Optical-electronic scanning method. Moscow State University of Printing. Optical-mechanical scanning systems
SCANNING OPTICAL - ELECTRONIC IMAGING SYSTEMS (SCANERS)
Scanning filming systems (scanners) differ from others primarily in the principle of image construction, which is constructed by line-by-line scanning (viewing) of the area.
Scanning systems use various types of electromagnetic radiation receivers: thermal (thermoelectric) and photonic (photoelectric). Thermal ones operate on the basis of converting thermal energy into an electrical signal; in photonic systems, the signal level is determined by the number of absorbed photons. The most widely used are scanners in which CCD lines (devices with a charge mixture) serve as receivers. Different types of sensors have different spectral sensitivities and cover the spectral range from the visible zone to the far infrared zone. The choice of radiation receiver and its spectral sensitivity depends on the spectral interval of the survey.
Structurally, the scanner consists of an optical system, photoelectronic converters, and an image receiving and recording device. With the help of scanners, an image is formed consisting of many individual, sequentially obtained image elements - pixels within stripes (lines, scans). Pixel size determines the detail (terrain resolution) of the image.
Scanning of the area is carried out in one direction due to the forward movement of the aircraft (satellite), and in the other (perpendicular to the flight line) due to the rotation or oscillation of the prism (mirror). The oscillatory movement of the prism (mirror) in combination with the movement of the aircraft (satellite) provides continuous sequential coverage of a certain strip of terrain, the size of which depends on the aperture (the actual opening of the optical system of the lens) of the scanner and the flight altitude of the aircraft or satellite. The width of the strip of terrain being photographed is determined by the scanning angle of the scanner, and the linear resolution of the terrain (scan width, pixel size) is determined by the instantaneous viewing angle. For overview scanners, the scanning angle reaches, while for highly informative (detailed) scanners, it is less. Accordingly, the instantaneous angle of view is set from several degrees to tenths of a minute. The scanning angle and instantaneous viewing angle, respectively, the shooting range and terrain resolution, are interdependent quantities. The higher the resolution, the narrower the shooting band. So, when shooting from space at a resolution of 1-2 km. They record a strip of terrain of several thousand kilometers, and with a resolution of 20-50 m, the width of the survey strip does not exceed 100-200 km.
Optical-mechanical scanners can be single-channel or multi-channel (2 or more). Typically, scanners operating in the visible and IR ranges (0.5 - 12 microns) are used to photograph the earth's surface. The result of radiation registration when shooting using the optical-mechanical scanning method is a matrix of multidimensional vectors. Each vector displays a certain elementary area (pixel) on Earth, and each of its components corresponds to one of the spectral channels.
When shooting in the visible and near-IR ranges (0.4 - 3 microns), photoelectric radiation detectors are used, and in the middle and far-IR ranges (3 -12 microns) - thermoelectric radiation detectors. Photoelectric receivers include electronic devices whose operation is based on external (vacuum photocells, photomultipliers) and internal (semiconductor photoresistors, photodiodes, etc.) photoelectric effects. Thermoelectric detectors are based on thermionic emission; they respond to absorbed radiation through heating the sensitive element, which makes it possible to record IR thermal radiation in a wide spectral range. Thermoelectric receivers include bolometers, radiation thermoelements (thermocouples), etc. Thermal imaging is carried out by scanning radiometers at night and during the day.
Scanners are equipped with several sensors that allow them to obtain images simultaneously in different spectral channels. The information obtained during the scanning process is transmitted in the form of a digital image via a radio channel to a receiving point or recorded on board on a magnetic medium. The shooting materials are transferred to consumers in the form of recordings on magnetic media, for example, on CDs, with subsequent visualization at the image processing sites.
In terms of their geometric properties and local resolution, scanner images obtained by first-generation camera systems were inferior to photographs. However, the high sensitivity of the scanners' radiation detectors allows them to perform shooting in narrow (several tens of nanometers) spectral intervals, within which the differences between some natural objects are more clearly expressed. There is no “noise” in the digital data obtained using scanners, which inevitably appears when photographing and darkroom processing of film materials.
Scanning systems appeared in the mid-70s and by the end of the 80s almost completely replaced traditional photographic and television systems. Today they are the main suppliers of remote sensing data when solving problems of natural resource and environmental monitoring.
In general terms, the scanning mechanism is as follows. The satellite has a scanner equipped with a photoelectric or thermoelectric receiver. This receiver receives reflected radiation from a certain area of the earth's surface. The receiver generates an electrical signal depending on the intensity of the radiation. The magnitude of the signal is recorded in the device’s memory, and the sensor begins to receive the signal from the next section of the earth’s surface. Thus, section by section, an image begins to form. Each such section of the earth's surface, the reflection from which was simultaneously recorded by the sensor, is displayed in the image as a pixel - the smallest indivisible element of the image. Each pixel reflects the average brightness value of all objects falling within the boundaries of a given pixel. Thus, the smaller the pixel size, the better the image can be obtained in the image, since it becomes possible to display smaller objects.
There are two types of remote sensing scanner systems − optical-mechanical (divided into linear and transverse) and optical-electronic (longitudinal and planar).
IN line scanners(a single detector element is used to capture the entire scene
Figure 1 – Linear optical-mechanical scanner
Scanners of this type have a mirror installed that swings from side to side across the direction of the satellite's movement. The mirror is sequentially hit by reflected radiation from different parts of the surface along the line, and from the mirror it already hits the detector. Having reached the extreme point of the line, the mirror begins to rotate in the opposite direction, reading the next line (during this time the satellite has flown a distance corresponding to one line of pixels). Thus, line by line the image is built up. The oscillation of the mirror across the shooting route realizes the lines of the image, and thanks to the movement of the carrier, the lines accumulate and a complete image of the image is formed, which has a line-mesh element-by-element structure.
Another type of linear scanner is a scanner in which the mirror does not swing from side to side, but always rotates in one direction around its axis, in a range of 360 degrees. Here the sensor reads the signal along the line, and then, while the sensor is moving around its axis, the satellite moves some distance forward and the sensor again begins to read the next line in the same direction. About 7 such cycles are carried out in one second.
IN cross-sectional CCD scanners, for example, the TM (Thematic Mapper) scanner of the Landsat-5 satellite uses a line of detectors located along the survey route. Such a line is called a CCD line (charge-coupled device; the name reflects the method of reading the electric potential by shifting the charge from element to element). As a result, with each cycle of movement of the mirror, all detector elements carry out parallel scanning of the earth's surface. As with line scanners, the sensor's movement can be from side to side as the next line is read in the opposite direction, or around its own axis.
The main disadvantage of devices of this type is the presence of a mechanical scanning mirror, which limits the accuracy of the geographic location of the resulting images and reduces the durability and reliability of the device as a whole. In optoelectronic charge-coupled device (CCD) cameras, called “push-broom scanners,” mechanical scanning elements are not used. An image line in one spectral range is formed using a linear array (line) of CCD detectors oriented perpendicular to the direction of flight of the satellite.
Longitudinal CCD scanners equipped with a CCD array consisting of thousands of detector elements located across the route. As a result, parallel scanning of the entire data set occurs simply due to the movement of the platform in orbit.
Planar CCD is a matrix of sensors, similar to the matrix in a conventional digital camera. It is necessary to ensure sufficient time for a certain number of photons to reach the sensor. If the sensor is in motion relative to the target, incremental imaging is applied to prevent blurring.
Regardless of the type of scanning system, the full scanning angle across the survey route is called viewing angle, and the corresponding value on the Earth’s surface shooting bandwidth(another name is coverage bandwidth ). The distance on the earth's surface corresponding to the distance between the centers of adjacent pixels is called ground sampling interval (another name is ground scan step ). Ground sampling intervals along and across the survey route are determined by the corresponding sampling rates, as well as the speed of the platform. In practice, the sampling frequency is usually selected so that the value of the ground sampling interval is equal to the size of the instantaneous field of view, that is, the width of the projection of one detector element onto the earth's surface (Fig. 2 and 3). Thus, the instantaneous fields of view of neighboring pixels are adjacent to each other in both the longitudinal and transverse directions. The ground sampling interval along the survey route is determined by the platform speed and either the sampling rate (for longitudinal CCD scanners) or the scan rate (for linear and transverse CCD scanners), which are adjusted to match the instantaneous field of view at nadir. The use of higher lateral sampling rates in some systems results in overlapping instantaneous fields of view and, as a result, some improvement in data quality. This “redundant scanning” method is used, in particular, in the Landsat MSS and AVHRR KLM survey systems.
Figure 2 – The simplest geometric diagram of the location of the detector element in the focal plane of the sensor
Figure 3 – Relationship between instantaneous field of view projection and sampling interval for typical scanners and for MSS and AVHRR instruments
The ground GSI sampling interval is determined by the height of the platform H, the focal length f and the interdetector interval (or, as noted above, the spatial sampling frequency). If the sampling rate is one pixel per detector interval, the ground interval at nadir, that is, directly under the sensor, is given by a simple formula:
Where m = f/H is the coefficient of geometric magnification, and the value of the interdetector interval is usually equal to the width of the detector element w.
The instantaneous field of view of GIFOV depends on the values of H, f, and w in a similar manner. It should be noted that engineers developing remote sensing systems prefer to use another parameter in their calculations - the value of the instantaneous viewing angle IFOV, equal to the angle formed by the detector element with the axis of the optical system (Figure 2). This is due to the fact that IFOV is a constant value and does not depend on the operating height of the sensor.
Data obtained from optical sensors with high spatial resolution are used in solving a wide range of thematic problems, including, for example, measuring the extent and classification of vegetation cover, determining the health of crops, geological mapping, monitoring soil erosion in the coastal zone, etc. However, the scope of applicability of these data is somewhat limited by the fact that obtaining high-quality optical images is possible only on the illuminated part of the Earth's surface in clear, cloudless weather.
For office and home tasks, as well as for most computer graphics work, the so-called flatbed scanners. Various models of this type are more widely available on sale than others. Therefore, let's start by considering the principles of construction and operation of scanners of this particular type. Understanding these principles will provide a better understanding of the technical characteristics that go into choosing scanners.
A flatbed scanner is a rectangular plastic case with a lid. Under the cover there is a glass surface on which the original is placed to be scanned. Through this glass you can see some of the insides of the scanner. The scanner has a movable carriage on which a backlight lamp and a mirror system are installed. The carriage moves through the so-called stepper motor. The lamp light is reflected from the original and, through a system of mirrors and focusing lenses, enters the so-called matrix, consisting of sensors that produce electrical signals, the magnitude of which is determined by the intensity of the light incident on them. These sensors are based on light-sensitive elements called charge coupled devices(CCD, Couple Charged Device - CCD). More precisely, an electrical charge is generated on the surface of the CCD that is proportional to the intensity of the incident light. Next, you only need to convert the magnitude of this charge into another electrical quantity - voltage. Several CCDs are located side by side on one line.
The electrical signal at the output of the CCD is an analog quantity (i.e., its change is similar to the change in the input quantity - light intensity). Next, the analog signal is converted into digital form, followed by processing and transmission to a computer for further use. This function is performed by a special device called analog-to-digital converter(ADC, Analog-to-digital Converter - ADC). Thus, at each step of moving the carriage, the scanner reads one horizontal strip of the original, divided into discrete elements (pixels), the number of which is equal to the number of CCDs on the line. The entire scanned image consists of several such stripes.
Rice. 119. Diagram of the design and operation of a flatbed scanner based on a CCD (CCD): the lamp light is reflected from the original and, through an optical system, hits a matrix of photosensitive elements, and then to an analog-to-digital converter (ADC)
Color scanners now typically use a three-row CCD matrix and illuminate the original with calibrated white light. Each row of the matrix is designed to perceive one of the basic color components of light (red, green and blue). To separate colors, they use either a prism, which splits a beam of white light into colored components, or a special CCD filter coating. However, there are color scanners with a single-row CCD matrix, in which the original is illuminated in turn by three lamps of basic colors. Single-row, triple-illuminated technology is considered obsolete.
Above we described the principles of construction and operation of so-called single-pass scanners, which scan the original in one carriage pass. However, three-pass scanners are still found, although no longer commercially available. These are scanners with a single-row CCD matrix. In them, with each pass of the carriage along the original, one of the basic color filters is used: for each pass, information is removed from one of the three color channels of the image. This technology is also outdated.
In addition to CCD scanners based on a CCD matrix, there are CIS (Contact Image Sensor) scanners that use photocell technology.
Photosensitive matrices made using this technology perceive the reflected original image directly through the scanner glass without the use of optical focusing systems. This made it possible to reduce the size and weight of flatbed scanners by more than half (down to 3-4 kg). However, such scanners are only good for extremely flat originals that fit tightly to the glass surface of the working field. In this case, the quality of the resulting image significantly depends on the presence of extraneous light sources (the CIS scanner cover must be closed during scanning). In the case of volumetric originals, the quality leaves much to be desired, while CCO scanners give good results for volumetric (up to several cm in depth) objects.
Flatbed scanners can be equipped with additional devices, such as a slide adapter, automatic document feeder, etc. Some models are provided with these devices, but others are not.
Slide adapter (Transparency Media Adapter, TMA) is a special attachment that allows you to scan transparent originals. Transparent materials are scanned using transmitted rather than reflected light. In other words, the transparent original must be between the light source and the photosensitive elements. The slide adapter is a mounted module equipped with a lamp that moves synchronously with the scanner carriage. Sometimes they simply illuminate a certain area of the working field evenly so as not to move the lamp. Thus, the main purpose of using a slide adapter is to change the position of the light source.
If you have a digital camera (digital camera), then you most likely do not need a slide adapter.
If you scan transparent originals without using a slide adapter, you need to understand that when the original is irradiated, the amounts of reflected and transmitted light are not equal to each other. So, the original will miss some of the incident color, which will then be reflected from the white coating of the scanner lid and pass through the original again. Some of the light will be reflected from the original. The ratio between the parts of transmitted and reflected light depends on the degree of transparency of the original area. Thus, the light-sensitive elements of the scanner matrix will receive light that has passed through the original twice, as well as light reflected from the original. The repeated passage of light through the original weakens it, and the interaction of the reflected and transmitted beams of light (interference) causes distortion and side video effects.
An automatic document feeder is a device that feeds originals into the scanner, which is very convenient to use when streaming images of the same type (when you do not need to frequently reconfigure the scanner), for example, texts or drawings of approximately the same quality.
In addition to flatbed ones, there are other types of scanners: manual, sheet-fed, drum, slide, for scanning barcodes, high-speed for streaming documents.
Handheld Scanner is a portable scanner in which scanning is carried out by manually moving it over the original. The principle of operation of such a scanner is similar to that of a tablet scanner. The width of the scanning area is no more than 15 cm. The first scanners for widespread use went on sale in the 80s of the 20th century. They were manual and allowed scanning of images in shades of gray. Nowadays such scanners are not easy to find.
Sheet or roller scanner(Sheetfed Scanner) - a scanner in which the original is pulled past a stationary linear CCD or CIS matrix; a type of such a scanner is a fax machine.
Drum scanner(Drum Scanner) - a scanner in which the original is fixed on a rotating drum, and photomultipliers are used for scanning. In this case, a dot area of the image is scanned, and the scanning head moves along the drum very close to the original.
Slide scanner(Film-scanner) is a type of flatbed scanner designed for scanning transparent materials (slides, negative films, X-rays, etc.). Usually the size of such originals is fixed. Note that some flatbed scanners have a special attachment (slide adapter) designed for scanning transparent materials (see above).
Barcode scanner(Bar-code Scanner) - a scanner designed for scanning product barcodes. According to the principle of operation, it is similar to a hand-held scanner and is connected to a computer or to a specialized trading system. If you have the appropriate software, any scanner can recognize barcodes.
High-speed scanner for working with documents(Document Scanner) is a type of sheet-fed scanner designed for high-performance multi-page input. Scanners can be equipped with input and output trays with a capacity of over 1000 sheets and input information at speeds in excess of 100 sheets per minute. Some models of this class provide two-sided (duplex) scanning, backlighting the original in different colors to cut out the colored background, compensation for background heterogeneity, and have modules for dynamic processing of different types of originals.
So, a flatbed scanner is best for home and office use. If you want to do graphic design, then it is better to choose a CCD scanner (based on a CCD matrix), since it allows you to scan three-dimensional objects. If you plan to scan slides and other transparent materials, you should choose a scanner that has a slide adapter. Usually the scanner itself and the slide adapter that goes with it are sold separately. If you cannot purchase a slide adapter at the same time as the scanner, you can do so later if necessary. It is also necessary to determine the maximum sizes of scanned images. Currently, the standard format is A4, corresponding to a regular sheet of writing paper. Most household scanners are designed specifically for this format. Scanning drawings and other design documents typically requires A3 size, which corresponds to two A4 sheets joined along the long side. Currently, the prices of scanners of the same type for A4 and A3 formats are getting closer. It can be assumed that originals that do not exceed the A4 format will be better processed by a scanner oriented to the A3 format.
The parameters listed above do not exhaust the entire list, but at this stage of our consideration we can only use them for now. When choosing a scanner, three aspects are decisive: a hardware interface(connection method), optical-electronic system And software interface c (the so-called TWAIN module). Next we will look at them in more detail.
The main method of converting paper documents into electronic form is scanning graphic image scanner.
Scanner
universal And special.
Universal scanners provide input of text and graphic information in color or black and white format. Among the universal scanners, the following types stand out:
· Hand scanner– the simplest type of scanners, which gives the least quality image. This type of scanner has no moving parts and scanning is done by manually moving the scanner over the surface of the document. Their disadvantage is a very narrow scanning bandwidth (a standard sheet of paper has to be scanned in several passes), as well as high requirements for the scanning process itself.
· Sheet-fed scanner– allows you to scan a standard size sheet of paper in one operation. The design is similar to a fax machine: the original is pulled in by special rollers (like in a printer) and scanned as it moves past a stationary photosensitive matrix. While providing high quality scanning, these scanners do not allow you to process books and magazines without separating them into separate pages.
· Flatbed scanner– the most universal device, suitable for most tasks and allowing you to scan any documents (single sheets, books, magazines, etc.). Under the scanner cover there is a transparent base on which the document is placed. The scanning unit moves along the document inside the scanner body. The duration of scanning a standard typewritten sheet ranges from one to several seconds. Flatbed scanners provide the best quality and maximum convenience when working with paper documents.
Many models of flatbed scanners have the ability to install an automatic document loader from a stack, as well as connect a slide module that “digitizes” slides and negative films for professional photography or printing tasks.
Special types of scanners are designed to perform special functions. These include the following:
· Drum scanners provide the highest scanning resolution. The original is fixed to the drum using special clamps or lubricant, and scanning is carried out by line-by-line movement of the lens along the drum rotating at a speed of about 1000 revolutions per minute. The use of a halogen light source, the luminous flux from which is concentrated on a pinpoint area of the drum, eliminates the influence of interference and processes the entire range of originals with the highest quality.
· Form scanners - special scanners for entering information from completed forms. This is a type of sheet-fed scanner. Using such devices, data is entered from questionnaires, questionnaires, and ballot papers. Scanners of this type do not require high resolution, but very high performance. In particular, for scanners of this type, the feeding of paper sheets into the device is automated.
· Bar scanners - a type of hand-held scanners designed to read 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, smart cards, etc.).
· Slide scanner- a specialized version of a flatbed scanner designed for digitizing slides and negative films for professional photography or printing tasks. The slide or film is inserted into the receiving slot and moves between the backlight and the lens. The parameters of the output image are sufficient for a photo album or printing reproduction.
Despite such a variety of types of scanners, the design and principles of their operation are largely similar. As an example, let's look at how a flatbed scanner works, a simplified block diagram of which is shown in Fig. 10.
The main elements of a flatbed scanner are:
· substrate(cover) – covers the original from which scanning is performed. It is made of black material that absorbs the visible part of the spectrum as much as possible in order to prevent the appearance on the resulting image of all kinds of glare of light reflected from objects placed behind the original;
·
glass, on which the scanned original is placed;
· LED matrix– a set of sensors (photosensitive elements) arranged in one line for black and white scanning or in three lines for color scanning in one pass. Charge-coupled devices are used as photosensitive elements ( CCD – CCD –Charge Coupled Device). The main purpose of the matrix CCD– divide the luminous flux into three components (red, green and blue) and convert the light level into a voltage level;
· optical system– consists of a lens and mirrors (or prism) and is designed to project the light flux reflected from the scanned original onto an LED matrix that separates color information. Typically a single focusing objective (or lens) is used that projects the full width of the scanning area onto the full width of the CCD;
· lamp– a light source located on a moving carriage and illuminating the page being scanned. Modern models use cold cathode lamps ( Cold Cathode Lamp), providing a luminous flux of a given intensity and having increased durability characteristics. Focused on professional work with color, the scanners contain self-calibration circuits based on the intensity of the light flux from the lamp and maintaining the stability of the light flux when temperature changes;
· stepper motor– provides movement optical block, which includes a lamp, optical system and LED matrix;
· signal amplification unit– amplifies analog voltages from the outputs of the CCD matrix, carries out their correction and processing;
· analog-to-digital converter (ADC) – converts analog voltages into digital code;
· scanner controller– ensures the reception of commands from the computer and the issuance of received digital codes to it.
The scanning process is quite simple. The original (sheet of document, unfolded book, etc.) is placed on transparent fixed glass and covered with a lid. When a scanning command is sent from the computer, the lamp turns on and the scanning carriage with the optical unit begins to move along the sheet. Bright light from the lamp falls on the scanned original, and then, reflecting from it, the light flux is focused by the optical system and enters the signal receiver - a CCD matrix, which separately perceives the red, green and blue components of the spectrum. The analog voltages obtained at the output of the CCD matrix, proportional to the spectral components, are amplified and fed to an analog-to-digital converter, which performs digital encoding. From the ADC, information comes out in a binary form “familiar” to the computer and, after processing in the scanner controller, through the interface with the computer it enters the scanner driver - usually the so-called TWAIN- a module with which application programs already interact.
! To see how a flatbed scanner works, put on headphones and double-click on this picture:
Main parameters and characteristics of scanners:
1. Scan Resolution (Scanning Resolution) characterizes the magnitude of the smallest image details transmitted during scanning without distortion. Usually measured in dpi (dot per inch) - the number of individually visible dots per inch of the image. There are several types of resolution specified by the scanner manufacturer.
· Optical resolution is determined by the density of elements in the CCD array and is equal to the number of elements in the CCD array divided by its width. It is the most important parameter of the scanner, determining the detail of the images obtained with its help. In mass models of flatbed scanners it is usually equal to 600 or 1200 dpi. Scanning should always be performed at a multiple of optical resolution to ensure minimal interpolation distortion.
· Mechanical resolution determines the positioning accuracy of the carriage with the CCD ruler when moving along the image. Mechanical resolution is usually 2 times greater than optical resolution.
· Interpolation resolution obtained by 16x software magnification of the image. It carries absolutely no additional information about the image compared to the real resolution, and in specialized packages the scaling and interpolation operation is often performed better than by a scanner driver.
2. color depth, or bit depth (Color Depth) characterizes the number of bits used to store information about the color of each pixel. Black and white scanners have one bit, monochrome scanners usually have 8 bits, and color scanners have at least 24 bits (8 bits to store each of the RGB color components of a pixel). The number of colors reproduced by a 24-bit scanner (8 bits per channel) is 2 24 = 16,777,216. More advanced scanners may have a bit depth of 30 or 36 (10 or 12 bits per channel). Moreover, their internal bit depth may be higher than the external one: “extra” bits are used to perform color correction of the image before transferring it to a computer, although this practice is mainly typical for cheap models. Professional and semi-professional scanners also have external bit depths of 30, 36, 42 bits or higher.
3. Optical Density Range (Optical Density Range) is the dynamic range of the scanner, which is largely determined by its bit depth. It characterizes the scanner’s ability to correctly transmit images with large or very small variations in brightness (the ability to scan “a photo of a black cat in a dark room”). Calculated as the decimal logarithm of the ratio of the intensity of the light incident on the original to the intensity of the reflected light, and is measured in OD(Optical Density) or simply D: 0.0 D corresponds to perfect white, 4.0 D corresponds to perfect black. For a scanner, this range depends on the bit depth: for a 36-bit scanner it does not exceed 3.6 D, for a 30-bit scanner - 3.0 D. Scanned images usually have a range of up to 2.5 D for photographs and 3.5 D for slides . Cheap 24-bit flatbed scanners have a dynamic range of 1.8-2.3 D, good 36-bit ones - up to 3.1-3.4 D.
4. Scan area size. For flatbed scanners, the most common formats are A4 and A3, for roll scanners - A4, and for hand-held scanners, the scanning area is usually a strip 11 cm wide.
5. Matching the colors of the original image to its digital copy. Today, one of the most common color accuracy management systems is that based on profiles. International Color Consortium (ICC), describing the color rendering features of various devices. The process of creating an ICC profile is based on scanning a specially made test table and comparing the results obtained with the standard. Based on the results, the device characteristics that are taken into account by the driver and applications are determined. Expensive scanner models use special software and hardware systems for color calibration.
6. Driver quality. All modern scanners communicate with Windows applications using a software interface TWAIN, however, the set of functions provided by the driver may vary; it should definitely be clarified when choosing a scanner. The most important among them are:
· the ability to preview an image with a choice of scanning area and number of colors;
· ability to adjust brightness, contrast and non-linear color correction;
· the ability to suppress moire when scanning images with a printed raster;
· the possibility of simple image transformations (inversion, rotation, etc.);
· network scanning capability;
· possibility of automatic correction of contrast and color rendering modes;
· the ability to operate the scanner (in combination with a printer) in copier mode;
· color calibration capabilities for both the scanner and the entire system;
· Batch scanning capabilities;
· the ability to fine-tune filters and color correction parameters.
7. Quantity and quality of software included with the scanner. Traditionally, image processing software is supplied with scanners ( Adobe PhotoDeluxe or Photoshop LE, ULead Photo Impact etc.) and an optical text recognition program ( OCR - Optical Character Recognition). The software package usually includes two such programs: English ( Xerox TextBridge or Caere OmniPage Pro) and an OCR program designed to recognize Russian texts - one of the versions FineReader production ABBY Software.
High-quality professional and semi-professional flatbed scanners are produced by companies Agfa, Linotype-Hell, Microtek(a number of models are known under the NeuHouse OEM logo), Umax; Equipment designed for mass users is produced by companies Artec, Epson, Genius, Hewlett-Packard, Mustek, Plustek, Primax etc.
For various types of scanners in table. 3 shows typical values of these parameters.
Table 3. Parameter values for the main types of scanners
The following interfaces are currently used to connect scanners:
· own (Proprietary) scanner developer interface, used in early models of flatbed and hand-held scanners and was a specialized board on a bus ISA, which required a driver to operate;
· With EPP parallel port (LPT, or ECP) the youngest models are produced in families of flatbed scanners from various manufacturers. Scanners with such an interface, as a rule, have mediocre characteristics and are designed to perform simple work;
· SCSI interface is a standard for connecting high-quality and high-performance devices, ensures cross-platform compatibility of the scanner and its low dependence on changing the operating system. SCSI scanners usually come with a SCSI bus card ISA, although such a scanner can also be connected to full-featured SCSI controllers on the bus PCI. Most 30- and 36-bit scanners with a resolution of 600 dpi and higher are available with this interface;
· USB interface is an interface for connecting scanners, actively recommended by the specifications PC98 And PC99. The convenience of a single interface for different devices and fairly high throughput have led to the fact that most scanners for non-professional use are produced with this interface.
For data entry in three-dimensional modeling and computer-aided design systems (CAD, or CAD/CAM - Computer-Aided Design/Modeling) is used graphics tablet (Digitizer – digitizer)- an encoding device that allows you to enter a two-dimensional, including multicolor, image into a computer in the form of a raster image.
The graphics tablet includes a special pointer (pen) with a sensor. Its own controller sends impulses along a grid of conductors located under the surface of the tablet. Having received two such signals, the controller converts them into coordinates transmitted to the PC. The computer translates this information into coordinates of a point on the monitor screen corresponding to the position of the pointer on the tablet. Drawing tablets are sensitive to pen pressure, converting this data into line thickness or shade.
A serial port is usually used to connect a tablet. Common parameters are a resolution of about 2400 dpi and high sensitivity to pressure levels (256 levels). Graphic tablets and digitizers are produced by companies CalComp, Mutoh, Wacom and others.
For handwritten information input devices, the same operating scheme is typical, only the entered letter images are additionally converted into letters using a special recognition program, and the size of the input area is smaller. Pen input devices are more often used in subminiature computers PDA (Personal Digital Assistant) or HPC (Handheld PC), which do not have a full keyboard.
CONCLUSIONS
1. Keyboard is the main device for inputting information into a PC. It is a set of mechanical sensors that sense pressure on the keys and close a certain electrical circuit. The two most common types of keyboards are: mechanical and with membrane switches.
All keys are divided into groups: alphanumeric keys, intended for entering texts and numbers; cursor keys(this group of keys can also be used to enter numeric data, view and edit text on the screen); special control keys(switching registers, interrupting program operation, printing screen contents, rebooting the PC OS, etc.); function keys, widely used in utility programs as control keys.
The most common standard for symbol key layout is the layout QWERTY (YTSUKEN), which can be reprogrammed to another if desired.
2. A convenient tool for controlling the cursor is a device called mouse. The vast majority of computer mice use optical-mechanical principle of displacement coding. In laptop PCs, a trackball, touchpad, and trackpoint are used instead of a mouse.
3. Used to visually display information video system computer, including monitor(display), video adapter And software(video system drivers). Monitor (display) is a device for visually displaying text and graphic information on a kinescope screen (cathode ray tube - CRT) or liquid crystal screen (LCD screen).
TO basic parameters of monitors include: monitor frame rate, line frequency, video signal bandwidth, image formation method, monitor screen phosphor grain size, monitor resolution, monitor screen size.
Video adapter(video card, video controller) is an internal PC device designed to store video information and display it on the monitor screen. It directly controls the monitor, as well as the process of displaying information on the screen by changing the horizontal and vertical scanning signals of the CRT monitor, the brightness of image elements and color mixing parameters.
4. Printers (printing devices)– devices for outputting data from a computer, converting ASCII information codes into corresponding graphic symbols (letters, numbers, signs, etc.) and recording these symbols on paper.
Printers differ from each other in various ways: chromaticity– black and white and color; By way of forming symbols– character printing and character synthesizing; By operating principle– matrix, thermal, inkjet, laser; By printing method– percussive, unaccented; By ways to form strings– serial, parallel; By carriage width– with a wide (375-450 mm) and narrow (250 mm) carriage; By print line length– 80 and 132-136 characters; By character set– up to the full set of ASCII characters; By print speed; By resolution.
5. The main method of converting paper documents into electronic form is scanning- technological process that results in the creation graphic image a paper document, like a “digital photograph” of it. Scanning is carried out using a special device called scanner.
Scanner is an optical-electronic-mechanical device that is designed to convert a visual image of a paper document into a graphic file that saves a raster image of the original document and is sent to a computer for subsequent processing (recognition, editing, etc.).
According to their purpose, scanners are divided into universal(hand, sheet and flatbed) and special(drum scanners, form scanners, bar scanners, slide scanners).
The main characteristics of scanners: scanning resolution (optical, mechanical and interpolation), color depth (bit depth), range of optical densities, size of the scanning area, color matching of the original image to its digital copy, quality of drivers and included software.
Introduction
Remote sensing is a method of obtaining information about an object or phenomenon without direct physical contact with that object. Remote sensing is a subfield of geography. In the modern sense, the term mainly refers to airborne or space-based sensing technologies for the purpose of detecting, classifying and analyzing objects on the earth's surface, as well as the atmosphere and ocean, using propagated signals (for example, electromagnetic radiation). They are divided into active (the signal is first emitted by an aircraft or a space satellite) and passive remote sensing (only the signal from other sources, such as sunlight, is recorded). Passive remote sensing sensors detect a signal emitted or reflected by an object or surrounding area. Reflected sunlight is the most commonly used radiation source detected by passive sensors. Examples of passive remote sensing include digital and film photography, infrared, charge-coupled devices, and radiometers.
Active devices, in turn, emit a signal to scan the object and space, after which the sensor is able to detect and measure the radiation reflected or backscattered by the sensing target. Examples of active remote sensing sensors are radar and lidar, which measure the time delay between emission and detection of the returned signal, thereby determining the location, speed and direction of movement of an object. Remote sensing provides the opportunity to obtain data about dangerous, hard-to-reach and fast-moving objects, and also allows for observations over large areas of terrain. Examples of applications of remote sensing include monitoring deforestation (for example, in the Amazon), the state of glaciers in the Arctic and Antarctic, and measuring ocean depth using a lot. Remote sensing is also replacing expensive and relatively slow methods of collecting information from the Earth's surface, while simultaneously ensuring human non-interference with natural processes in the observed areas or objects. Using orbiting spacecraft, scientists are able to collect and transmit data across different bands of the electromagnetic spectrum, which, when combined with larger airborne and ground-based measurements and analysis, provide the necessary range of data to monitor current phenomena and trends such as El Niño and others. natural phenomena, both in the short and long term. Remote sensing also has applied significance in the field of geosciences (for example, environmental management), agriculture (use and conservation of natural resources), and national security (monitoring of border areas).
Overview of the main remote sensing instruments
Radars are mainly used in air traffic control, early warning, forest cover monitoring, agriculture and large-scale meteorological data acquisition. Doppler radar is used by law enforcement organizations to monitor vehicle speed limits, as well as to obtain meteorological data on wind speed and direction, location and intensity of precipitation. Other types of information obtained include data on ionized gas in the ionosphere. Artificial Aperture Interferometric Radar is used to produce accurate digital elevation models of large areas of terrain.
Laser and radar altimeters on satellites provide a wide range of data. By measuring variations in ocean water levels caused by gravity, these instruments map features of the seafloor with a resolution of about one mile. By measuring the height and wavelength of ocean waves using altimeters, wind speed and direction can be determined, as well as the speed and direction of surface ocean currents.
Ultrasonic (acoustic) and radar sensors are used to measure sea level, tides, and wave direction in coastal marine regions.
Light detection and ranging (LIDAR) technology is well known for its military applications, particularly in laser projectile navigation. LIDARs are also used to detect and measure the concentration of various chemicals in the atmosphere, while LIDAR on board aircraft can be used to measure the heights of objects and phenomena on the ground with greater accuracy than can be achieved using radar technology. Vegetation remote sensing is also one of the main applications of LIDAR.
Radiometers and photometers are the most common instruments used. They detect reflected and emitted radiation in a wide range of frequencies. The most common sensors are visible and infrared, followed by microwave, gamma ray and, less commonly, ultraviolet sensors. These instruments can also be used to detect the emission spectrum of various chemicals, providing data on their concentration in the atmosphere.
Stereo images obtained from aerial photography are often used to probe vegetation on the Earth's surface, as well as to construct topographic maps to develop potential routes through the analysis of terrain images, in combination with modeling of environmental features obtained using terrestrial methods.
Multispectral platforms such as Landsat have been actively used since the 70s. These instruments have been used to construct thematic maps by capturing images at multiple wavelengths of the electromagnetic spectrum (multi-spectrum) and are typically used on Earth observation satellites. Examples of such missions include the Landsat program or the IKONOS satellite. Land cover and land use maps produced by thematic mapping can be used for mineral exploration, detecting and monitoring land use, deforestation, and studying the health of plants and crops, including large tracts of agricultural land or forested areas. Landsat satellite imagery is used by regulators to monitor water quality parameters including Secchi depth, chlorophyll density and total phosphorus. Meteorological satellites are used in meteorology and climatology.
Spectral imaging produces images in which each pixel contains complete spectral information, displaying narrow spectral ranges within a continuous spectrum. Spectral imaging devices are used to solve various problems, including those used in mineralogy, biology, military affairs, and measurements of environmental parameters.
As part of the fight against desertification, remote sensing makes it possible to monitor areas that are at risk in the long term, identify the factors of desertification, assess the depth of their impact, and provide the necessary information to decision-makers to take appropriate environmental protection measures.
Advantages of modern high-resolution space remote sensing:
High spatial resolution – no worse than 1 m in panchromatic mode
High radiometric resolution - no less than 11 bits per pixel in panchromatic mode
Availability of 4 spectral channels, including 1 infrared
Possibility of obtaining stereo photography
Possibility of updating cartographic material at a scale no worse than 1:5000
The frequency of receiving data for the same area on the earth's surface is 1-5 days depending on latitude
Possibility of ordering an area of any shape, incl. shooting extended objects
Possibility of obtaining “perspective” surveys with a deviation from nadir of up to 45 degrees
Large archive – millions of images received
Efficiency: the possibility of starting shooting within 1 day from the date of placing the order
Easy to place an order - no need to obtain permission from government organizations to conduct filming
Ease of processing: the customer receives data ready for use in GIS.
Optical-electronic shooting type
The optical-electronic (OE) method refers to the invisible shooting range (non-photographic). It is only a few decades old. The need for prompt transmission of survey materials from space has led to its intensive development, as well as to scanner camera systems. With a significant variety of design solutions, they are based on a general principle.
The principle of scanning is to read element by element along a narrow strip of radiation reflected by the earth's surface, and the image is scanned due to the movement of the carrier, so it is received continuously.
The following types of surveys are used: route, areal, convergent (stereo survey) and extended object (Fig. “Schemes of OE survey”).
Radiation received from a source from the Earth is converted on a carrier (aircraft or satellite) into an electrical signal, then in the form of a radio signal it is dropped to a ground receiving station, where it is again converted into an electrical signal and recorded on magnetic media. With such shooting, it becomes possible to continuously and quickly receive information for a long time (in real time or with a delay of several hours) and transmit it to the receiving station.
The resolution for the optical-electronic scanning method is:
· extra high
· high,
· average,
· low.
The first scanning systems for imaging in the optical range of the spectrum had a resolution of 1-2 km, but their improvement is proceeding very quickly, and currently a resolution of several meters has been achieved.
Scanning surveys are often performed in a multispectral version. Most scanners operating in the optical range have three identical channels:
· 0.5-0.6 microns;
· 0.6-0.7 microns;
· 0.8-1.1 microns.
To these, in different designs, channels are added in other parts of the spectrum:
in the near infrared,
in thermal infrared,
panchromatic channel providing higher resolution images.
In recent years, there has been a tendency to create hyperspectral imaging systems that record in 10 or more channels.
The advantage of optical-electronic photography. It is their discrete nature that allows photographs to be presented:
As a digital recording on magnetic tape
In the form of a photographic image (photographs).
Related information.
