How digital printers work. How a digital camera works How the system works

After the transition of on-air broadcasting from the analog standard to digital, it became necessary to purchase special devices for older TVs. Everything modern models TV receivers are equipped with an appropriate tuner. However, not everyone is ready to change their TV because of this. Knowing how a digital TV set-top box works and the features of choosing a device, you can buy an inexpensive and effective device.

Purpose of the device

Thanks to digital set-top box to the TV, you can not only watch broadcasting in the new standard, but also significantly expand the capabilities of the TV receiver. On sale is a large number of models that differ in cost and functionality. Among the main functions performed by the console, you can note:

• Play media files from a USB flash drive.
• TV broadcast recording in ts format on external drive.
• Possibility to stop live view.
• Thanks to the TimeShift function, the broadcast of a TV program can be postponed.

Some budget modern TV models have much less functionality, although they are equipped with a DVB-T2 tuner. In such a situation, the prefix will be able to significantly expand its capabilities.

It should also be said about another type of tuners - Smart TV set-top boxes. They give users even more options.

These devices can work in one of two ways:

• All files are stored on the built-in media; to run the necessary software, you must first install it.
• used to store work information. cloud services, and the device can only function when connected to the Internet.

The main advantage of Smart set-top boxes is the ability to access various resources on the Internet and display information on the TV screen.

Such tuners can be equipped with several slots for connecting memory cards at once, they support a large number of multimedia formats.

Criterias of choice

It should be recognized that the TV set-top box for viewing digital television is not the most complex consumer electronic appliance.

But even considering the relatively low cost of these devices, it is necessary to make right choice. There are several criteria that must be kept in mind when going to the store.

Broadcast standards

This question is the most important when choosing a device. Since Russia uses the DVB-T2 digital television standard, TV set-top box must support it. This is a universal solution that suits users of all regions of the country. In addition, the picture quality of DVB-T2 is better than that of DVB-T1.

Two more standards should also be noted - DVB-S and DVB-S2. They are used to broadcast satellite television. If the set-top box supports them, then the user can connect it to a satellite dish and broadcast the received signal directly to the TV without using a receiver.

Today, many cable TV providers use the DVB-C standard. This gives them the ability to encode the signal. To gain access to it, special modules are required. If the device will be used to receive cable television, then it must also support this standard.

Connection methods

If the tuner is purchased to work with an old TV, then it must have three tulip or RCA connectors. One of them is used to output the video signal, while the other two transmit sound in stereo. Most set-top boxes today are equipped with an HDMI connector. This is a modern standard used for the simultaneous transmission of video and audio signals.

The presence of USB ports suggests that the device can be used as a multimedia player. In addition, an external drive is connected to them for recording TV programs, if such a function is supported by the set-top box.

It is also worth paying attention to the end-to-end antenna output, thanks to which two TV receivers can be connected to the set-top box at once without the use of splitters.

Functionality

Since digital tuners are capable of not only receiving a signal of the required standard, it is worth getting acquainted with their useful features. One of them is TimeShift (delayed viewing). Thanks to her, the broadcast of a TV show can be paused and not miss an interesting moment.

You should also pay attention to the Personal option. video recorder(PVR). With its help, you can record programs if it is not possible to watch them in live. It is quite obvious that for this external storage required. Many modern set-top box models can be used as a multimedia player due to the support of popular formats. The TV guide function allows you to find out the weekly schedule for all available channels.

Popular consoles

V retail chains you can find a large number of set-top boxes, but it is sometimes quite difficult to give preference to one or another model, even if you know the selection criteria. After getting acquainted with the review of popular set-top boxes, it will be easier to make a decision.

Model Supra SDT-94

The device looks stylish and has a low cost.

The prefix provides the ability to record programs on a flash drive, as well as view multimedia content.

The device is connected to the TV using "tulips" or HDMI cable. It should be noted that it is worth using the second option, since the picture quality will be much better.

Among the advantages of the model are:

• Low cost.
• Confident signal reception.
• Ease of setup.
• The presence of an HDMI connector.
• Parental control feature.

If we talk about the shortcomings, then most often users note not very Good work IR receiver.

To control the set-top box, you literally have to aim at it with the remote control. It is also worth noting the image jumps when connected to a TV using RCA connectors.

Device Oriel 963

A distinctive feature of the model is the ease of setup. The prefix will be quickly dealt with by people who do not understand anything in electronic household appliances. It is also worth noting that the prefix has an aluminum body. Thanks to this, it not only looks stylish, but also does not overheat during operation.

You can connect not only a flash drive to the USB connector, but also external HDD. The device has a built-in media player that handles all popular formats perfectly. Do not forget about the delayed viewing function, which is sometimes extremely necessary.

The model has the following advantages:

• High sensitivity IR receiver.
• The control buttons are located on the front panel.
• Allows you to record desired TV programs.
• Has many connectors.

The device has only one drawback - not the most convenient menu. Otherwise, there are no complaints about Oriel 963.

Device B-Color DC1302

The device is easy to use and does an excellent job of receiving a DVB-T2 signal. Support for AC3 audio format makes this model a real media player. The fact is that in large video files, sound is recorded using this codec. Control buttons located on the front panel will make working with the console even more convenient.

It should be noted that the B-Color DC 1302 has support for HD channels. The metal case is an excellent heatsink and prevents the set-top box from overheating during operation. Among the shortcomings, only a relatively short length of the power cord, as well as a slightly slower channel switching can be noted.

The choice of a device for watching digital TV largely depends on the individual needs of the user. Not every person will overpay for additional functions, because he is ready to limit himself to only the main one. Before going to the store, you should immediately decide for what purposes you plan to use the tuner, not counting the main purpose.

> How does a digital camera work

A digital camera captures light and focuses it through a lens onto a sensor made of silicon. It consists of a grid of small photocells that are sensitive to light. Each photocell is called a pixel, short for picture element. Millions of these individual pixels reside in the sensor of a digital SLR.

The digital camera selects the light of our world, or outer space, spatially, tonally and in time. Spatial sampling means that the image in the camera is divided into a rectangular grid of pixels. Tonal sampling means that the ever-changing luminosity tones in nature are broken down into discrete discrete tone steps. If there are enough samples, both spatially and tonally, we perceive them as a true representation of the original scene. The sampling time means that we make an exposure of a given duration.

Our eyes also perceive the world on the basis of a few tenths of a second when the amount of light is the same as during daylight hours. In low light conditions, eye exposure, or integration time, may increase to several seconds. That's why we can see more detailed information with a telescope if we look at a faint object for a long time.

The eye is a relatively sensitive detector. It can detect a single photon, but this information is not transmitted to the brain because it does not exceed the minimum signal-to-noise ratio threshold in the noise filtering circuitry in the visual system. This threshold causes the arrival of several photons for their fixation by the brain. A digital camera is almost as sensitive as the eyes, and both are much more sensitive than photographic film, which requires many photons to detect.

These are the long exposure time frames that really make the magic of digital astrophotography possible. The true power of a digital sensor comes from its ability to integrate, or collect, photons over more long periods time than eyes. This is why we can record data at slow shutter speeds that are invisible to the eye, even through a large telescope.

CCD and CMOD sensors work similarly to each other in absorbing photons, generating electrons, and storing them, but differ in how charge is transferred and where it is converted to voltage. And both have a digital output.

The entire digital image file is a collection of numbers that represent the brightness and location values ​​for each square in the array. These numbers are stored in a file that our computers can work with.

Not all pixels are sensitive to light, only photodiode ones. The percentage of pixels that are light sensitive is called the fill factor. For some sensors, such as CMOD, the fill factor may only be 30 to 40 percent of the total area of ​​the photocells. The rest of the area on the CMOD sensor consists of electronic circuits such as amplifiers and noise reduction circuits.

Since the photosensitive area is small compared to the size of the pixels, the overall sensitivity of the chip is reduced. To increase the fill factor, manufacturers use micro-lenses to direct photons, which hit non-sensitive areas and go unnoticed, onto the photodiode.

Electrons are generated as long as photons impact the sensor during the duration of exposure or integration. They are stored in a potential well until the end of irradiation. The size of the well is called the total capacity, and this determines how many electrons can be collected before the well fills up and registers in full. In some sensors, after filling one well, electrons can spill over into adjacent wells, causing blooming, which is visible as vertical peaks on bright stars. Some cameras have anti-yumming capabilities to reduce or prevent this phenomenon. Most DSLR cameras control bloom very well and this is not a problem for astrophotography.

The number of electrons that can accumulate in the well determines dynamic range sensor and also a brightness range from black to white, where the camera can capture detail in both the weak and bright areas of the scene. After noise correction, a sensor with a larger capacitance usually has a greater dynamic range. A low-noise sensor helps improve dynamic range and enhance detail in low-light areas.

Not every photon that hits the detector will be registered. The amount to be registered is determined by the quantum efficiency of the sensor. Quantum efficiency is measured as a percentage. If a sensor has a quantum efficiency of 40 percent, this means that four out of every ten photons that hit the sensor will be detected and converted into electrons. According to Roger N. Clarke, quantum efficiency in modern digital SLR cameras is between 20 and 50 percent, depending on the wavelength. Top Models Astronomical CCD cameras can have quantum efficiencies of up to 80 percent or more, although this applies to grayscale images.

The number of electrons collected in the well is proportional to the number of photons that are registered. The electrons in the well are then converted into voltage. This charge is an analog (continuously changing) signal and is typically very small and must be amplified before it can be digitized. The output amplifier performs this function by matching the sensor's output voltage range to the range input voltage AD Converter. The AD converter converts this data into a binary number.

When the AD converter digitizes the dynamic range, it splits it into step by step mode. The total number of steps is given by the bit depth of the converter. Most DSLR cameras work with 12 bits (4096 steps) of tonal depth.

The output of a sensor is technically called an analog-to-digital unit (ADU) or digital number (DN). The number of electrons in an ADU is determined by the gain of the system. A gain of 4 means that the AD converter digitizes the signal so that each ADU corresponds to 4 electrons.

The ISO exposure class corresponds to the film speed class. This is a general assessment of sensitivity to light. Digital camera sensors have only one sensitivity, but allow different ISO settings by changing the camera's gain. When the gain is doubled, then the number of electrons in the ADU is reduced by a factor of 2.

By increasing the ISO in a digital camera, fewer electrons are converted into one ADU. Increasing ISO reduces dynamic range. At ISO 1600, only about 1/16 of the sensor's potential well can be used. This can be useful for astronomical imaging of dim objects from which electrons cannot otherwise be collected to fill the potential well. The camera only converts a small number of electrons from these rare photons and maps this limited dynamic range to the full bit depth, thus allowing a great deal of differentiation between steps. It also gives more steps to work with these faint data when it is stretched later in processing to increase contrast and visibility.

For each pixel in the sensor, brightness data, represented by a number from 0 to 4095 for a 12-bit AD converter, along with pixel location coordinates, is stored in a file. This data may be temporarily stored in the camera's built-in buffer memory before being written to the camera's removable memory card.

This file of numbers is reconstructed into an image when it is displayed on a computer monitor or printed.

These are the numbers that are produced by the digitization process that we can work with on our computers. Digits are represented as bits, and the representation is "binary digits". Bits use base 2 in binary system reckoning, where there are only digits one and zero, and not based on 10, where there are digits from 0 to 9, which is what we usually work with. Computers use binary numbers, because the transistors from which they are made have only two states, on and off, which are represented by the numbers one and zero, respectively. All numbers can be represented in this way. This is what makes computers so powerful at working with numbers, transistors do it very quickly.

Spatial sampling

The photosensitive element in the camera's matrix corresponds one to one with the pixels in the digital image when it is output. Many people also refer to such elements in a camera's sensor by the generic term "pixels". These elements are arranged in a rectangular array. In the Canon 20D, the array is 3504 x 2336 pixels for a total of 8.2 million pixels. This grid can be thought of as a chessboard where each square is very small. The squares are so small that, when viewed from a distance, they make the eye and brain think that the image is continuous. If you enlarge any digital image large enough, you will be able to see the individual pixels. When this happens, we call the image "fuzzy".

A color image is actually made up of three separate channels, one each for red, green, and blue. Because of the way color is perceived by the eye and brain, all the colors of the rainbow can be created from these three primary colors.

Although a digital camera can record 12 bits or 4096 steps of brightness information, almost all output devices can only display 8 bits or 256 steps per color channel. The original 12-bit (2^12 = 4096) input must be converted to 8-bit (2^8 = 256) data for output.

In the example above, the nominal pixel has a brightness level of 252 in the red channel, 231 in the green channel, and 217 in the blue signal channel. The brightness of each color can range from 0 to 255, with 256 total steps in each color channel when displayed on a computer monitor or when output on a desktop printer. Zero means pure black and 255 indicates pure white.

256 colors each of red, green and blue may not sound like much, but it's actually a huge number because 256 x 256 x 256 is over 16 million individual colors.

Tonal sampling

The light and tones in the world change continuously. After sunset on a clear day, the sky in the west varies from bright near the horizon to deep blue overhead. These shades of blue are constantly changing. They smoothly transition from light to dark.

Digital cameras, when measuring light, break its continuously changing signals into discrete steps that can be represented by numbers (digits). They digitize the image.

64 steps

32 steps

16 steps

Thanks to the way our visual system uses, if we separate continuous signals in enough small discrete steps, we can trick the eye into thinking it's a continuous signal, even though it isn't.

In the examples above, we can see the effect of the different number of tones as we go from black to white. We can clearly differentiate a small number of tones as discontinuity. But as the number increases, somewhere around 128 steps, they seem to be continuous to our perception.

Computers and numbers

Because the computer is very powerful tool when manipulating numbers, we can perform various operations on those numbers quickly and easily.

For example, contrast is defined as the difference in brightness between adjacent pixels. For contrast, there must be a difference, so that one pixel is brighter and the other pixel is darker. We can very easily increase the contrast by simply adding the number of steps in brightness for a bright pixel and subtracting the number of steps from the brightness value of a dark pixel.

A color in an image is represented by the brightness value of a pixel in each of the three color channels - red, green, and blue - that make up the color information. We can just as easily change the color of a pixel, or group of pixels, by simply changing the number.

We can perform other tricks, such as increasing the apparent sharpness of an image by increasing the contrast of the edges of objects in the image through a process called unsharp masking.

Representing an image as a number allows us to completely control it. And, since the image is a collection of numbers, it can be duplicated any number of times without losing quality.

Linear or non-linear data

The write response of a digital sensor is proportional to the number of photons that hit it. The response is linear. Unlike photographic film, digital sensors double the recorded signal when the number of photons hitting the sensor is doubled. Digital sensors are also interchangeable, as are most photographic films.

The data captured by the CMOS sensor in a digital SLR and written to the raw file is linear. Linear data tends to look very dark compared to normal photographs (see image below).

Linear curve

The human visual perception of brightness is better described by a logarithmic curve than a linear curve. Other human senses, such as hearing, and even taste, are also logarithmic. This means that we are better at discerning differences at the lower end of the perceptual scale than we are at the high end. For example, we can very easily distinguish between one pound and two pounds by weight when we lift them up. But we have difficulty distinguishing between 100 pounds and 101 pounds. However, the difference is the same, one pound.

logarithmic curve

Normal photographs on film are also recorded in a non-linear manner, which is similar to the way humans perceive. That's why we can keep the slide up to the light and it looks like a reasonable representation of the original scene without any additional modifications.

Because the human visual perception system does not work in a linear fashion, a non-linear law must be applied when "stretching" linear data from a DSLR to make the tonality of the photographs better match our visual perception. These non-linear corrections are made by software inside the camera when the image is written to a file in JPEG format. If the raw file is stored in the camera, these non-linear adjustments are made in software later when the data is opened in an image processing program.

In the image examples shown above, a screenshot of Photoshop's Curves dialog has been included in the image so we can see the comparison between linear data and the same data with non-linear adjustments. The curve in the dark image is linear, that is, a straight line. The curve in the light image is shown with a stretch that should be applied to the data to bring it closer to our visual perception.

The curve represents the input and output brightness values ​​of the pixels in the image. Black in the lower left corner and white in the upper right corner. gray tones in between. When the line is straight, an input that runs horizontally along the bottom corresponds to an output that runs vertically along the left side.

The inset shows that when the straight line is pulled up so that its slope increases, the contrast of that part of the curve and the corresponding tones in the image increases. In the example above, you can see that the tone at the specified point is much easier to create. All tones in the image below this point on the curve, and the corresponding tones in the image, are stretched away from each other and their contrast is increased.

That's why it's important to work with high bit depth when working with raw images. Due to the high tension and increase in contrast that is needed, the tones are stretched. If we have many tones and the depth of the high tone allows, then they can be smoothly redistributed. If we don't have enough tones to work with, we risk posterization and banding when we stretch the data.

In a bright image, the slope of the top of the curve decreases in the bright areas of the image. This compresses the tones and reduces the contrast of those tones in the image.

This is what allows this data to be accessed in a linear fashion at high bit depth, which makes DSLR and CCD images so powerful for creating astrophotos. This allows us to subtract the sky background and light pollution. This gives us the ability to control non-linear adjustments and stretch the data. These settings bring out the details of astronomical objects that are hidden deep in what we think of as the shadow areas of a normal photograph.

In this issue, I'm going to start a "long-playing" topic about how a digital camera is arranged and how it works, what all sorts of buzzwords like "bracketing" and "exposure compensation" mean, and, most importantly, how to purposefully use all this.

In general, a digital camera is a device that allows you to receive images of objects in digital form. By and large, the difference between a conventional and a digital camera is only in the image receiver. In the first case, this is a photographic emulsion, which then requires chemical treatment. In the second - a special electronic sensor that converts the incident light into an electrical signal. This sensor is called a sensor or a matrix and really is a rectangular matrix of light-sensitive cells placed on a single semiconductor crystal.

When light hits a matrix element, it generates an electrical signal proportional to the amount of light that has fallen. Then the signals (so far these are analog signals) from the matrix elements are read and converted into digital form by an analog-to-digital (ADC) converter. Further, the digital data is processed by the camera's processor (yes, it also has a processor) and stored in the form of, in fact, a picture.

So, the heart of any digital camera is the sensor. Now there are two main technologies for the production of sensors - CCD (CCD, charge coupled device - charge coupled device) and CMOS. In the CCD-matrix during the exposure (that is, at the moment, in fact, photographing), a charge proportional to the intensity of the incident light accumulates in the photosensitive elements. When data is read, these charges are shifted from cell to cell until the entire matrix is ​​read (in fact, reading occurs line by line). This process in popular literature like to be compared with the transfer of buckets of water along the chain. CCD matrices are produced using MOS technology and, in order to obtain a high-quality image, they require high uniformity of parameters over the entire area of ​​the chip. Accordingly, they are quite expensive.

An alternative to CCDs are CMOS (that is, in Russian, CMOS) matrices. At its core, a CMOS sensor is quite similar to a random access memory chip - DRAM. Also a rectangular matrix, also capacitors, also a random access readout. Photodiodes are used as photosensitive elements in CMOS matrices. In general, CMOS sensors are much better suited for the production of today's well-developed manufacturing processes. In addition, among other things (higher packing density of elements, lower power consumption, lower price), this allows you to integrate related electronics onto a single chip with a matrix. True, until recently, CMOS could not compete with CCD in terms of quality, so, on the basis of CMOS sensors, mainly cheap devices like webcams were made. However, recently several large companies at once (in particular, such an industry monster as Kodak) have been developing technologies for the production of high-resolution and high-quality CMOS matrices. The first "serious" (three-megapixel digital SLR) CMOS camera - Canon EOS-D30 - appeared almost two years ago. And the Canon EOS 1Ds and Kodak Pro DCS-14n full-frame cameras, announced at the latest Photokina, finally demonstrated the potential of CMOS sensors. However, most cameras are still produced on the basis of CCD matrices.

Those who want to learn more about both technologies can start here www.eecg.toronto.edu/~kphang/ece1352f/papers/ng_CCD.pdf , and we'll go further.

The next moment - the elements of the matrix (any of the types described above) perceive only the intensity of the incident light (that is, they give a black and white image). Where does color come from? To obtain a color image, a special light filter is located between the lens and the matrix, consisting of primary color cells (GRGB or CMYG) located above the corresponding pixels. Moreover, two pixels are used for green (in RGB, or one in CMY), since the eye is most sensitive to this color. The final color of a pixel in the picture in such a system is calculated taking into account the intensities of neighboring elements of different colors, so that as a result, each single-color pixel of the matrix corresponds to a colored pixel in the picture. Thus, the final picture is always interpolated to some extent (that is, it is calculated, and not obtained by directly photographing the object, which inevitably affects the quality of the small details of the picture). As for specific filters, in most cases a rectangular matrix GRGB (Bayer filter) is used.

There is also such a thing as SuperCCD, invented by Fuji Photo Film and used in Fuji cameras since 2000. The essence of this technology is that the pixels (and the filter elements - also GRGB) are arranged in a kind of diagonal matrix.

Moreover, the camera interpolates not only the colors of the pixels themselves, but also the colors of the dots located between them. Thus, Fuji cameras always indicate a resolution that is twice the number of physical (single-color) pixels, which is not true. However, Fuji's technology still turned out to be quite successful - most people who compared the quality of images from SuperCCD and conventional cameras agree that the image quality from SuperCCD corresponds to a conventional matrix with a resolution about 1.5 times greater than the physical resolution of SuperCCD. But not 2 times as stated by Fuji.

Finishing the conversation about filters, it's time to mention the third alternative sensor technology, namely Foveon X3. It was developed by Foveon and was announced this spring. The essence of the technology is the physical reading of all three colors for each pixel (in theory, the resolution of such a sensor will be equivalent to the resolution of a conventional sensor with three times as many pixels). In this case, to divide the incident light into color components, the property of silicon (from which the sensor is made) is used to transmit light with different wavelengths (that is, color) to different depths. In fact, each Foveon pixel is a three-layer structure, and the depth of the active elements corresponds to the maximum light transmission of silicon for primary colors (RGB). I think it's a very promising idea. At least in theory. Because in practice, the first announced camera based on Foveon X3 remains the only one so far. And its deliveries have not really begun yet. We wrote more about this technology in the sixth issue of the newspaper this year.

But back to the sensors. The main characteristic of any matrix, from the point of view of the end user, is its resolution - that is, the number of photosensitive elements. Most cameras are now made on the basis of matrices of 2-4 megapixels (million pixels). Naturally, the higher the resolution of the matrix, the more detailed picture you can get on it. Of course, the larger the matrix, the more expensive it is. But you always have to pay for quality. The resolution of the matrix and the size of the resulting image in pixels are directly related, for example, on a megapixel camera we get a picture with a size of 1024x960 = 983040. It must be said that increasing the resolution of matrices is one of the main tasks that digital camera manufacturers are currently struggling with. Say, about three years ago, most mid-range cameras were equipped with megapixel matrices. Two years ago, this number increased to two megapixels. A year ago, it already became equal to three or four megapixels. Now, most of the latest camera models are equipped with sensors with a resolution of 4-5 megapixels. And there are already several semi-professional models equipped with matrices of more than 10 megapixels. Apparently, somewhere at this level, the race will stop, since a picture from a 10-megapixel matrix approximately corresponds in detail to a picture taken on a standard 35mm film.

By the way, do not confuse the resolution of the matrix in the form in which we defined it above, and the resolution. The latter is defined as the ability of a camera to separate an image of two objects, and is usually measured from a snapshot of a streak target with a known distance between streaks. Resolution describes the properties of the entire optical system of the camera - that is, the sensor and the lens. In principle, resolution and resolution are related, but this connection is determined not only by the parameters of the matrix, but also by the quality of the optics used in the camera.

The next characteristic of a digital camera, directly related to the matrix, is sensitivity. Or, more precisely, light sensitivity. This parameter, as the name implies, describes the sensitivity of the matrix to incident light and, in principle, is completely analogous to the sensitivity of conventional photographic materials. For example, you can buy 100, 200, or 400 speed film at the store. In the same way, you can set the sensitivity of the matrix, but the advantage of a digital camera is that the sensitivity is set individually for each frame. Say, in bright sunlight, you can shoot with a sensitivity of 100 or 50, and for night shooting you can switch to 400 (and in some cameras even to 1400). Most digital cameras allow you to set standard sensitivity values ​​​​- 50, 100, 200 and 400. In addition, the auto exposure system can change the sensitivity smoothly. Since the sensitivity is physically adjusted by changing the signal gain from the matrix, this is quite simple to implement in the camera.

Sensitivity is measured in ISO units (at least for digital cameras, they have already become the standard). You can see how they are converted to DIN and GOST units in the table.

However, adjustable sensitivity has its drawbacks. Since the properties of the matrix do not change physically, but simply amplify the existing signal, the image begins to show more and more noise inherent in any electronic device. This greatly reduces the working dynamic range of the camera, so at high sensitivity you will not get a good picture. A similar problem, by the way, can also be encountered at large exposures - any matrix makes noise, and over time, noise accumulates. Many cameras now implement special noise reduction algorithms for long exposures, but they tend to smooth the image and blur fine details. In general, you can’t argue against the laws of physics, but still the ability to adjust sensitivity is a big plus for digital cameras.

Konstantin AFANASIEV

Digital television is modern technology television broadcasting, which consists in the transmission of television sound and images using video coding. The television familiar to all of us is called analog and it is gradually becoming history. Its main disadvantage is the instability of the signal in various interferences and the ability to view only a few television channels. The digital signal is anti-interference, so it provides high quality sound and picture. In addition, on the same frequency, instead of an analog channel, it can transmit several digital ones at once. Thus, viewers get the opportunity to watch a variety of channels: general format, entertainment, information, educational, children's, music, sports, broadcasting series and movies.

Benefits of Digital TV

According to the transmission method, digital television is divided into:

1. terrestrial television broadcasting in DVB-T2 and DVB-T modes;
2. satellite and cable TV.

Advantages of digital TV connection:

• reducing the power of transmitters;
• increasing the noise immunity of television signals;
• improving the quality of picture and sound in TV receivers;
• a significant increase in TV programs;
• availability of interactive TV systems;
• Availability additional features: "video on demand", "transmission recording", "to the beginning of the transmission", subtitle and language selection;
• the ability to create an archive of programs, etc.

The antennas that are used to receive the signal also differ. When buying them, you need to take into account the range of the transmitting station, the conditions of direct visibility to the station, as well as the level of the transmitted signal. Thus, antennas with a suspension height of ten meters and a high gain are considered effective, as well as indoor antennas. But usually the reception of the signal is successfully carried out on the antenna that the subscriber has been using for a long time.

So, if the issue with buying a set-top box and installing a decimeter antenna is resolved, then you can start connecting the "numbers" to your TV. To do this, connect the tuner to the TV according to the instructions that come with it. Then we connect an antenna to it and use the remote control to start the channel search procedure. The search can be carried out manually or in automatic mode (choose the one that suits you). After a few minutes, the result will appear on the screen. Note that it is quite simple to find out if your TV supports digital television. So, if it has the designation DVB-T2, then it receives terrestrial digital television; if DVB-S - then it receives satellite TV and DVB-C - cable.

Before installing digital television, be sure to find out where the transmitting signal tower is located. In her direction, you will need to direct the antenna. If an external antenna is used, then it must be securely mounted on the brackets.

Many, many years ago, while working as an administrator at one of the city-forming enterprises of the Russian outback, I had to first encounter the concept of " digital signature"(hereinafter EDS).
At that time, the idea was rooted in the heads of the management that the EDS is a regular signature, scanned and added to all documents that must be “signed”.

Let's take a look at what EDS is and how it works.

To work with EDS, we first of all need digital certificate and private key.

First, we need to set the EDS under the document.
The installation of the EDS takes place in two steps:
1. We take the document that we want to sign and calculate the hash from this document. (Simplistically, a hash is a one-way mathematical function for converting an arbitrary-length document into a fixed-length document.)
2. Then, this received hash is encrypted with our private key.

Now the document, with the EDS attached to it and our certificate, is sent to the recipients.

Having received the signed document, we need to check the signature - is it valid or not.
Verification of the EDS is somewhat more complicated:
1. We take the document whose signature needs to be verified, calculate the hash from this document.
2. We take the digital certificate of the user who signed the document and the EDS attached to the document (which is the hash of the original document encrypted on the signer's private key) and decrypt it using the public key.
Thus, we have two hashes - the one that we calculated ourselves and the one that we received along with the document and decrypted with the signer's public key.
3. Now we compare these hashes. If the hashes match, then the signature is valid; if the hashes differ, then the signature is invalid.

In conclusion, let's define what the use of a digital signature gives us:
1. Immutability during transmission or storage - if the document has been changed, then the hash that we calculate and that was attached to the document will be different, therefore, the signature will be invalid, from which we can conclude that the document has been changed;
2. Non-repudiation of authorship - if the signature is correct, then the signer, the certificate (more precisely public key from the certificate) which is used to decrypt the hash and is the author of the document;

In order to make it impossible to forge an EDS, the private key must be in a single copy and only the owner must have access to it. This can be done using smart cards, but that's another story.