We all know how to choose a camera, but not everyone can do it correctly. While the network is flooded with reviews of any technique, the disappearing little becomes materials in which the capabilities of the devices are truly disclosed.
Optical devices suffered the most in this respect. Everyone knows about megapixels and resolution, but when it comes to more subtle matter, begins to "swim". If you are thinking about buying a camera (and are not an expert in this field), it will be useful to understand what the abstruse terms in characteristics actually mean. To understand is not only to read the description.
About the obvious
If you start Google "by what characteristics do you choose a CCTV camera" , Will be able to get acquainted with the amazing world of the Internet zero. Where black-and-white cameras still live, analog cameras, the importance of photosensitivity in luxes. Some characteristics overlap (and mutually annihilate) – do not forget about it.
So we'll focus on modern IP cameras that support Ivideon's cloud service, and we will not touch upon the obvious characteristics. Most likely, you understand the difference between the resolution of 1080p and 720p, diagonal and horizontal viewing angles, and also know about infrared LED lighting.
However, often in the description of cameras you can find abbreviations: 3DNR, AWB, AGC, WDR and others. What is it and why can not focus only on megapixels, resolution and viewing angle? Is it important to understand all the characteristics at all, or is it enough to see an example of the video recording of the selected camera once?
WDR (Wide Dynamic Range)
WDR (Wide Dynamic Range) – Wide dynamic range. This technology allows you to get high quality images at any difference in light levels.
Dynamic range is a camera parameter that characterizes its ability to transmit in the image of each frame very bright and very dark elements of the scene. The dynamic range is denoted in decibels (dB).
The dynamic range (DD) of a real part of the territory usually significantly exceeds its own camera DD, which in most cases is at the level of 52-60 dB: a cloudless sunny day on the street is 180 dB, and a well-lit room – from 126 dB to 140 dB.
One way to eliminate this drawback is to use a mathematical algorithm for processing each image frame, as a result of which it is possible to redistribute the brightness in such a way that s frame of information has become saturated. This technology is called the Wide Dynamic Range, although in fact it does not have anything in common with the dynamic range.
A camera without WDR is not able to give a clear image of objects in the shadow where there are both very bright and shaded Areas or light falls from behind, for example, if a person stands on a background of a brightly lit window.
Typical situations when it is difficult to do without WDR:
- watching the front door when the sun is shining outside, and inside is a dark room – a common case in shops and office buildings;
- surveillance of cars entering the garage or tunnel;
- in transport, while observing the perimeter of buildings and in other cases when part of the frame is under direct sunlight, and other parts are hidden in deep shadows;
- when driving directly to the camera of cars with bright headlights;
- where there is a large amount of reflected light, for example, in office buildings or in shopping malls.
The WDR is calculated as the ratio of the luminosity of the brightest and the faintest object that was captured by the matrix. For each frame, the matrix makes several scans with different shutter speeds of the electronic shutter and produces preliminary images-one with a long exposure for clarifying all the dark parts of the frame, the other with a short exposure with a more correct display of the re-illuminated areas. After that, fragments with better contrast transfer are added to the resulting frame, balanced in brightness.
BLC (Back Light Compensation)
Back Light Compensation – compensation of backlight. The technology allows you to compensate brightly illuminated background for a good study of objects located in the foreground. Because of the BLC, information is lost in the brightly lit parts of the scene, but the objects in the foreground become well-developed.
With BLC, the microprocessor aligns (smoothes) the illumination across the entire field of view of the camera. Most cameras today have support for BLC, but it does not compare to the capabilities of the Wide Dynamic Range. At best, BLC helps balance lighting conditions to find out what's in the foreground of the image, but the background remains blurry.
3DNR (3-Dimensional Noise Reduction)
3-Dimensional Noise Reduction (3DNR) – three-dimensional noise reduction. 3DNR technology suppresses noises in the image, which appear in low light conditions when there are fast moving objects in the frame. 3DNR analyzes the differences between consecutive frames of the video image and suppresses noise by mixing data on the frame.
The disadvantages of the algorithm include additional defects and blurring, which appear when moving in a frame. However, if the noise reduction mode is enabled only for individual frames, then the resulting image is obtained both not noisy, and qualitative.
AWB (Auto White Balance)
AWB – automatic white balance. The function compensates for color distortions caused by different lighting sources (sunlight, incandescent lamp or fluorescent light), cutting off an unnecessary spectrum of light. In this case, the camera sets the color temperature of the image so that the resulting colors in the image have the same shades and look exactly as they are perceived by the naked eye.
There are several different AWB algorithms, but most of them are divided into two categories. Global algorithms use all pixels of the image to estimate the color temperature. Local algorithms use only a subset of pixels based on predefined selection rules for this task. There are also hybrid algorithms that choose the best algorithm based on the image content.
AGC (Automatic Gain Control)
AGC – automatic gain control.
The AGC begins to work when the illumination at the object is low and the fully open aperture is unable to compensate for the lack of illumination. The camera will automatically amplify the video signal received in lower light conditions to optimize the sharpness of the image in a poorly lit scene. However, the more the signal amplifies, the higher the level of interference on the screen.
ROI (Region Of Interest)
Region Of Interest – area of interest . The technology allows you to set the enhanced image quality in the selected areas selected on the screen. The area selected on the frame is recorded with the maximum quality, the rest of the image is recorded with a lower resolution. The use of this function significantly reduces the traffic and the space occupied by the archive.
IR illuminates the face, making it difficult to identify when the person is close To the camera. Smart IR is a technology that allows you to adjust the intensity of the camera's IR LEDs to compensate for the distance to the subject. When shooting in the dark, the adaptive IR illumination Smart IR automatically adjusts the radiation power depending on the distance to the observed object in the frame, allowing you to get an image without overexposed areas.
The implementation of technology HLC in Hikvision cameras
High light compensation – compensation of bright light. In automatic mode, the bright spot is monitored and a repeated shot is done, ignoring the data from the matrix cells in this place. HLC is used to eliminate the negative effect on the camera's work of a bright light source falling into the lens. Most often this mode is used in the fight against the light of automobile headlights. In addition, HLC helps to eliminate even a small, but noticeable exposure to street lamps.
The video above shows the recordings from two CCTV cameras (Hikvision and Nobelic), in which the technical specifications are almost identical. As you can see, the recording of the camera is conducted in different ways. It is impossible to say unequivocally that some video stream turned out to be worse than the other. Nevertheless, the difference is visible to the naked eye. On which decision to stop your choice – depends only on your needs, personal opinions and relationships on other parameters (for example, at a price).
Which image is better?
We listed not all the additional capabilities of the cameras, but we sorted out the moments that cause the most Questions from our users. There are you want to improve your knowledge in theory, there are many different sources – for example, A. Gont's book "Practical Guide to Video Surveillance." However, theory alone is not enough to choose a CCTV camera. Always see examples of the video!