Flatbed scanners - device, operation, characteristics. General characteristics of scanners

Flatbed scanners tend to be a mix of quality, flexibility and ease of use. They can be used to scan a variety of media, including photographs and films (with the optional use of a slide attachment); they can also be used when scanning text for OCR (optical character recognition) and archiving documents; in addition, flatbed scanners can be used to scan materials of various sizes and thicknesses - from small postage stamps to huge copies of blueprints and 3D objects. To determine the flatbed scanner for your needs, you can use this guide, which covers some of the more important specs that you will find useful to know.

Bit depth and color rendering.

Virtually all scanners today are single pass types with 48-bit color. Gone are the models that required three passes to get full color information from an image in RGB (red, green, blue) mode. Also in the past are 24-bit as well as 36-bit scanners, which were considered a significant achievement of the past for the transfer of about 68.7 billion colors.

Today's single-pass 48-bit scanners are much faster and theoretically recognize up to 250 trillion colors - certainly more than the human eye can distinguish or than a monitor or printer can reproduce. Ignore any scanners other than single-pass flatbeds with 48-bit color. Consider models with fewer bits (such as 42-bit) only if the scanner has other specifications that its high bit counterpart does not, such as proprietary technology or special features that compensate for low bit depth.

Permission.

The resolution of a scanner determines the level of detail that can be scanned; the higher the resolution, the clearer the resulting image will be. There are two types of resolution: optical and interpolation. Optical resolution has more important specifications. The scanner's interpolated resolution is only useful in certain applications, such as scanning line art to provide smooth edges where high resolution can result in a "jagged" surface.

Most flatbed scanners today have peculiar specifications for optical resolution, ranging from 2400 to 4800 dpi. Any scanner with this resolution indicates the right choice, because. these characteristics are more than adequate for scanning fine details or enlarging images for most printing applications. Remember, too, that scanning an image at the scanner's maximum resolution is like enlarging a file to an uncontrollable size—with no apparent benefit in clarity or image quality. So forget the high resolution struggles of the past, when every manufacturer considered creating the highest resolution of their product as an ace in the never ending competition. Instead, look today for other features of flatbed scanners that might be more useful to you, or consider the high resolution capabilities combined with other features when choosing the right scanner for you.

CCD vs. CIS sensor technology.

Image sensors in flatbed scanners can be of two types - CCD or CIS. Scanners with CCD (Charge Coupled Device) sensors use a system of mirrors and lenses to change the direction of light reflected from the base document onto the CCD. Due to special optical devices, the production of CCD scanners is more expensive and they are much larger in size compared to CIS counterparts. The image quality obtained with these scanners, however, is much higher than that of similar CIS models.

CIS, or Contact Image Sensor, is a relatively recent development in which an array of sensing elements is located under the scanner bed so that the sensors directly capture reflected light. Because CIS scanners do not require a complex optical system, they are much cheaper to manufacture and they are smaller in size, and portable and light enough models are ideal for home desktop computers. CIS sensors also include built-in logic boards that consume less power than CCDs. But due to the fact that the integrated logic board takes up space that is usually used for mirrors and lenses in CCD models, the quality of images obtained with CIS scanners is lower. As a result, most people, despite the lower price of CIS scanners, prefer to pay more and purchase high quality CCD models instead.

Connectivity and interface.

Most scanners today feature USB ports - either high-speed USB (USB 2.0) on the latest models, or standard USB 1.1. Hi-Speed USB is compatible with USB 1.1, and has a data transfer rate of 480 Mbps. More advanced scanner models may also include a FireWire interface, allowing the scanners to be used in modern audio/video transmissions. Scanners with a USB or FireWire interface can connect to other devices without the need to plug them into a network. Older models of scanners include SCSI (Small Computer System Interface) or parallel ports, but you should not consider these older models unless you intend to use them to connect to older computers. If you are going to buy a flatbed scanner, you should buy any scanner with a high speed USB port, also consider models with dual high speed USB and FireWire interfaces to expand the network of possible connections of external devices.

Scanning speed.

Speed characteristics in flatbed scanners are difficult to determine unless the manufacturer specifies the specific conditions under which the material must be scanned. Scanning speed can vary from a few seconds to several minutes, depending on a wide variety of factors. For example, to compare the scanning speed of two models, you need to know the size of the material being scanned, the resolution settings, the interface used, the processing speed, and the power of the computer to which the scanner is connected. Carefully check the speed characteristics, it will help you to make a test scan performed on the model of your choice. It can also help to make the right choice by browsing special computer magazines and websites devoted to this topic, since. there are benchmark results showing the full picture of how fast a scanner can run.

Dimensions of the flatbed scanner.

Most flatbed scanners today start with a standard 8.5 x 11.7 inch flatbed, roughly the size of a letter or document. The following are various configurations, including 8.5 x 14 inches for standard paper and 12 x 17 inches for tabloid paper. It is generally recommended to consider scanners with a plate size that is larger than the minimum, i.e. larger than 8.5 x 11.7 inches. Not only can you scan large materials, but you can also group several small pieces on the scanner and scan in batches to save time and labor.

dynamic range.

The dynamic range of a scanner measures how well it captures the tonal range of an image, which ranges from bright lights to dark shadows. Dynamic range is measured on a scale from 0.0 (pure white) to 4.0 (pure black), and a simple number that indicates the light output level of the device. The minimum and maximum light concentrations that can be recognized by the scanner are called Dmin and Dmax, respectively. If a scanner's Dmin is 0.2 and its Dmax is 3.0, then its dynamic range is 2.8.

While dynamic range is a metric that is constantly debated, it is actually an important characteristic mainly for photo-scanning devices used to scan negatives and transparencies, as these types of media have a wider range of colors than photographs, and for which a high dynamic range is essential. Most flatbed scanners have a range of 2.8 to 3.0, but don't worry if you can't find those numbers, it's not that important for the average user who scans photos and all sorts of images.

Software.

When choosing a scanner, carefully consider the software that comes with it. It includes its own scanner driver along with additional software such as photo editing software such as Adobe Photoshop, optical character recognition software such as ABBYY FineReader Sprint for text scanning, color calibration software for high quality scanning, and even photo recovery software. , such as Digital Ice. Also don't forget to check the patent.

Scanners– devices for automatic reading and input of graphic information (texts, graphs, figures, drawings) into a PC.

The file created by the scanner is called a bitmap.

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

There are the following types of scanners:

 manual,

 tablets,

 drums,

 form scanners,

 Barcode scanners.

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

Flatbed Scanner . Its device provides for the movement of the scanning head (line of LEDs) relative to the original using a stepper motor.

Drum Scanners . In scanners of this type, the source material is fixed on the cylindrical surface of a drum that rotates at high speed.

Form Scanners are intended for data entry from standard forms filled out "by hand" (population census, elections).

Barcode Scanners designed to enter data encoded in the form of a barcode.

The most common are flatbed scanners.

The principle of operation is that a beam of light reflected from the surface of a material is fixed by special elements (CCDs) - charge-coupled devices.

The main consumer parameters of flatbed scanners are:

 resolution,

 connection type

 dynamic range

 productivity

Reading takes place using a CCD matrix. For a scanner, the CCD matrix is made in the form of a ruler, for cameras - in the form of a field. The more elements in the CCD, the better.

Resolution is determined by the number of CCD elements per 1 inch. A typical indicator for office use is 1200 - 2400 dpi (dots perinch) - dots per inch, for professional graphics 4800 * 9600.

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

The dynamic range of a scanner is characterized by its ability to distinguish nearby shades. Dynamic range is defined as the logarithm of the ratio of the brightness of the brightest areas to the darkest areas. A typical indicator for office scanners is 1.8 - 2.0.

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

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

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

What if you need to send an image printed on paper by e-mail? Probably, everyone already knows such a device as a scanner. It has repeatedly helped people save old photographs taken by our grandparents, convert some important documents into electronic format, without having their source on a PC.

In general, a scanner is a useful thing and is now simply irreplaceable in many offices. To correctly determine which model you need, you should study the main characteristics of the scanner.

What is this?

It is better not to refer to scientific terms, but to explain in simple terms what kind of device it is. The scanner is responsible for performing the reading process, which is directed to a flat storage medium (such as paper). Ultimately, the user receives a digital document for transmission at a distance or storage in electronic format. Scanning leads to the creation of a digital image of the external image of the object thanks to the ADC. After that, the picture is sent to the computer using the input / output system.

First attempts

Few people know, but the main characteristics of the scanner have been known to researchers since 1857. Then an alternative to the modern device was created by the abbot from Florence, Giovanni Caselli. His device worked very primitively relative to current technology. Then, in order to transmit an image over a distance, it was necessary to apply it to the drum using conductive ink, and later read the image with a needle. Such a device was called a pantelegraph.

Half a century later, a German physicist conducted his experiment, during which telefax was patented. Arthur Korn developed the photoelectric scanning technique. Its principle was not simple: the picture was attached to the same drum, but already transparent. The lamp was so fixed that the stream of light could move. It passed through the original image and was directed to the selenium photodetector, and then penetrated through the prism and lens.

The faster semiconductors developed, the faster the photodetector improved. Despite the fact that the tablet method was later invented, the principle itself remained practically unchanged.

Characteristics

Before you deal with the views, you need to pay attention to the technical characteristics of the scanner. There is a whole range of them, and there is no generally accepted classification. Each parameter depends on the intended purpose of the instrument. Nevertheless, there are basic characteristics by which you should choose a scanner. Among them are the speed of work, color depth, resolution of the resulting image, etc.

Beauty is in the details

The characteristics of the scanner are varied, but the resolution is one of the main parameters. In simple terms: this property is responsible for the size of the smallest details of the picture that will be transmitted during scanning. Resolution is specified in dpi. This value indicates the number of visible dots per inch of the picture. Typically, the manufacturer indicates the performance of all three resolutions:

mechanical;
optical;
interpolation.

The first is necessary in order to determine the placement of the carriage with the CCD ruler while moving through the image. The fact that the mechanical resolution is twice the optical resolution is used by the manufacturer against an incompetent user. In TX, he indicates that the optical value is 300x600 dpi. But if the device does not have interpolation, then it will work with a minimum value of 300 dpi.

The interpolation resolution is responsible for the size that can be obtained by scaling the image by 16 times. In principle, this is the least important parameter, and it practically does not carry any additional data. But the manufacturer can also use it against the buyer, indicating 4800 dpi on the box. Such a figure may impress an ignorant person. But everyone who does not know the characteristics of the scanner, but is going to buy this device for himself, should take into account that the real optical value can be only 300 dpi.

The main parameter is the optical resolution. To determine it, you need to calculate the concentration of elements in the photosensitive ruler. To do this, you need to divide the number of parts on it by its width. This parameter, as mentioned earlier, is the most significant in determining the detail of the picture. Therefore, it can rarely be found on the box with the device, as both the manufacturer and the seller are trying to hide the real indicators.

"Dry" figures

As mentioned earlier, it is not easy to choose such a device. The characteristics of scanners can confuse an inexperienced buyer, so it is better to delve into each parameter before purchasing. The next after the resolution is the bit depth, or hue depth. This characteristic indicates the number of bits that are required to store color information about each pixel. Black and white scanners require the least amount of memory. They have one rank. Monochrome is slightly larger - 8, and color - 24 bits. Scanners in the more expensive segment may be 36-bit.

Color depth is external and internal. These are the figures indicated by the manufacturer. The internal one is characterized by the bitness of the analog-to-digital transformer, which helps to determine the number of colors that the scanner can “see”. External depth is the number of shades that the device is able to transfer to the PC.

If you need a device for the office or home, the usual bit depth is also suitable - 24 bits. If you need a scanner for printing and similar organizations, it is better to look for a 48-bit device.

Optical density

The characteristics of the scanner do not end there. There is a maximum If you do not go into details and scientific explanations, this is the ability of the device to scan dark pictures: the more sensitive the device, the better the dark areas of the image are digitized.

Along with this parameter, there is an interval of optical density. It can be calculated from It is equal to the ratio of the amount of light falling on the original to the amount reflected. On average, the range for 24-bit bit depth should be 1.8-2.3 D.

Speed

This parameter is also often forgotten to be indicated or completely lied to. However, the rate of scanning depends on several factors. First of all, this is the resolution and size of the original. The speed can indicate the number of pages per minute, or simply the time at which one sheet is processed. There is also a measurement of scanned lines per second.

The size of the scanned area can also be varied. The most common solution is an A4 sheet. Such models are found in offices and homes. Some enterprises may use the A3 format. For handheld scanners, the strip size is 11 cm.

Interface

Not always the characteristics of the scanner are of particular importance. You can send a device parameter such as an interface to this category. It can be of several types. This includes your own interface from the developer. It was used earlier in scanner models. Its popularity faded after the ability to update the PC operating system. This was due to the fact that after the sale of one or another scanner lost the optimization of its interface for another system, and therefore did not function at all.

The following interface was received, which can now be found in the younger models of flatbed scanners. These devices are quite mediocre and do not stand out in any way. They are usually used to scan a photo or a couple of pages of text.

The PCMCIA interface is also rare, but SCSI remains the standard for devices with high quality and performance. Now more powerful machines with 30 and 36 bits are being produced with this interface.

USB interface is the latest and trendy option. It is actively recommended for many models, however, it is not good enough for high-performance devices.

Light source

This parameter is rarely taken into account when choosing a scanner. There are three types of lighting:

xenon;
fluorescent;
LED.

Xenon lamps are small, long lasting and have a short warm-up time. Fluorescent lighting is quite cheap, but it will also last a very long time. LEDs are small, consume little power and heat up quickly. Usually, it is the latest LED scanners that are considered to be of higher quality.

Diversity

After the scanner itself appeared, it began to be modified and take on different forms. Now this device can be classified according to a number of parameters. The types of scanners and their characteristics have now become generally accepted, and so far no technological innovations have been observed in this area.

To break these devices into categories, you need to study the following signs:

imaging method;
the structure of the kinematic mechanism;
type of image;
characteristics of the original;
interfaces: hardware and software.

Kinds

So, according to all the above parameters, you can choose a scanner for yourself. He can be:

tablet;
book;
manual;
leaf-spun;
planetary;
drum;
ultrasonic, etc.

In general, there are a lot of types of scanners. We will talk about the main and most popular.

Tablet is currently the most popular and convenient. Typically, models of this type are very high quality and fast. Outwardly, they look like a tablet, which is why they got that name. To scan an image with such a device, you need to open the lid, put the sheet face down on the glass, close the lid and press "start".

The handheld scanner does not have a motor. Therefore, to process the image, you need to move it yourself. The main advantage of such models is their price. But there are too many disadvantages: poor resolution, low scan quality and low speed.

The book scanner is designed for processing brochure documents. To scan the necessary information, it must be placed not face down, as in a tablet, but up. The quality is very good.

The sheet-spun scanner is not very comfortable. To process the document, the sheet is inserted into the slot and pulled through the shafts inside. This scanner works with certain sizes and single sheets.

The planetary apparatus works with papers that are easily damaged. It eliminates contact with the object, due to which the integrity of the material can be maintained.

Drum devices are found at printing enterprises and produce a high-quality image. Slide scanners work with film slides. We meet barcode scanners every time we come to the checkout in the store. 3D device is something newfangled. It can scan real objects, which are digitized and turned into a 3D model. An ultrasound scanner is a famous ultrasound used in medicine to examine internal organs.

Four in one

There is a united copier module, facsimile mechanism, printer, scanner. Its characteristics are different. Basically, such devices can be inkjet, laser or LED printing technology. Like any scanner, the MFP can be color or monochrome.

The main advantage of such a device is to save space at home or in the office. The user does not need to move the paper from one place to another. It is convenient to work with one device. Also, MFPs have a fairly low price, relative to the amount that would have to be paid for a separate purchase of each device.

New in 2016

When you have familiarized yourself with the characteristics of the scanner, you can start searching for this device. This year, a lot of new models have been released that may interest the user. For example, an HP ScanJet scanner, whose performance is impressive, can cost as little as 2 thousand rubles. At the same time, you will have access to a device with a color scanning depth of 48 bits, a popular USB 2.0 connector and compatibility with many operating systems. In general, HP scanners, whose characteristics have always been at the highest level, are market leaders in this segment. The company also has excellent models of multifunctional devices.

This year, those who impressed not only with functions, but also with the price, appeared on the market. The characteristics of the Pro scanner are really very high. In addition to the fact that this tablet device has an adapter for film sliders and a USB 2.0 interface, its main characteristic is a resolution of 6400 × 9600 dpi. Along with these parameters, the price of the scanner ranges from 80 to 100 thousand rubles.

Among the novelties there is also a budget option. The performance of the Canon CanoScan 9000F is mediocre. Its resolution is 9600×9600 dpi. The price is 12 thousand rubles. Reviews about this model on the "four". The thing is that marketers are starting their “song” again, talking about unprecedented parameters. In fact, instead of 48 bits, we get only 12. That is, in each channel, instead of 16, only 12 bits. Nevertheless, there are those who are satisfied with the speed, high resolution and quality of the materials of the device itself.

In general, to choose a good scanner, you do not need to be a scientist, especially for ordinary users. Large resolution is not required for and photocopies. Ultra-high speed is also not important. Therefore, it is better to choose the scanner that you really need in its full functionality.

The dot matrix printer forms characters with several needles located in the printer head. The paper is pulled in by a shaft, and an ink ribbon is placed between the paper and the printer head. Dot-matrix (dot-matrix) printers are used less and less nowadays. The advantages of these printers: satisfactory print speed and versatility, which consists in the ability to work with any paper, as well as the low cost of prints. Disadvantage: poor quality of printed products, especially graphics. Color printing is not possible. Another drawback: the needle printer is a mechanical device, and the operation of mechanical components is always accompanied by noise.

Inkjet printers

In inkjet printers, the image is formed by microscopic droplets of special ink flying onto the paper through small holes. Piezocrystals are used as elements that push out jets of ink (Fig. 2.9).

Rice. 2.9.

Laser printers

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

Rice. 2.10.

The main parameters of laser printers include:

resolution, dpi (dots per inch - dots per inch);
productivity (pages per minute); Medium-capacity laser printers print 6-10 pages per minute. High performance network laser printers can print up to 20 or more pages per minute. Of course, these are conditional figures, since printing complex graphic images on the same printer will take much longer than printing text;
the paper size you are using. Most laser printers can print on A4 paper, less commonly A3;
the amount of own RAM. A laser printer processes entire pages, which involves a lot of calculations. Most often, black and white laser printers use memory from 2 to 16 MB.

Scanners

New term

Scanner- a device for copying graphic and textual information in order to enter it into a computer. There are three types of scanners - handheld, flatbed and drum.

Hand scanners are relatively inexpensive devices of a small size. You often see them in stores, at the checkout. They serve there to read the barcode with the price of the goods. The disadvantages of a handheld scanner include the dependence of the scan quality on the user's skills and the inability to scan relatively large images in their entirety.

IN drum scanners the starting material is fixed on the cylindrical surface of the drum rotating at high speed. Devices of this type provide the highest resolution in the range of 2400-5000 dpi. Currently, drum scanners are used mainly in the printing industry.

For home users and offices are most commonly used flatbed scanners(Fig. 2.11).

Rice. 2.11.

Flatbed scanners are designed to capture graphic information from transparent or opaque sheet material. Their standard format is A4, so not only a separate sheet or page, but also a whole unfolded book or magazine can be placed under the cover of such a scanner "face" on the glass. In this way, flatbed scanners resemble photocopiers. The main elements of the scanner are a semiconductor laser and a semiconductor photodetector.

The principle of operation of these devices is that a beam of light reflected from the surface of a material (or passed through a transparent material) is fixed by special elements called charge-coupled devices (CCDs). When the scanner is swiped over text or an image, a laser beam travels across the sheet, scans it, and reflects it onto a photosensitive semiconductor element. The photocell converts the light signal into an electrical signal, which is then transmitted via a bus to a computer. In it, the signal is converted into a digital form containing information about the coordinates and color of each pixel in the image. And, finally, at the last stage, the received information about the image is written to disk as a file.

Specifications of scanners

In order to choose the right type of scanner, and, accordingly, to maximize its capabilities for the implementation of the tasks, it is necessary to understand the technical characteristics of scanners and the existing terminology.

Resolution is the main characteristic of a scanner. During the scanning process, the image is divided into separate dots, the size of which is determined by the characteristics of the optical system and photocells. By optical resolution is meant the number of such points that fit on a segment of a certain length. Device specifications may list different horizontal and vertical resolutions. For example, a setting of 300x600 dpi means that each square inch of the image is divided into 300 dots horizontally and 600 dots vertically. The higher the resolution, the more information about the original can be entered into the computer and further processed.
Scanner performance is characterized by the duration of scanning a sheet of paper of a standard size and depends both on the perfection of the mechanical part of the device and on the type of interface used to interface with a computer. Basic models more commonly use scanner communication via a USB port. In professional scanners - SCSI.
The dynamic range of a scanner is determined by the logarithm of the ratio of the brightness of the lightest areas of an image to the brightness of the darkest areas. The typical value for office scanners is 1.8-2.0, and for professional scanners it ranges from 2.5 (for opaque materials) to 3.5 (for transparent materials).
The color depth of the scanner reflects the bit depth of the analog-to-digital converter, that is, it is a characteristic that shows how accurate the color information of each point of the scanned image is. The color depth of 1 bit corresponds to the black and white mode of the scanner, each point can only be black or white. In gray mode, the color depth is typically 8 bits. This corresponds to 256 shades of gray. This is the number of shades possible for each point. Color scanning is nothing but gray mode scanning with different filters (red, blue, green). 256 hues for each of the three components give a total of 16.7 million possible color combinations (24-bit image). It would seem that 24 bit is enough to accurately reproduce any shade, however, with further adjustment of gamma, brightness or contrast, the size of the palette is significantly reduced, especially at the edges of the spectrum, part of the data is lost. It is for this reason that leading manufacturers are already releasing models with a color depth of 36 and even 48 bit. With inevitable data loss, the "spare" bits allow you to get a real 24-bit image.

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