or any other graphic materials). For example, a standard 10 x 15 cm color photograph scanned at 720 ppi at 24-bit True color will require about 40 MB of disk space. Accordingly, if the data transfer speed between the scanner and the computer is low, then you will have to wait a very long time for the result. Therefore, the data transfer interface is placed on a par with such characteristics as resolution and color depth. Currently, there are scanners with five types of interfaces on the market:

1. Interface LPT (standard parallel port Centronics). This interface is one of the slowest, but also the easiest to install a scanner: Sometimes there are improved options - with support (or even a requirement) for EPP/ECP. In this case, installation problems may arise, since not all computers are equipped with such ports. Scanners with an LPT interface almost always have a “pass-through port,” that is, the scanner does not exclusively use the LPT port, leaving the possibility of connecting another device (usually this device is a printer).

2. Own interface. It is also sometimes called ISA. This interface is implemented in the form of a separate card with which the scanner can work. Such cards are unique for each scanner model, which can cause problems during replacement (if the card, for example, fails) or after Upgrade.

3. SCSI interface - one of the fastest data transfer interface options. However, if a SCSI card is not supplied with the scanner, then compatibility issues with other SCSI controllers may arise. Adaptec controllers create the least problems. If the scanner comes with its own card, then connecting and using the scanner will not cause problems, but it is not a fact that other SCSI devices can be installed on this controller (for example, due to the lack or incompatibility of drivers). When connecting a scanner to a SCSI card, bus matching must be observed, otherwise the devices connected to it will not be able to operate normally. The beginning and end of the device chain must be provided with terminators (matching resistances). If there are no external devices, then the terminator can be installed directly on the controller, which serves as the last link in the SCSI chain. Since the scanner is best installed last in the chain, you must enable the scanner's own terminator by disabling the controller terminator. Most scanners have terminators inside. Only a few scanners (eg HP ScanJet 4p) have an external switch.

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

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

2. Flatbed scanners

Flatbed scanners are the most common type of scanner. This popularity is well deserved: the design of such scanners creates all the convenience when scanning any originals. The original in a flatbed scanner lies motionless on the glass, and reading in most cases occurs in light reflected from it. The high speed characteristics of such scanners are also a definite advantage. This advantage is achieved due to the fact that the photocell in flatbed scanners is not a single photocell, but a reading line of photocells.

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

In Fig. Figure 1 shows a diagram of the flatbed scanner device. A stripe of light emitted by a light source hits the original stretched on the glass. After being reflected, the light hits the first mirror of the mirror system. The mirrors are positioned so that the reflected light hits the collecting lens. The lens projects the light that hits it onto a line of photocells (with magnification). The light that hits this line is transformed into an electrical analog signal, which then enters the ADC. In some scanners, between the photodetector and the ADC there are intermediate stages that work with an analog signal. These stages are designed to hardware correct scanning errors and, sometimes, the image itself. As a result, a strip of the image of the original original goes to the output, that is, to the computer (after the ADC).

The scanning procedure described above covers only one line of the image. Therefore, the head is used for a full scan. Once the scanned string of pixels enters the computer, the carriage moves one step. The length of this step is fixed and the mechanical resolution of the scanner depends on it (see the section “General characteristics of scanners”). Then the entire procedure is repeated until the specified area has been read completely. Let's take a closer look at the described scanner parts.

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

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

3. Photoreceiving matrix This and the following parts in the list are located on the so-called scanning head or carriage). This is practically the most essential part of the scanner. Optical resolution, dynamic range, scanner operation scheme (one-pass or three-pass) and almost all other characteristics (except perhaps the scanner’s working area) depend on it. Today, two types of photoreceiving matrix are most common:

CCD matrices (charge-coupled device, in English notation - CCD, Couple-Charged Device);

CDI matrices (contact image sensor, in English notation - CIS, Contact Image Sensor).

The basis of the CCD matrix element is a phototransistor made using MOS (metal-oxide-semiconductor) technology. This technology is used in many other image reading devices, from the most powerful telescopes to night vision devices.

This type of photocells has its own advantages and disadvantages. Among the advantages of CCD, the following should be noted:

High sensitivity. The quantum efficiency of CCDs is extremely high and can reach 95%. For comparison, the quantum efficiency of the human eye is about 1%, the best photo emulsions have a quantum efficiency of up to 3%, photomultiplier tubes (photodetectors in drum scanners) - up to 20%. Quantum efficiency determines the ability of a photodetector to convert light into electrical signals, that is, it expresses the efficiency of converting quanta (light particles) that hit it into an electrical signal. Strictly speaking, it is equal to the ratio of the number of registered charges to the number of photons striking the photosensitive region of the CCD crystal. The quantum energy depends on the wavelength of the light, so it is impossible to clearly define this characteristic for a CCD - it varies across the entire spectrum and is usually specified as a function of the wavelength.

Wide spectral range. A CCD can respond to light ranging from gamma and x-rays to infrared radiation. None of the matrix technologies currently provides such a range. The main disadvantages of CCD are:.

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

Noises. There are several types of noise. Some types of noise depend on temperature, so high-quality CCDs sometimes use cooling. Other types of noise depend on the build quality of the CCD. But there is also noise that cannot be filtered out even in the highest quality devices. For example, such noise is photon noise. This noise is a consequence of the nature of light and does not depend on the photodetector. All these noises introduce corresponding distortions into the scanning result. Typically, distortion appears as noise bits. In low-end scanners, for each of the three color components (8 bits each), the two most significant bits are “noise” and do not contain accurate color information.

Charge spreading. This effect occurs because the charge stored in the CCD element varies linearly depending on the light that hits it. Accordingly, there is a certain limit limiting this charge. If during illumination the total number of photons (light particles) exceeds the limit value, then the charge will begin to “flow” into neighboring pixels. In the resulting image, this appears as a blurring of too-bright details in the image.

There is no fundamental difference between CD I and CCD matrices. CDI scanners differ from CCD scanners in that the matrix in them is stretched across the entire width of the working area, so there is no optical system at all.

However, the design of many other components depends on the technology of the photoreceiving matrix, so we should not talk about differences in the scanning matrix, but about differences in scanners.

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