Comparison of cmos and ccd in video surveillance. CCD and CMOS sensors for digital photo and video cameras

Therefore, there will be no single focal point and the eye will not be able to see clearly images of objects.

The symptoms of astigmatism are not very specific; in the early stages, the disease often manifests itself as a slight blurred vision, therefore it is often mistaken for eye fatigue.

They differ from conventional ones in that they have a thicker surface, combining a spherical shape with a cylindrical one. The appointment of lenses is carried out by a specialist based on the diagnosis.

Hormones are involved in sexual development, control respiration, and are responsible for reproductive function and human sensory perception. Excess or lack of hormones impairs a person's quality of life.

Of course, this option has both contraindications and a minus in the form of price.

Desired form for obtaining a statement (e-mail)

injuries, or operations, or diseases, the correct shape of the cornea is disturbed.

Unlike myopia, astigmatism does not progress, so the correct and early selection of glasses or contact lenses can fully restore visual acuity for life.

FTC allows bringing the optical system of the eye to a higher degree of proportionality, which is reflected in the level of functioning of the visual analyzer as a whole.

How I got rid of astigmatism.

The brain cannot continue to process signals from the eye normally. Such a decrease in vision cannot be corrected with glasses.

By attaching spherical lenses, the refraction of this meridian is determined. Then the ophthalmologist rotates the slit 90 degrees, while the patient notes a deterioration in vision.

Thanks to such lenses, the refraction of rays in one meridian is changed, while the disadvantages of the changed optical system of the eyes are corrected.

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The simplest assessment option is the difference between the strongest and the weakest refraction.

During this time, the upper layer of the cornea is lifted, excess tissue is removed with the help of a laser, after which the break is fixed with collagen.

The curves obtained make it possible to judge the shape of the astigmatic focal surfaces, and on the basis of this, about some of the features of the system under study.

Try to avoid mechanical irritation of the eyes from cold, sun, wind with sand, etc.

To identify congenital astigmatism, it is necessary to carry out clinical examination of children in accordance with the age schedule.

CCD and CMOS sensors have been in constant competition for the past few years. In this article, we will try to consider the advantages and disadvantages of these technologies.

CCD (short for “charge coupled device”) or CCD matrix (abbreviated from the English. CCD, "Charge-Coupled Device") - a specialized analog integrated circuit consisting of photosensitive photodiodes, made on the basis of silicon, using the technology of CCD - devices with charge coupled.

In a CCD sensor, the light (charge) incident on the sensor pixel is transmitted from the microcircuit through one output node, or through just a few output nodes. The charges are converted to a voltage level, accumulated and sent out as an analog signal. This signal is then summed and converted to numbers by an analog-to-digital converter outside the sensor.

CMOS (complementary logic on metal-oxide-semiconductor transistors;
KMDP; English CMOS, Complementary-symmetry / metal-oxide semiconductor) is a technology for constructing electronic circuits.

In the early days, conventional CMOS chips were used for display, but picture quality was poor due to the low light sensitivity of CMOS elements. Modern CMOS sensors are manufactured using more specialized technology, which has led to a rapid increase in image quality and light sensitivity in recent years.

CMOS chips have several advantages. Unlike CCD sensors, CMOS sensors contain amplifiers and analog-to-digital converters, which significantly reduces the cost of the final product, because it already contains all the necessary elements to obtain the image. Each CMOS pixel contains electronic converters. CMOS sensors have more functionality and wider integration capabilities.

One of the main problems when using CMOS matrices the video cameras had image quality. CCD matrices have provided and are now providing a lower noise level. As a result CMOS chips behaved extremely poorly in low light compared to CCD chips... And since low light is one of the main difficulties in filming, it was a major barrier to use. CMOS matrices... However, the manufacturing experience gained over the years of CMOS development has allowed with each new generation of these sensors to significantly reduce the fixed and random noise that affects the image quality.

Another weak point CMOS - distortions that appear when capturing a dynamic image due to poor sensor sensitivity. Car images may contain very bright elements such as headlights, the sun, or very dark areas such as on license plates. For this reason, a wide dynamic range is required to handle scenes with large contrast drops. The CCD sensor has good dynamic range parameters, but the CMOS access to individual pixels gives you much more opportunity to get a better dynamic range. Also, with CCDs, bright spots in the scene can create vertical lines in the picture and interfere with license plate recognition due to fading and blurring.

Despite the fact that CCDs have a higher sensitivity characteristic, the main factor limiting their use is the low rate of charge readout and, as a result, the inability to provide a high speed of image formation. The higher the matrix resolution, the slower the imaging speed. In turn, the CMOS technology, combining a photosensitive element and a processing microcircuit, allows obtaining a high frame rate even for 3 megapixel sensors.

However, the use of megapixel CMOS sensors for IP cameras in video surveillance systems requires efficient compression of the data stream. The most common IP CCTV compression algorithms currently are M-JPEG, MPEG4 and H.264. The first is often implemented directly on the CMOS sensor by the matrix manufacturer itself. MPEG4 and H.264 algorithms are more efficient, but require a powerful processor. To form a real-time stream with a resolution of more than 2 megapixels, CMOS IP cameras use coprocessors that provide additional calculations.

Currently, IP cameras based on CMOS sensors are becoming more and more popular, primarily due to the technology support from the leaders of IP video surveillance. At the same time, their cost is higher than similar cameras on CCD. This is despite the fact that CMOS technology, combining the analog and digital parts of the device, allows you to create cheaper cameras. The situation is such that today the cost of an IP camera is determined by its capabilities and characteristics. The main thing is not the type of matrix, but the software implemented by the camera processor.

Advantages of CCD matrices:

• Low noise level.
• High pixel fill factor (about 100%).
• High efficiency (the ratio of the number of registered photons to their total number hitting the light-sensitive area of \u200b\u200bthe matrix, for CCD - 95%).
• High dynamic range (sensitivity).
• Good IR sensitivity.

• The complex principle of reading the signal, and therefore the technology.
• High level of power consumption (up to 2-5W).
• More expensive to manufacture.

• High performance (up to 500 frames / s).
• Low power consumption (almost 100 times compared to CCD).
• Cheaper and easier to manufacture.
• Prospects of the technology (in principle, it costs nothing to implement all the necessary additional circuits on the same crystal: analog-to-digital converters, processor, memory, thus obtaining a complete digital camera on one crystal).

• Low pixel fill factor, which reduces sensitivity (effective pixel surface ~ 75%, the rest is occupied by transistors).
• A high noise level (it is due to the so-called tempo currents - even in the absence of illumination, a rather significant current flows through the photodiode), the fight against which complicates and increases the cost of the technology.
• Low dynamic range.

Like any technology, CMOS and CCD technologies have advantages and disadvantages, which we have tried to consider in this article. Both technologies are used in the production of sensors for VeSta cameras. Both digital and analog VeSta cameras are manufactured on the basis of CMOS and CCD sensors. VeSta analog cameras are mainly manufactured on the basis of CCD sensors. VeSta analog cameras based on CMOS sensors are marked with the “C” symbol, for example, VC-200c. VeSta IP cameras mainly use CMOS sensors, but there are also cameras based on CCD matrices, for example, VC-6304 IR, created on the basis of a CCD sensor capable of generating video images with a resolution of up to 928 * 576 (960H). When choosing VeSta cameras, it is necessary to take into account all the pros and cons of these technologies, paying attention to such parameters as light sensitivity, wide dynamic range, power consumption, noise level, and cost of the camera.

With insulated gate with channels of different conductivity.

Benefits

• The main advantage of CMOS technology is its low static power consumption. This makes it possible to use such matrices as part of non-volatile devices, for example, in motion sensors and surveillance systems, which are in the "sleep" or "event waiting" mode most of the time.
• An important advantage of the CMOS matrix is \u200b\u200bthe unity of the technology with the rest, digital elements of the equipment. This leads to the possibility of combining analog, digital and processing parts on one crystal (CMOS technology, being primarily a processor technology, implies not only the "capture" of light, but also the process of converting, processing, cleaning signals not only actually captured, but and third-party components of CEA), which served as the basis for miniaturization of cameras for a wide variety of equipment and reducing their cost due to the rejection of additional processor chips.
• The random access mechanism can read selected groups of pixels. This operation is called cropped reading (eng. windowing readout). Cropping allows you to reduce the size of the captured image and potentially increase the read speed compared to CCD sensors, since in the latter, all information must be unloaded for further processing. It becomes possible to use the same matrix in fundamentally different modes. In particular, by quickly reading only a small part of the pixels, it is possible to provide a high-quality live image viewing mode on the screen built into the device with a relatively small number of pixels. You can scan only part of the frame and apply it to full screen display. Thus, to get the opportunity to high-quality manual focusing. It is possible to conduct reportage high-speed shooting with a smaller frame size and resolution.
• In addition to the amplifier within the pixel, amplification circuits can be placed anywhere along the signal path. This allows you to create amplification stages and increase sensitivity in low light conditions. The ability to change the gain for each color improves, in particular, the white balance.
• Low cost of production in comparison with CCD matrices, especially with large matrix sizes.

disadvantages

• The photodiode of the cell occupies a significantly smaller area of \u200b\u200bthe matrix element compared to a full-frame transfer CCD. Therefore, early CMOS sensors had significantly lower light sensitivity than CCDs. But in 2007, Sony launched a new line of new-generation CMOS video and cameras with EXMOR technology, which was previously only used for CMOS sensors in specific optical devices such as electron telescopes. In these matrices, the electronic "binding" of the pixel, preventing the advancement of photons to the light-sensitive element, was moved from the upper to the lower layer of the matrix, which made it possible to increase both the physical size of the pixel with the same geometric dimensions of the matrix, and the accessibility of the elements to light, which, accordingly, increased light sensitivity of each pixel and the matrix as a whole. For the first time, CMOS matrices were compared with CCD matrices in terms of light sensitivity, but they turned out to be more energy-saving and devoid of the main drawback of CCD technology - the "fear" of point light. In 2009, Sony improved EXMOR CMOS sensors with "Backlight illumination" technology. The idea of \u200b\u200bthe technology is simple and fully corresponds to the name.
• The photodiode of the matrix cell has a relatively small size, while the value of the resulting output voltage depends not only on the parameters of the photodiode itself, but also on the properties of each pixel element. Thus, each pixel of the matrix turns out to have its own characteristic curve, and the problem of the spread of light sensitivity and contrast ratio of the matrix pixels arises. As a result, the first manufactured CMOS matrices had a relatively low resolution and a high level of the so-called "structured noise" (eng. pattern noise).
• The presence on the matrix of a large volume of electronic elements in comparison with the photodiode creates additional heating of the device during the reading process and leads to an increase in thermal noise.

see also

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Matrix (sensor) - A photosensitive element of a camera, consisting of pixel cells that convert light into an electrical signal. The main types of matrices: CCD (CCD) and CMOS (CMOS), differing in the way information is read from the cells. The CCD has the best ... ... Glossary of Samsung Home and Computer Terms

Matrix on a printed circuit board of a digital camera Matrix or photosensitive matrix is \u200b\u200ba specialized analog or digital-analog integrated microcircuit consisting of photosensitive elements of photodiodes. Designed for ... ... Wikipedia

The matrix is \u200b\u200bthe foundation of any photo or video device. It determines the quality and size of the resulting image. Today in the manufacture of matrices, two different technological principles are used - CCD and CMOS. One often hears the question: "Which matrix to choose: CCD or CMOS?" Among fans of photo and video equipment, there are heated debates about this. In this article, we will review these two types and try to figure out which matrix is \u200b\u200bbetter - CCD or CMOS.

general information

Matrices are designed to digitize the parameters of light rays on their surface. It is not possible to speak about the clear advantage of one of the technologies. Comparisons can be made according to specific parameters and a leader can be identified in one aspect or another. As for the preferences of users, often the main criterion for them is the cost of the product, even if it is inferior in quality or technical characteristics to its competitor.

So let's see what both types of devices are. A CCD-matrix is \u200b\u200ba microcircuit that consists of light-sensitive photodiodes; it is silicon-based. The peculiarity of its work lies in the principle of operation of a charge-coupled device. CMOS-matrix is \u200b\u200ba device based on a semiconductor device with an insulated gate with channels of different conductivity.

Principle of operation

Let's move on to identifying the differences that will help determine the choice: which is better - a CMOS matrix or a CCD? The main difference between these two technologies is how they work. CCD devices convert the charge from the pixels into an electrical potential, which is amplified outside the photosensitive sensors. The result is an analog image. After that, the entire picture is digitized in the ADC. That is, the device consists of two parts - the matrix itself and the transducer. CMOS technology is characterized by the fact that it digitizes each pixel separately. The output is a ready-made digital picture. That is, the electric charge in the matrix pixel is accumulated in the capacitor, from which the electric potential is removed. It is transmitted to an analog amplifier (built directly into the pixel), after which it is digitized in a converter.

Should you choose CCD or CMOS?

One of the important parameters that determine the choice between these technologies is the number of matrix amplifiers. CMOS devices have a larger number of these devices (at each point), therefore, when the signal passes through, the picture quality decreases slightly. Therefore, CCDs are used to create images with a high degree of detail, for example, in medical, research, and industrial purposes. But CMOS technologies are used mainly in household appliances: webcams, smartphones, tablets, laptops, etc.

The next parameter that determines which type is better - CCD or CMOS - is the density of the photodiodes. The higher it is, the fewer photons will “disappear”, respectively, the image will be better. In this parameter, CCD matrices bypass their competitors, since they offer a layout that does not have such gaps, while CMOS has them (transistors are located in them).

Nevertheless, when the user has a choice: which one - CMOS or CCD - to buy, the main parameter pops up - the price of the device. CCD technology is significantly more expensive than its competitor and more energy intensive. Therefore, it is impractical to install them where the image of average quality is sufficient.

A CMOS matrix is \u200b\u200ba device whose main function is to digitize certain parameters of light rays that hit its surface. In modern photo and video equipment, two matrix standards are used: CMOS and CCD. This article compares the two technologies.

general information

So, the CCD matrix. This type was initially considered the highest quality, but also more energy-consuming and expensive. such devices are based on collecting the entire picture in an analog version, followed by digitization. CMOS-matrix, unlike its competitor, digitizes each pixel separately.

Comparison of the two technologies

CMOS devices were initially less power-consuming and cheaper, especially when manufacturing large-sized devices, but they were inferior to CCDs in quality. To this day, CCD technologies are distinguished by a higher quality image, they are used in various fields of science and industry, where the highest requirements are imposed on the picture quality. For example, in medicine.

In recent years, this type of device has significantly reduced energy consumption and cost, but the CMOS matrix has significantly advanced in its development. For example, the image quality standard has been improved and brought to a new level. Moreover, a technological revolution was made in the production of sensors based on CMOS technology, namely: a transistor amplifier was introduced for reading each pixel of the image. This made it possible to convert charge into voltage directly at the point. Thanks to this, the CMOS matrix has become on a par with the CCD technology. And now most modern devices are based on a CMOS device.

Benefits of CMOS Technology

Summarizing the above, we can summarize the advantages of such devices. This is a low power consumption in a static mode, low cost of manufacturing (especially if you take into account the large, but the most important advantage is the ability to produce a finished one that does not require additional conversions.

The use of CMOS technologies in computer technology

Every user of modern computer equipment encounters a device such as a web camera every day. But few people know that it is based on the principle of CMOS technology.

Webcams are used both as separate functional devices and built-in ones, for example, in laptops. These devices are designed to work with networked multimedia applications. The above products include: lens, matrix, video capture card, optical filter, image compression unit, processor, flash memory, web server and network interface. The matrix is \u200b\u200bthe basis of any video camera or photo camera. Indeed, the quality of the transmitted image will depend on the resolution of this device. Usually this parameter in webcams is in the range from 0.1 to 2 megapixels. However, in most products it is 0.3 megapixels. Another indicator that defines a webcam is the frame format. The most popular is the 1/4 CMOS sensor. There are other formats, but they are less common (for example, 1/3, 1/2 or 2/3 inch).