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For complete control over the process of obtaining a digital image, it is necessary at least in general terms to understand the structure and principle of operation of a digital camera.
The only fundamental difference between a digital camera and a film camera is the nature of the light-sensitive material used in them. If in a film camera it is a film, then in a digital camera it is a photosensitive matrix. And just as the traditional photographic process is inseparable from the properties of the film, so the digital photo process largely depends on how the matrix converts the light focused on it by the lens into a digital code.
The principle of the photomatrix
A light-sensitive matrix or photosensor is an integrated microcircuit (in other words, a silicon plate), consisting of the smallest light-sensitive elements - photodiodes.
There are two main types of sensors: CCD (Charge-Coupled Device, aka CCD - Charge-Coupled Device) and CMOS (Complementary Metal-Oxide-Semiconductor). Matrices of both types convert the energy of photons into an electrical signal, which is then subject to digitization, but if, in the case of a CCD matrix, the signal generated by the photodiodes enters the camera processor in analog form and only then is centrally digitized, then in the CMOS matrix each photodiode is equipped with an individual analog digital converter (ADC), and the data is sent to the processor in a discrete form. In general, the differences between CMOS and CCD sensors, although fundamental for an engineer, are absolutely insignificant for a photographer. For manufacturers of photographic equipment, it is also important that CMOS matrices, being more complicated and more expensive than CCD matrices in development, are more profitable than the latter in mass production. So the future is most likely in CMOS technology for purely economic reasons.
Photodiodes, which make up any matrix, have the ability to convert the energy of the luminous flux into an electric charge. The more photons the photodiode captures, the more electrons are produced at the output. Obviously, the larger the total area of \u200b\u200ball photodiodes, the more light they can perceive and the higher the light sensitivity of the matrix.
Unfortunately, photodiodes cannot be located close to each other, since then there would be no room on the matrix for the electronics accompanying the photodiodes (which is especially important for CMOS matrices). The light-sensitive surface of the sensor is on average 25-50% of its total area. To reduce light losses, each photodiode is covered with a microlens that exceeds it in area and is actually in contact with the microlenses of neighboring photodiodes. Microlenses collect light incident on them and direct it inside the photodiodes, thus increasing the light sensitivity of the sensor.
At the end of the exposure, the electric charge generated by each photodiode is read out, amplified and, by means of an analog-to-digital converter, converted into a binary code of a given width, which is then fed to the camera processor for further processing. Each photodiode of the matrix corresponds (though not always) one pixel of the future image.
Thanks for attention!
Vasily A.
Post scriptum
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Modern cameras do everything themselves - to get a picture, the user just needs to press a button. But it's still interesting: by what magic does the picture get into the camera? We will try to explain the basic principles of digital cameras.
Educational program: how a digital camera works
Main parts Anti-distortion
Main parts
Basically, the digital camera device repeats the analog design. Their main difference is in the photosensitive element on which the image is formed: in analog cameras it is a film, in digital cameras it is a matrix. Light through the lens enters the matrix, where a picture is formed, which is then written into memory. Now let's take a closer look at these processes.
The camera consists of two main parts - the body and the lens. The body contains a matrix, a shutter (mechanical or electronic, and sometimes both at once), a processor and controls. A lens, removable or built-in, is a group of lenses housed in a plastic or metal housing.
Where does the picture come from
The matrix consists of many light-sensitive cells - pixels. Each cell, when light hits it, generates an electrical signal proportional to the intensity of the light flux. Since information is used only about the brightness of the light, the picture is black and white, and in order for it to be colored, you have to resort to various tricks. The cells are covered with color filters - in most matrices, each pixel is covered with a red, blue or green filter (only one!) In accordance with the well-known RGB (red-green-blue) color scheme. Why these colors? Because they are basic, and all the rest are obtained by mixing them and decreasing or increasing their saturation.
On the matrix, the filters are arranged in groups of four, so for two greens there is one blue and one red. This is done because the human eye is most sensitive to green. Light rays of different spectrum have different wavelengths, so the filter lets only rays of its own color into the cell. The resulting picture consists of only red, blue and green pixels - this is how RAW files (raw format) are recorded. To record JPEG and TIFF files, the camera's processor analyzes the color values \u200b\u200bof adjacent cells and calculates the color of the pixels. This processing process is called color interpolation and is extremely important for producing high-quality photographs.
This arrangement of filters on the cells of the matrix is \u200b\u200bcalled the Bayer pattern.
There are two main types of matrices, and they differ in the way of reading information from the sensor. In CCD matrices, information is read from the cells sequentially, so file processing can take quite a long time. Although these sensors are "thoughtful", they are relatively cheap, and moreover, the noise level in the images taken with them is less.
CCD type sensor
In matrices like CMOS (CMOS) information is read individually from each cell. Each pixel is labeled with coordinates, which allows the sensor to be used for metering and autofocus.
CMOS sensor
The described types of matrices are single-layer, but there are also three-layer ones, where each cell perceives three colors at the same time, distinguishing differently colored color streams along the wavelength.
Three-layer matrix
The camera processor has already been mentioned above - it is responsible for all the processes that result in a picture. The processor determines the exposure parameters, decides which of them should be applied in a given situation. Photo quality and camera speed depend on the processor and software.
On the click of the shutter
The shutter measures the amount of time the light strikes the sensor (shutter speed). In the overwhelming majority of cases, this time is measured in fractions of a second - as they say, and you won't have time to blink. In digital SLR cameras, as in film cameras, the shutter consists of two opaque curtains that cover the sensor. Because of these shutters in digital SLRs, sighting on the display is impossible - after all, the matrix is \u200b\u200bclosed and cannot transmit an image to the display.
In compact cameras, the matrix is \u200b\u200bnot covered by the shutter, and therefore you can compose the frame on the display
When the shutter button is pressed, the curtains are set in motion by springs or electromagnets, light is available, and an image is formed on the sensor - this is how a mechanical shutter works. But digital cameras also have electronic shutters - they are used in compact cameras. An electronic shutter, unlike a mechanical one, cannot be touched by hands, it is, in general, virtual. The matrix of compact cameras is always open (this is why you can compose the frame by looking at the display, and not through the viewfinder), when the shutter button is pressed, the frame is exposed for the specified exposure time, and then recorded into memory. Due to the fact that electronic shutters do not have curtains, their shutter speeds can be ultra-short.
Let's get the focus
As mentioned above, the sensor itself is often used for autofocusing. In general, autofocus is of two types - active and passive.
For active autofocus, the camera requires a transmitter and receiver that work in the infrared region or with ultrasound. The ultrasound system measures the distance to an object using the echo-location method. Passive focusing is carried out using the contrast assessment method. Some professional cameras combine both focusing types.
In principle, the entire area of \u200b\u200bthe matrix can be used for focusing, and this allows manufacturers to place dozens of focusing zones on it, as well as use a "floating" focus point, which the user himself can place wherever he wants.
Anti-distortion
It is the lens that forms the image on the matrix. A lens consists of several lenses - three or more. A single lens cannot create a perfect image - it will distort at the edges (this is called aberration). Roughly speaking, the light beam should go directly to the sensor without scattering along the way. To some extent, this is facilitated by the diaphragm - a round plate with a hole in the middle, consisting of several blades. But you cannot close the aperture too much - because of this, the amount of light falling on the sensor decreases (which is used to determine the desired exposure). If you collect several lenses with different characteristics in succession, the distortions given by them together will be much less than the aberrations of each of them separately. The more lenses, the less aberration and the less light hits the sensor. After all, glass, no matter how transparent it may seem to us, does not let all the light through - some part is scattered, something is reflected. In order for the lenses to transmit as much light as possible, a special antireflection coating is applied to them. If you look at the camera lens, you will see that the surface of the lens shimmers with a rainbow - this is the antireflection coating.
The lenses are positioned inside the lens in something like this
One of the characteristics of a lens is aperture, the value of the maximum open aperture. It is indicated on the lens, for example, like this: 28/2, where 28 is the focal length, and 2 is the aperture. For a zoom lens, the marking looks like this: 14-45 / 3.5-5.8. Two apertures are indicated for zooms because they have different minimum apertures in wide and telephoto. That is, at different focal lengths the aperture ratio will be different.
The focal length, which is indicated on all lenses, is the distance from the front lens to the light receiver (in this case, the matrix). The angle of view of the lens and its, so to speak, range, that is, how far it "sees" depends on the focal length. Wide-angle lenses move the image away from our normal vision, while telephoto lenses zoom in and have a small angle of view.
The angle of view of the lens depends not only on its focal length, but also on the diagonal of the light receiver. For 35 mm film cameras, a lens with a focal length of 50 mm is considered normal (that is, approximately corresponding to the angle of view of the human eye). Lenses with a shorter focal length are "wide-angle", with a larger one - "telephoto".
The left part of the bottom inscription on the lens is the focal length of the zoom, the right part is the aperture
This is where the problem lies, because of which next to the focal length of a digital camera lens, its equivalent for 35 mm is often indicated. The diagonal of the matrix is \u200b\u200bless than the diagonal of 35 mm of the frame, and therefore it is necessary to "translate" the numbers into a more familiar equivalent. Due to the same increase in focal length in SLR cameras with "film" lenses, wide-angle shooting becomes almost impossible. A lens with a focal length of 18 mm for a film camera is super wide-angle, but for a digital camera its equivalent focal length will be about 30 mm or even more. As for telephoto lenses, the increase in their "range" is only in the hands of photographers, because a conventional lens with a focal length of, say, 400 mm, is quite expensive.
Viewfinder
In film cameras, you can only compose a shot using the viewfinder. Digital ones allow you to completely forget about it, since in most models it is more convenient to use the display for this. Some very compact cameras do not have a viewfinder at all, simply because there is no room for it.
The most important thing about a viewfinder is what you can see through it. For example, SLR cameras are called so precisely because of the design features of the viewfinder. The image is transmitted through the lens through a system of mirrors to the viewfinder, and thus the photographer sees the real area of \u200b\u200bthe frame. During shooting, when the shutter opens, the covering mirror rises and lets light through to the sensitive sensor. Such designs, of course, do an excellent job of their tasks, but they take up quite a lot of space and therefore are completely inapplicable in compact cameras.
This is how the image goes through the mirror system into the viewfinder of the SLR camera.
In compact cameras, real-vision optical viewfinders are used. This is, roughly speaking, a through hole in the camera body. Such a viewfinder does not take up much space, but its view does not correspond to what the lens “sees”.
There are also pseudo-mirror cameras with electronic viewfinders. In such viewfinders, a small display is installed, the image to which is transmitted directly from the matrix - in the same way as to an external display.
Flash
A flash, a pulsed light source, is known to be used to illuminate where the main lighting is insufficient. Built-in flashes are usually not very powerful, but they have enough flash to illuminate the foreground. On semi-professional and professional cameras there is also a contact for connecting a much more powerful external flash, it is called a "hot shoe".
These are, in general, the basic elements and principles of a digital camera. Agree, when you know how the device works, it is easier to achieve a quality result.
Electronic digital signatures are now common knowledge - many modern companies are slowly switching to electronic document management. And in everyday life, you probably came across this thing. In a nutshell, the essence of an EDS is very simple: there is a certification center, there is a key generator, a little more magic, and voila - all documents are signed. It remains to figure out what kind of magic allows a digital signature to work.
Roadmap
This is the fifth lesson in the Crypt Dive series. All lessons of the cycle in chronological order:
1. Key generation
The reason why RSA is strong is the difficulty of factoring large numbers. In other words, it is very difficult to brute force to find such primes that give the modulus n in the product. Keys are generated in the same way for signature and encryption.
When the keys are generated, you can start calculating the electronic signature.
2. Calculation of the electronic signature
3. Verification of electronic signature
RSA, as you know, is about to retire because computing power is growing by leaps and bounds. The day is not far off when a 1024-bit RSA key can be found in minutes. However, we will talk about quantum computers next time.
In general, you should not rely on the strength of this RSA signature scheme, especially with "cryptographically strong" keys like in our example.
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Abilify MyCite comes with an adhesive sensor (see bottom left of this image) and a smartphone.
A new digital tablet can tell doctors if a patient has taken their medication. The pill sends a signal to the wearable sensor when the patient is taking the medication, and this information is then sent to the doctor's office.
The whole system is called Abilify MyCite and consists of a tablet, wearable sensor and a smartphone app. The actual drug is Abilify (aripiprazole), a drug used to treat schizophrenia and bipolar disorder. The drug is marketed by Otsuka Pharmaceutical, and the sensor-in-tablet was developed by Proteus Digital Health.
How does the system work?
While the idea may sound like something of a science fiction movie, the technology is based on a principle first described over 200 years ago, said Dr. George Savage, chief medical officer and co-founder of Proteus Digital Health.
In 1800, Alessandro Volta invented a battery consisting of two dissimilar metals (zinc and copper) in a solution of sulfuric acid and brine. Batteries are made in a similar way to this day.
The system embedded in the pill is believed to be a sensor consisting of a silicon chip with a logic circuit and two pieces of metal: copper and magnesium. When the sensor falls into a solution of water or any other liquid that has polar molecules (such as hydrochloric acid in the stomach, which dissolves the pill, leaving the sensor behind), the device will generate a current. The current is very small, but it is enough to start the chip.
“Technically, this is a partial power source,” Savage said. "The patient becomes a battery."
Once activated, the chip - only 1 millimeter on the side and 0.3 mm thick - sends a very simple signal that encodes just one number. This number identifies the pill and tells the wearable, adhesive sensor that it has entered the body.
The tablet signal is not a radio signal. The logic circuit of the chip gives a small modulated current - the graph of the current levels will look like a sine wave. Since the human body is conductive, a wearable sensor can pick up changes. The modulated current can encode ones and zeros similar to an FM signal.
It works in the same way as an electrocardiogram. These machines pick up changes in electrical current in the body to control the heart rate. The wearable sensor does the same, although the current is less.
The tablet is designed to work for only about 3 minutes. This is enough time to send a signal to the wearable sensor to wake up and start collecting data. This saves battery power, Savage said, and allows the wearable sensor to work for a week at a time.
From patient to doctor
A wearable adhesive sensor can tell how active a patient is, said Bob McQuide, chief strategist at Otsuka Pharmaceutical. He can also check if the person taking the pills is lying down.
From the portable sensor, information that the patient has taken the pill is sent to the smartphone app via Bluetooth. The app then asks the patient how he is feeling and records the response. If the patient agrees, the app can send the time they took the pill, activity level and stress to the doctor, who can look at the data over time and get an idea of \u200b\u200bhow the patient is being treated. For example, the doctor may know if the patient always takes the medication at the same time of day, or if there is a tendency to forget and take the pill from time to time.
The information sent from the portable sensor to the phone and from the phone app to the doctor's office is encrypted and there is no realistic way to hack the signal without being in very close contact with the patient.
Even if the data allows doctors to ensure that patients are taking medication, there is no evidence that the system is improving adherence.
“These experiments have not been done yet,” McQuide said. However, such data could help doctors talk to patients about medication use and possibly identify good habits, he said.
Regimen compliance and proper use are an ongoing challenge. For example, many people who have missed a day's medicine, whatever it is, will take two pills the next day, although this cannot be done with some medicines. "People do what makes sense at work, for example, you skip the day, you come and do more work, but not in pharmacology."
After the transition of over-the-air broadcasting from analog to digital, it became necessary to purchase special devices for old TVs. All modern TV receiver models are equipped with a corresponding tuner. However, not everyone is ready to change their TV because of this. Knowing how a digital 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 the 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. There are a large number of models on sale that differ in cost and functionality. Among the main functions performed by the attachment, you can note:
- Plays multimedia files from a USB flash drive.
- Recording of TV broadcasts in ts format to an external drive.
- Ability to stop live view.
- Thanks to the TimeShift function, the broadcast of the TV program can be postponed.
Some budget modern TV models have significantly less functionality, although they are equipped with a DVB-T2 tuner. In such a situation, the console will be able to significantly expand its capabilities.
It should also be said about another type of tuner - Smart TV set-top boxes. They provide users with even more options.
These devices can work in one of two ways:
- All files are stored on a built-in medium; to run the necessary software, you must first install it.
- Cloud services are used to store working information, 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 connectors for connecting memory cards at once, and support a large number of multimedia formats.
Criterias of choice
It should be admitted that a digital TV set-top box is not the most complex consumer electronic device.
But even considering the relatively low cost of these devices, it is necessary to make the 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 in Russia the DVB-T2 digital television standard is used, 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.
Also, two more standards should be noted - DVB-S and DVB-S2. They are used to broadcast satellite TV. 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.
Many cable TV providers today use the DVB-C standard... This gives them the ability to encode the signal. Special modules are required to access it. If the device will be used to receive cable television, then it must support this standard as well.
Connection methods
If the tuner is purchased to work with an old TV, then it must contain three cinch or RCA connectors... One of them is used to output video signal, and the other two transmit audio in stereo. Most STB models today are equipped with an HDMI connector. It is a modern standard used for the simultaneous transmission of video and audio signals.
The presence of USB ports means that the device can be used as a multimedia player. In addition, an external drive is connected to them for recording TV programs, if this function is supported by the set-top box.
It is also worth paying attention to the through 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 not only capable of receiving a signal of the required standard, it is worth getting to know their useful functions. One of them is TimeShift (deferred view). Thanks to her, you can pause the broadcast of a TV program and not miss an interesting moment.
Also pay attention to the Personal Video Recorder (PVR) option. With its help, you can record programs if it is not possible to watch them live. It is quite obvious that for this external storage required... Many modern STB models can be used as a multimedia player due to the support of popular formats. The TV Guide function allows you to check the weekly program schedule for all available channels.
Popular consoles
You can find a large number of set-top boxes in retail chains, but it is sometimes quite difficult to give preference to one model or another, even if you know the selection criteria. Having got acquainted with an overview of popular consoles, it will be easier to make a decision.
Supra SDT-94
The device looks stylish and has a low cost.
The set-top box 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 customization.
- The presence of the HDMI connector.
- Parental control function.
If we talk about the shortcomings, then most often users note that the IR receiver does not work very well.
To control the console, you literally have to aim at it with the remote control. It is also worth noting the jumps in the image when connected to a TV using RCA connectors.
Oriel 963 device
A distinctive feature of the model is ease of setup. The prefix will be quickly dealt with by people who know nothing about electronic household appliances. It is also worth noting that the console has an aluminum casing. 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 an external HDD. The device has a built-in media player that copes well with all popular formats. Do not forget about the deferred viewing function, which is sometimes extremely necessary.
The model has the following advantages:
- High sensitivity of IR receiver.
- Control buttons are located on the front panel.
- Allows you to record the desired TV programs.
- Has many connectors.
The device has only one drawback - not the most convenient menu. Otherwise, there are no complaints about the Oriel 963.
B-Color DC1302 device
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. The control buttons located on the front panel will make the work with the attachment 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 console from overheating during operation. Among the shortcomings, one can note only a relatively small length of the power cord, as well as a slightly slower channel switching.
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, since he is ready to limit himself only to 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.
