When installing video surveillance at a site, the technician must take into account how illuminated the area is to which the camera will be directed. If the lens “looks” in the direction from which the light shines most of the day, a number of objects will be illuminated. That is, the operator will not be able to examine the details of everything that is happening in the protected area. This is one of the reasons why such a big role is given to planning the installation points of tracking devices.
Owners of regular cameras and phones also encounter flare. BLC function is an option that allows compensate for light exposure. With its help, all objects in the frame appear equally illuminated, although in fact this is not always true.
Why does flare occur?
A video camera is often compared to the human organ of vision - it also has its own clarity, light sensitivity, and perceives a certain number of frames per second. When we look at an object located between us and a bright source of light, it is not always possible to consider its details.
The reason for the flare lies in the fact that the individual pixels that make up the matrix are capable of receiving a certain maximum of light. If there is more of it, just a light spot will appear on the image displayed on the screen. However, even before the maximum is reached, a kind of saturation occurs. For example, the sun behind a person “loads” the matrix so much that its power becomes insufficient for a clear perception of other elements.
The pixels do not have time to accumulate sufficient charge, so in the best case, the photo of the object turns out to be less lit than it really is. This creates certain problems in security video surveillance:
It is not always possible to recognize a car's license plate number if the vehicle's headlights are on;
The bright light makes it difficult to see the face of the person who entered the territory;
It is difficult to see small details (labels on product boxes).
Appearance BLC technologies allowed us to partially get rid of these problems. It can be found in video cameras for custom shooting, and even in mobile phones.
Light compensation BLC
If we explain in simple words what it is (BLC), we succeeded, let’s talk about how this compensation works in practice. There are 3 options in total:
- The use of a shutter that would periodically close, cutting off the light source from the sensitive matrix. If it has been open for a short time, the likelihood of exposure is reduced.
The use of an aperture, which would narrow if the flow of light increases beyond a certain limit. This is what happens in the world of living beings - when there is insufficient lighting, the diaphragm opens as much as possible, and when there is excessive lighting, it narrows to the limit;
Automatic gain control - image pre-processing based on maximum illumination level settings. If they are exceeded in a particular area, it is artificially lowered. At the output (TV screen, monitor), the operator will see the already processed data;
We present to your attention a list of Symbols that are used in the SpyG video surveillance systems catalog when describing the technical characteristics of the equipment.
Description of technical characteristics of video surveillance systems:*
3D-DNR - video noise filtering algorithm is based on comparing adjacent frames, identifying video noise and neutralizing it (filtering). The main task of DNR is to obtain an image without video noise in low light conditions. In turn, a more complex, but also more efficient 3D-DNR algorithm has been created. Unlike previous versions of DNR, each frame is processed not once, but several times, which allows you to obtain a higher quality frame. I would also like to clarify that by reducing noise, the file size in the archive (when recording) is reduced. Savings can be up to 40% when using the JPEG algorithm and up to 70% when using the MPEG algorithm.
WDR (Wide Dynamic Range) mode) extended dynamic range. Thanks to this mode, the image received from the video camera looks more saturated and balanced in color characteristics. If the viewing area has bright and dark areas or the background is too bright, a camera with a WDR function would be the optimal solution for the subject being observed. Example of use: you are observing a person against a light background. Without any processing, you have a light “picture” and a dark outline of a person, as if you saw him against the background of the setting sun. Beautiful - yes, informative - no.
The next generation of processing is the so-called BLC (back light compensation). In this case, the video camera detects the illumination of the image and decides to compensate for it. As a result, we distinguish a person, but do not see what is happening behind him. When using a camera with WDR mode, you distinguish not only the person, but also what happens next. This is achieved by combining the same image taken in two different modes.
Customizable parameters and functions of OSD camerasand possible cases of their use:
1. Brightness, contrast, clarity, color, gamma correction - allows you to configure the parameters of the signal received from the camera; these settings will be an obvious advantage when connecting to “economy class” recorders (most often, equipment of this class allows you to set general parameters for all channels, without allowing individual adjustment of each channel).
2. Shutter speed modes (SHUTTER) - This parameter has automatic and manual modes; manual modes can be useful for shooting fast processes or, on the contrary, allow you to shoot slow processes in low light conditions.
3. Back Light Compensation (BLC)- also has automatic and manual modes; in manual mode, it allows you to select zones for processing. Zone-by-zone adjustment of this parameter is required in the case when there is simultaneously a source of oncoming light and an object that needs to be identified in the frame, a special case of reading a car license plate at night (the headlights and license plate are in the frame).
4. Gain Setting (AGC)- allows you to more accurately adjust the gain level.
5. White balance (WHITE BALANCE)- automatic control mode, automatic tracking mode and manual mode, allows you to improve image quality in difficult and special lighting conditions.
6. Service function “Camera name” (CAMERA ID)- allows you to assign each camera its own text identifier (for example, a camera number or a description of a meta setting) and set the area of its display in the frame. Possible applications in systems that do not include a recorder or where the recorder does not allow channel naming.
7. Day-Night function (DAY/NIGHT)- allows you to set automatic and manual operating modes. Manual setting allows you to forcefully set the mode to black and white or color. Automatic mode allows the camera to operate in black and white in low light conditions, which significantly reduces the level of noise that usually appears in color. For automatic mode, you can also configure operating conditions, for example, a time delay, this will eliminate false switches when the lens is briefly blocked.
8.Motion DET function- has a number of settings (selection of zone, sensitivity, etc.), mainly this function is aimed at increasing the efficiency of surveillance; if movement is detected, the camera issues an appropriate message, which attracts the operator’s attention and reduces reaction time.
9. Function “Setting up hidden areas” (PRIVACE)- allows you to electronically hide zones that are not desirable for monitoring the surveillance system, allows you to flexibly configure up to four zones.
* based on material from the site http://www.acecop.su
Vendors now offer a huge selection of video surveillance cameras. Models differ not only in parameters common to all cameras - focal length, viewing angle, light sensitivity, etc. - but also in various proprietary features that each manufacturer strives to equip their devices with.
Therefore, often a brief description of the characteristics of a video surveillance camera is a frightening list of incomprehensible terms, for example: 1/2.8" 2.4MP CMOS, 25/30fps, OSD Menu, DWDR, ICR, AWB, AGC, BLC, 3DNR, Smart IR, IP67, 0.05 Lux and that's not all.
In the previous article, we focused on video standards and the classification of cameras depending on them. Today we will analyze the main characteristics of video surveillance cameras and deciphering the symbols of special technologies used to improve the quality of the video signal:
- Focal length and viewing angle
- Aperture (F number) or lens aperture
- Adjusting the iris (auto iris)
- Electronic shutter (AES, shutter speed, shutter speed)
- Sensitivity (light sensitivity, minimum illumination)
- Protection classes IK (Vandal-proof, anti-vandal) and IP (from moisture and dust)
Matrix type (CCD CCD, CMOS CMOS)
There are 2 types of CCTV camera matrices: CCD (in Russian - CCD) and CMOS (in Russian - CMOS). They differ in both structure and principle of operation.
| CCD | CMOS |
| Sequential reading from all matrix cells | Random reading from matrix cells, which reduces the risk of smearing - the appearance of vertical smearing of point light sources (lamps, lanterns) |
| Low noise level | High noise level due to so-called tempo currents |
| High dynamic sensitivity (more suitable for shooting moving objects) | “Rolling shutter” effect - when shooting fast moving objects, horizontal stripes and image distortion may occur |
| The crystal is used only to accommodate photosensitive elements; the remaining microcircuits must be placed separately, which increases the size and cost of the camera | All chips can be placed on a single chip, making production of CMOS cameras simple and inexpensive |
| By using the matrix area only for photosensitive elements, the efficiency of its use increases - it approaches 100% | Low power consumption (almost 100 times less than CCD matrices) |
| Expensive and complex production | Performance |
For a long time it was believed that the CCD matrix produces much higher quality images than CMOS. However, modern CMOS matrices are often practically in no way inferior to CCDs, especially if the requirements for the video surveillance system are not too high.
Matrix size
Indicates the diagonal size of the matrix in inches and is written as a fraction: 1/3", 1/2", 1/4", etc.
It is generally believed that the larger the matrix size, the better: less noise, clearer picture, larger viewing angle. However, in fact, the best image quality is provided not by the size of the matrix, but by the size of its individual cell or pixel - the larger it is, the better. Therefore, when choosing a video surveillance camera, you need to consider the matrix size along with the number of pixels.
If matrices with sizes 1/3" and 1/4" have the same number of pixels, then in this case a 1/3" matrix will naturally give a better image. But if it has more pixels, then you need to pick up a calculator and calculate the approximate pixel size.
For example, from the matrix cell size calculations below, you can see that in many cases the pixel size on a 1/4" matrix turns out to be larger than on a 1/3" matrix, which means a video image with 1/4", although it is smaller in size, it will be better.
| Matrix size | Number of pixels (millions) | Cell size (µm) |
| 1/6 | 0.8 | 2,30 |
| 1/3 | 3,1 | 2,35 |
| 1/3,4 | 2,2 | 2,30 |
| 1/3,6 | 2,1 | 2,40 |
| 1/3,4 | 2,23 | 2,45 |
| 1/4 | 1,55 | 2,50 |
| 1 / 4,7 | 1,07 | 2,50 |
| 1/4 | 1,33 | 2,70 |
| 1/4 | 1,2 | 2,80 |
| 1/6 | 0,54 | 2,84 |
| 1 / 3,6 | 1,33 | 3,00 |
| 1/3,8 | 1,02 | 3,30 |
| 1/4 | 0,8 | 3,50 |
| 1/4 | 0,45 | 4,60 |
Focal length and viewing angle
These parameters are of great importance when choosing a video surveillance camera, and they are closely related to each other. In fact, the focal length of a lens (often denoted f) is the distance between the lens and the sensor.
In practice, the focal length determines the camera's viewing angle and range:
- the shorter the focal length, the wider the viewing angle and the less detail can be seen on objects located in the distance;
- The longer the focal length, the narrower the viewing angle of the video camera and the more detailed the image of distant objects.
If you need a general overview of a certain area, and you want to use as few cameras as possible for this, buy a camera with a short focal length and, accordingly, a wide viewing angle.
But in those areas where detailed observation of a relatively small area is required, it is better to install a camera with an increased focal length, pointing it at the object of observation. This is often used at the checkout counters of supermarkets and banks, where you need to see the denomination of banknotes and other payment details, as well as at the entrance to parking lots and other areas where it is necessary to distinguish a license plate number over a long distance.
The most common focal length is 3.6 mm. It roughly corresponds to the viewing angle of the human eye. Cameras with this focal length are used for video surveillance in small spaces.
The table below contains information and relationships between focal length, viewing angle, recognition distance, etc. for the most common focuses. The numbers are approximate, as they depend not only on the focal length, but also on other parameters of the camera optics.
Depending on the width of the viewing angle, video surveillance cameras are usually divided into:
- conventional (viewing angle 30°-70°);
- wide-angle (viewing angle from approximately 70°);
- long-focus (viewing angle less than 30°).
The letter F, only usually capitalized, also denotes the lens aperture - therefore, when reading the characteristics, pay attention to the context in which the parameter is used.
Lens type
Fixed (monofocal) lens- the simplest and most inexpensive. The focal length is fixed and cannot be changed.
IN varifocal (variofocal) lenses you can change the focal length. Its setting is done manually, usually once when the camera is installed at the shooting location, and then as needed.
Transfactor or zoom lenses They also provide the ability to change the focal length, but remotely, at any time. The focal length is changed using an electric drive, which is why they are also called motorized lenses.
"Fisheye" (fisheye, fisheye) or panoramic lens allows you to install just one camera and achieve a 360° view.
Of course, the resulting image has a “bubble” effect - straight lines are curved, but in most cases, cameras with such lenses allow you to divide one general panoramic image into several separate ones, with adjustments for the perception familiar to the human eye.
Pinhole lenses allow for covert video surveillance due to its miniature size. In fact, a pinhole camera does not have a lens, but only a miniature hole instead. In Ukraine, the use of covert video surveillance is seriously limited, as is the sale of devices for it.
These are the most common lens types. But if we go deeper, lenses are also divided according to other parameters:
Aperture (F number) or lens aperture
Determines the camera's ability to capture high-quality images in low-light conditions. The higher the F number, the less open the aperture and the more light the camera needs. The smaller the aperture, the wider the aperture is, and the camcorder can produce clear images even in low light.
The letter f (usually lowercase) also denotes the focal length, so when reading the characteristics, pay attention to the context in which the parameter is used. For example, in the picture above, the aperture is indicated by a small f.
Lens mount
There are 3 types of mounts for attaching a lens to a video camera: C, CS, M12.
- The C mount is rarely used anymore. C lenses can be mounted on a CS mount camera using a special ring.
- The CS mount is the most common type. CS lenses are not compatible with C cameras.
- The M12 mount is used for small lenses.
Iris adjustment (auto iris), ARD, ARD
The diaphragm is responsible for the flow of light onto the matrix: with an increased flow of light, it narrows, thus preventing the image from being overexposed, and in low light, on the contrary, it opens so that more light falls on the matrix.
There are two large groups of cameras: fixed aperture(this also includes cameras without it at all) and with adjustable.
The aperture can be adjusted in various models of video surveillance cameras:
- Manually.
- Automatically video camera using direct current, based on the amount of light hitting the sensor. This automatic iris adjustment (ADA) is referred to as DD (Direct Drive) or DD/DC.
- Automatically a special module built into the lens and tracking the light flux passing through the relative aperture. This method of ARD in the specifications of video cameras is designated as VD (Video Drive). It is effective even when direct sunlight hits the lens, but surveillance cameras with it are more expensive.
Electronic shutter (AES, shutter speed, shutter speed, shutter)
Different manufacturers may refer to this parameter as an automatic electronic shutter, shutter speed or shutter speed, but essentially it means the same thing - the time during which light is exposed to the matrix. It is usually expressed as 1/50-1/100000s.
The action of the electronic shutter is somewhat similar to automatic iris adjustment - it adjusts the light sensitivity of the matrix to adjust it to the light level of the room. In the picture below you can see the image quality in low light conditions at different shutter speeds (the picture shows the manual setting, while AES does it automatically).
Unlike ARD, adjustment occurs not by adjusting the light flux entering the matrix, but by adjusting the shutter speed, the duration of the accumulation of electrical charge on the matrix.
However the capabilities of the electronic shutter are much weaker than automatic iris adjustment, Therefore, in open spaces where the lighting level varies from twilight to bright sunlight, it is better to use cameras with ADS. Video cameras with an electronic shutter are optimal for rooms where the light level changes little over time.
The characteristics of the electronic shutter differ little between different models. A useful feature is the ability to manually adjust the shutter speed (shutter speed), since in low light conditions low values are automatically set, and this leads to blurred images of moving objects.
Sens-UP (or DSS)
This is a function of accumulating the charge of the matrix depending on the level of illumination, i.e. increasing its sensitivity at the expense of speed. Necessary for shooting high-quality images in low-light conditions, when tracking high-speed events is not critical (there are no fast-moving objects at the object of observation).
It is closely related to the shutter speed (shutter speed) described above. But if the shutter speed is expressed in time units, then Sens-UP is expressed in the shutter speed increase factor (xN): the charge accumulation time (shutter speed) increases by N times.
Permission
We touched on the topic of CCTV camera resolutions a little in the last article. Camera resolution is, in fact, the size of the resulting image. It is measured either in TVL (television lines) or in pixels. The higher the resolution, the more detail you will be able to see in the video.
Video camera resolution in TVL- this is the number of vertical lines (brightness transitions) placed horizontally in the picture. It is considered more accurate because it gives an idea of the size of the output image. While the resolution in megapixels indicated in the manufacturer's documentation can mislead the buyer - it often refers not to the size of the final image, but to the number of pixels on the matrix. In this case, you need to pay attention to such a parameter as “Effective number of pixels”
Resolution in pixels- this is the horizontal and vertical size of the picture (if it is specified as 1280x960) or the total number of pixels in the picture (if it is specified as 1 MP (megapixel), 2 MP, etc.). Actually, the resolution in megapixels is very simple to obtain: you need to multiply the number of horizontal pixels (1280) by the number of vertical pixels (960) and divide by 1,000,000. Total 1280×960 = 1.23 MP.
How to convert TVL to pixels and vice versa? There is no exact conversion formula. To determine the video resolution in TVL, you need to use special test tables for video cameras. For an approximate representation of the ratio, you can use the table:
Effective pixels
As we said above, often the size in megapixels indicated in the characteristics of video cameras does not give an accurate idea of the resolution of the resulting image. The manufacturer indicates the number of pixels on the camera matrix (sensor), but not all of them are involved in creating the picture.
Therefore, the parameter “Number (number) of effective pixels” was introduced, which shows exactly how many pixels form the final image. Most often it corresponds to the real resolution of the resulting image, although there are exceptions.
IR (infrared) illumination, IR
Allows shooting at night. The capabilities of the matrix (sensor) of a video surveillance camera are much higher than those of the human eye - for example, the camera can “see” in infrared radiation. This property began to be used for filming at night and in unlit/dimly lit rooms. When a certain minimum illumination is reached, the video camera switches to shooting mode in the infrared range and turns on the infrared illumination (IR).
IR LEDs are built into the camera in such a way that the light from them does not fall into the camera lens, but illuminates its viewing angle.
The image obtained in low light conditions using infrared illumination is always black and white. Color cameras that support night photography also switch to black and white mode.
IR illumination values in video cameras are usually given in meters - that is, how many meters from the camera the illumination allows you to get a clear image. Long range IR illumination is called IR illuminator.
What is Smart IR, Smart IR?
Smart IR illumination (Smart IR) allows you to increase or decrease the power of infrared radiation depending on the distance to the object. This is done to ensure that objects that are close to the camera are not overexposed in the video.
IR filter (ICR), day/night mode
The use of infrared illumination for filming at night has one peculiarity: the matrix of such cameras is produced with increased sensitivity to the infrared range. This creates a problem for shooting in the daytime, since the matrix registers the infrared spectrum during the day, which disrupts the normal color of the resulting image.
Therefore, such cameras operate in two modes - day and night. During the day, the matrix is covered with a mechanical infrared filter (ICR), which cuts off infrared radiation. At night, the filter moves, allowing the rays of the infrared spectrum to freely enter the matrix.
Sometimes switching the day/night mode is implemented in software, but this solution produces lower-quality images.
The ICR filter can also be installed in cameras without infrared illumination - to cut off the infrared spectrum in the daytime and improve video color rendition.
If your camera doesn't have an IGR filter because it wasn't originally designed for night photography, you can't add night shooting functionality to it simply by purchasing a separate IR module. In this case, the color of daytime video will be significantly distorted.
Sensitivity (light sensitivity, minimum illumination)
Unlike cameras, where light sensitivity is expressed by the ISO parameter, the light sensitivity of video surveillance cameras is most often expressed in lux (Lux) and means the minimum illumination in which the camera is able to produce a good quality video image - clear and without noise. The lower the value of this parameter, the higher the sensitivity.
Video surveillance cameras are selected in accordance with the conditions in which they are planned to be used: for example, if the minimum sensitivity of the camera is 1 lux, then it will not be possible to obtain a clear image at night without additional infrared illumination.
| Conditions | Light level |
| Natural light outside on a cloudless sunny day | over 100,000 lux |
| Natural light outside on a sunny day with light clouds | 70,000 lux |
| Natural light outside in cloudy weather | 20,000 lux |
| Shops, supermarkets: | 750-1500 lux |
| Office or store: | 50-500 lux |
| Hotel halls: | 100-200 lux |
| Vehicle parking, warehouses | 75-30 lux |
| Twilight | 4 lux |
| Well-lit highway at night | 10 lux |
| Spectator seats in the theater: | 3-5 lux |
| Hospital at night, deep twilight | 1 suite |
| Full moon | 0.1 - 0.3 lux |
| Moonlight night (quarter moon) | 0.05 lux |
| Clear moonless night | 0.001 lux |
| Cloudy moonless night | 0.0001 lux |
The signal to noise ratio (S/N) determines the quality of the video signal. Noise in video images is caused by poor lighting and appears as colored or black and white snow or grain.
The parameter is measured in decibels. The picture below shows quite good image quality already at 30 dB, but in modern cameras, to obtain high-quality video, S/N should be at least 40 dB.
DNR Noise Reduction (3D-DNR, 2D-DNR)
Naturally, the problem of noise in video did not go unnoticed by manufacturers. At the moment, there are two technologies for reducing noise in the picture and correspondingly improving the image:
- 2-DNR. Older and less advanced technology. Basically, only noise from the near background is removed; in addition, sometimes the image is slightly blurred due to cleaning.
- 3-DNR. The latest technology that works according to a complex algorithm and removes not only near noise, but also snow and grain in the distant background.
Frame rate, fps (stream rate)
The frame rate affects the smoothness of the video image - the higher it is, the better. To achieve a smooth picture, a frequency of at least 16-17 frames per second is required. The PAL and SECAM standards support frame rates at 25 fps, and the NTSC standard supports 30 fps. For professional cameras, frame rates can reach up to 120 fps and higher.
However, it must be taken into account that the higher the frame rate, the more space will be required to store video and the more the transmission channel will be loaded.
Light compensation (HLC, BLC, WDR, DWDR)
Common video surveillance problems are:
- individual bright objects falling into the frame (headlights, lamps, lanterns), which illuminate part of the image, and because of which it is impossible to see important details;
- too bright lighting in the background (sunny street behind the doors of the room or outside the window, etc.), against which nearby objects appear too dark.
To solve them, there are several functions (technologies) used in surveillance cameras.
HLC - bright light compensation. Compare:
BLC - backlight compensation. It is implemented by increasing the exposure of the entire image, as a result of which objects in the foreground become lighter, but the background is too light to see details.
WDR (sometimes also called HDR) - wide dynamic range. Also used for backlight compensation, but more effectively than BLC. When using WDR, all objects in the video have approximately the same brightness and clarity, which allows you to see in detail not only the foreground, but also the background. This is achieved due to the fact that the camera takes pictures with different exposures, and then combines them to obtain a frame with optimal brightness of all objects.
D-WDR - software implementation of wide dynamic range, which is slightly worse than full-fledged WDR.
Protection classes IK (Vandal-proof, anti-vandal) and IP (from moisture and dust)
This parameter is important if you are choosing a camera for outdoor video surveillance or in a room with high humidity, dust, etc.
IP classes- this is protection against the ingress of foreign objects of various diameters, including dust particles, as well as protection from moisture. ClassesIK- this is anti-vandal protection, i.e. from mechanical impact.
The most common protection classes among outdoor CCTV cameras are IP66, IP67 and IK10.
- Protection class IP66: The camera is completely dustproof and protected from strong water jets (or sea waves). Water gets inside in small quantities and does not interfere with the operation of the video camera.
- Protection class IP67: The camera is completely dustproof and can withstand short-term complete immersion under water or long periods of time under snow.
- Anti-vandal protection class IK10: The camera body will withstand a 5 kg load from a 40 cm height (impact energy 20 J).
Hidden areas (Privacy Mask)
Sometimes it becomes necessary to hide from observation and recording some areas that fall within the camera's field of view. Most often this is due to the protection of privacy. Some camera models allow you to adjust the settings of several of these zones, covering a certain part or parts of the image.
For example, in the picture below, the windows of a neighboring house are hidden in the camera image.
Other functions of CCTV cameras (DIS, AGC, AWB, etc.)
OSD menu- the ability to manually adjust many camera parameters: exposure, brightness, focal length (if there is such an option), etc.
- shooting in low light conditions without infrared illumination.
DIS- camera image stabilization function when shooting in vibration or motion conditions
EXIR Technology- infrared illumination technology developed by Hikvision. Thanks to it, greater backlight efficiency is achieved: greater range with less power consumption, dispersion, etc.
AWB- automatic adjustment of the white balance in the image, so that the color rendition is as close as possible to natural, visible to the human eye. Particularly relevant for rooms with artificial lighting and various light sources.
AGC (AGC)- automatic gain control. It is used to ensure that the output video stream from cameras is always stable, regardless of the strength of the input video stream. Most often, amplification of the video signal is required in low light conditions, and a decrease - on the contrary, when the lighting is too strong.
Motion Detector- thanks to this function, the camera can turn on and record only when there is movement on the object being monitored, and also transmit an alarm signal when the detector is triggered. This helps save space for storing video on the DVR, relieves the load on the video stream transmission channel, and organizes notification of personnel about a violation that has occurred.
Camera alarm input- this is the ability to turn on the camera and start recording video when any event occurs: the activation of a connected motion sensor or another sensor connected to it.
Alarm output allows you to trigger a reaction to an alarm event recorded by the camera, for example, turn on the siren, send an alert by mail or SMS, etc.
Didn't find the feature you were looking for?
We tried to collect all the frequently encountered characteristics of video surveillance cameras. If you did not find an explanation of some parameter here that is unclear to you, write in the comments, we will try to add this information to the article.
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Equipment has arrived on the Russian market under a new brand - Expert (South Korea). This release is dedicated to dome cameras (plastic) with a resolution of 680 TVL.
Different manufacturers of video surveillance cameras may name this function differently, so in some variations it is designated by other letter values, for example, Black Mask BLC (BMB) or Eclipse, but the principle of operation remains unchanged.
As you know, video cameras analyze the illumination level of an object and work out these parameters to achieve stabilization by shutter speed or changing the diameter of the aperture on the lens. So, in cases where too bright areas fall into the field of view of the device, the operation of this stabilization mechanism is disrupted and the shutter or aperture adjustment leads to the fact that most of the darkened area around the illuminated one becomes indistinguishable. For example, when shooting a passable area at night, an approaching car with its headlights on falls into the viewing area. Bright car headlights illuminate the picture almost completely, so it is impossible to see the license plate number, the car as a whole, or background details on the monitor.
If in this case we exclude the illuminated areas of the image from the calculation of average illumination, then the remaining details of the image will be better visible and distinguishable. It is precisely this technology that is equipped with the bright light compensation function. In fact, the function simply masks overly lit areas of the frame by overlaying gray areas on them, which leads to a decrease in the overall brightness of the frame and improved visibility of details in dark areas of the image. 
Flaws:
In general, the function is very useful and represents the best solution in many conditions, however, when using the camera in a hall with glass doors that fall into the field of view, it is better to use other functions than HLC, for example BLC, and ideally WDR. The whole point is that using this function the street and objects in the background (that is, behind the glass door) will not be visible, since the background is usually lighter in such places. Thus, the bright light compensation technology will not correctly perceive the brightness of the background and the illumination of the street and will paint most of these areas in gray to eliminate overexposure. In the settings of many surveillance cameras you can find configurations for this function, but in this case they will not bring any special changes, since it will always be lighter outside in the daytime than indoors.
Another inconvenience may befall those who wish to determine vehicle license plates through a video surveillance system using infrared illumination. All license plates are covered with a reflective coating so that at night they are better visible under headlights or other directional lighting. So, this coating reflects light rays in the exact opposite direction, so when IR illumination is applied, infrared rays will be reflected and the number will be bright enough, which in turn will trigger the bright light compensation function. The only solution to this problem is to move the remote IR illuminator to the side to change the angle of refraction of the reflected infrared rays.
Head of the technical support group Benedikt Maksimenko.
