Comparison Dahua DH-SD22204UE-GN-W vs Dahua DH-SD22204T-GN-W

— PTZ (controlled). PTZ is an abbreviation for camera control capabilities - “pan, tilt, zoom”. Accordingly, cameras with this feature are equipped with a movable lens that allows you to aim at the desired object; but the magnification can be either optical (see below) or digital. The advantages of PTZ cameras are obvious: their view is not limited to one position, it can be adjusted at the operator’s request. And some models may provide advanced functions, such as automatic targeting and focusing on movement. On the other hand, similar systems cost accordingly.

- Private mode. A feature that allows you to temporarily pause the camera to protect the privacy of people in its field of view. In private mode, the camera temporarily stops recording video, broadcasting images, and performing other actions related to video surveillance. It is important to note that the implementation of private zones or temporary disabling of recording is available in almost any video surveillance camera. In this case, we are not talking about software capabilities, but about creating conditions in which the camera cannot physically record. So, some models hide the lens inside the body, others turn their “look” away in a predetermined direction (for example, to the corner of a wall). Private mode can be activated forcibly (by pressing a button on the camera body or in a mobile application) or according to a preset schedule.

— PoE power supply. Power technology used in cameras with wired LAN connections. The PoE function allows you to supply power to such a camera through the same cable that is used to transmit the signal - this eliminates the need to run an additional wire to the outlet or use batteries/rechargeable batteries. Of course, to use this technology, the connector of the recorder (or other device) to which the camera is connected must also support it. But it’s worth considering that there are different PoE standards, which primarily differ in power (802.3af power up to 13 W, PoE 802.3at - 25.5 W).

— PoC power supply. An analogue of PoE technology used in traditional cameras: it allows you to supply power through the same cable that is used for the video signal, and thus do without connecting to an outlet and without batteries/batteries. The difference is that PoC operates over a coaxial cable with a BNC connector. Of course, to use this function it must be provided both in the camera itself and in the recorder.

— Panoramic shooting. This feature means that the camera has multiple lenses and covers a horizontal angle of at least 180°, providing a wide field of view when the body is stationary. Such a field of view can be achieved with one fisheye lens (see the corresponding paragraph); however, panoramic shooting has one important advantage: the level of distortion in such video is much lower, even at the edges. On the other hand, the presence of several “eyes” has a corresponding impact on the price and dimensions.

— Setting up a region of interest (ROI). This function allows you to define individual zones in the camera's field of view. Note that the tasks of the selected areas may be different. One option is to configure motion detection zones in the frame, which can reduce the level of false alarms. The second possible implementation is to reduce the quality of less important areas of the image to save storage space. The latter can be especially useful when there is a shortage of data storage capacity, and also if the camera uses communication channels with limited speed or traffic volumes (for example, a 3G/LTE mobile network). Either way, the Region of Interest (ROI) feature reduces camera strain and lets you focus on what's important to you first.

- Light sensor. The presence of a light sensor in the camera design. As a rule, this sensor is used to determine the characteristics of the surrounding environment and automatically adjust to its characteristics - in particular, switching between day and night modes, turning on IR illumination (see below), etc.

— Motion detection. Cameras with this feature are able to detect movement in the field of view. This function is convenient because the vast majority of situations that need to be recorded during video surveillance are associated with movement in the frame. The specific reaction to movement may be different: in some models, recording is turned on, others also send a notification to the recorder or other device, others are able to turn after a moving object, etc. Cameras with this function are especially convenient for monitoring objects where movement is rare - for example, warehouses or underground parking lots at night: for example, turning on motion-based recording only saves storage space and makes it easier to view footage.

— Sound detection. Function for detecting sounds in a protected area. Having “heard” a sufficiently loud sound, a camera with this function can react in one way or another: start recording, sound a warning or alarm, etc. Some models can even play the role of acoustic break sensors, accurately detecting a characteristic impact on the glass and the sound of shrapnel. Support for audio detection automatically means the presence of a microphone (see the corresponding paragraph).

— Microphone. The presence of a microphone in the camera design allows it to record not only the image, but also the sound. This allows you to get a more complete picture of what is happening when recording. In addition, a microphone can be useful if the person in front of the camera wants to communicate something to the operator, and if there is a feedback speaker (see below), even a full dialogue is possible.

— Feedback speaker. The camera has its own built-in speaker. One of the most popular uses of this feature is indicated in the name - it is the operator’s feedback from people near the camera. Thanks to the speaker, you can, for example, voice directly through the camera a hint for a lost visitor, a warning or order for an intruder, etc. In addition, this function can be used for other purposes - in particular, to generate an alarm.

- Mobile app. The ability to work with the camera through an application installed on a gadget such as a smartphone or tablet. As a rule, this control method gives access to both broadcasting/saving video and most settings; but the specifics of the communication between the gadget and the camera may be different. Thus, modern applications often provide for the possibility of remote access via the Internet from anywhere in the world; however, there is another option - a direct communication (usually via Wi-Fi), which only works in the immediate vicinity of the camera. These nuances should be clarified separately. Be that as it may, the mobile application is convenient in that it can be installed on almost any modern smartphone or tablet running Android or iOS, turning the gadget into a portable camera control station.

— Motion alert. A function found in cameras with motion detectors (see above). When motion is detected in the frame, such models are capable of not only taking their own actions (for example, turning on recording), but also sending notifications to the user in one way or another. Specific methods for transmitting alerts may be different - email, SMS, notification on a special web page, etc. But in any case, this function makes it easier to track the observed object and reduces the risk of missing an important event in the frame.

— Alarm input/output. As a rule, cameras with this function are equipped with both inputs and outputs; the number of both may be more than one. These connectors are used to transmit control signals to various components of the security system; they allow you to build a very advanced system and provide additional capabilities for managing its functions. Thus, alarm inputs allow the camera to “react” to commands from other elements - for example, turn on when an electronic lock on the door is triggered. And the outputs, accordingly, are used to transmit commands to external devices - for example, to turn on the spotlight when motion is detected in the frame.

— Audio input/output. The presence of audio input and/or output in the camera design. This feature makes it possible to work with sound, but the features of this work may vary, depending on the specific set of connectors. The audio input itself makes it possible to connect an external microphone, and the audio output allows you to output sound to an external device (for example, a recorder or an amplifier with speakers) via a separate channel. At the same time, these connectors can be used one at a time. For example, a camera with a built-in microphone may only have an audio output, but a model with a LAN or Wi-Fi communication is capable of transmitting an audio signal through the same channel, and for such cameras an audio input is sufficient.

— IR illumination. The presence of an infrared illumination system in the camera design. This illumination is used for operation in night mode: IR illumination is invisible to the naked eye (you can only notice a faint reddish glow of the backlight LEDs, and even then not always), but is well perceived by the matrices of modern surveillance cameras. The ability to do without visible light sources is convenient for a number of reasons: in particular, such work hardly reveals the camera.

— LED backlight. The camera has an LED backlight. Like the infrared illumination described above, this backlight is designed to work in the dark; however, it provides light that is visible to the human eye, allowing the camera to produce a relatively natural-looking color image.

- Card reader. A device for reading removable memory cards, usually standard SD or microSD (specific types of supported cards should be clarified separately). This device performs two main functions. Firstly, it allows you to equip the camera with its own drive - this provides an additional guarantee in case of failures in the external recorder and even allows you to record without any additional equipment at all. Secondly, memory cards allow you to conveniently exchange data with laptops, PCs and other external devices - first of all, transfer footage onto them.

Functions that automate the process of video monitoring, analysis and response to events, which helps to minimize the human factor and increase the efficiency of video surveillance systems.

— Perimeter protection. This option is used when deploying complex video surveillance systems with a recorder and cameras, combining the expanded functionality of intelligent video analytics capabilities for monitoring boundaries. Perimeter protection can cover various functions, for example, tracking the intersection of virtual lines, the appearance or disappearance of objects in the frame, setting up protected zones, if the boundaries of which are violated, an alarm will be activated, and so on. The full list of features should be specified separately. It is important to note that for the listed functions, analysis of objects in the frame can be used - detection of people, classification of vehicles, etc.

— Definition of a person. Cameras with this function can detect the presence of people in the frame by the characteristic outlines of their silhouettes. Once a person's presence is detected, an alarm can be activated, and moving PTZ cameras can follow people in the frame.

— Definition of a car. The ability of a video surveillance camera to automatically recognize and highlight objects in the frame that are vehicles. This can be useful for monitoring t...raffic, controlling parking, or ensuring the safety of roads within a controlled perimeter. A more advanced implementation of this function is license plate recognition (see below).

— Definition of animal. The function of identifying various “living creatures” in the frame: pets, neighbor’s cats and dogs, alien wild animals, etc. Video surveillance systems with this functionality can be used to minimize false alarms, monitor pets to make sure they are safe and in order, and to solve other similar problems.

— License plate recognition. Special tools that provide additional capabilities for reading license plates. The specific capabilities of such tools may be different in different models; they should be clarified separately. So, some cameras only read letters and numbers and transmit the information to the recorder for further processing. Others have built-in databases, so they can compare the read number with the base and provide various actions depending on the result - for example, send a signal to open the barrier if the number is “allowed”. However, in any case, cameras with this feature are well suited for objects where it is necessary to control the movement of cars - for example, parking lots (including closed service ones).

— Facial recognition. Cameras with this function are able to at least recognize the presence of faces in the frame; but the further use of this data and the special functionality of such cameras may be different. Thus, relatively simple models react only to the very fact of detecting a face, but even this provides quite extensive additional capabilities: focusing on a face, tracking a person in the frame (in moving PTZ cameras), etc. And more advanced cameras can recognize characteristic features faces by which a specific person can be identified. This functionality, among other things, allows the surveillance system to compare the faces “seen” by the camera with the stored database and take various actions based on this - for example, allow or deny access, warn about an unwanted visitor or unauthorized use of a key card, etc. P.
Note that face recognition tools can also be found in recorders to which cameras are connected. However, the presence of such functions in the cameras themselves can also be useful - especially if the existing recorder “does not shine with capabilities” in this regard, or the system does not have a recorder at all (for example, it consists of IP cameras connected via a router to a PC).

— People counting. A function that allows the camera to count the number of people in the frame; the received data is stored in its own memory and can be sent to a recorder or other external device. Note that in most models this feature is combined with the face recognition described above, thanks to which the camera is able not only to count all people in a row, but to recognize tech who are in the frame again. However, people counting can be used for both statistical and security purposes. For example, at large facilities such as office and shopping centers, it allows you to determine whether all visitors who entered the premises left it before the end of working hours.

The size of the matrix installed in the surveillance camera (diagonally).

In general, larger sensors (with the same resolution and sensor type) are considered more advanced: they get more light, which has a positive effect on image quality (especially in low light). On the other hand, increasing the size affects the cost of the entire device; and in some cases (for example, if the camera is not planned to be used in twilight and darkness), a relatively small sensor may be quite suitable.

As for specific dimensions, the most modest cameras in terms of this indicator have matrices of 1/4 "or less. Models with sensors of 1/3.8" - 1/3" and 1/2.9" - 1/2" are very popular, these values can be called average. And in advanced devices, diagonals and more than 1/2 "(up to 1/1.7") are found.

The lowest degree of illumination of the scene being shot, in which the camera is able to provide normal visibility. Usually, this item specifies the values for the daytime mode of operation (in the night mode, the minimum illumination in many models may be zero at all, because in such cases the IR illumination is turned on, see "Design and capabilities"). And if the camera is capable of shooting in colour, it usually means the lowest illumination necessary to obtain a colour image.

The lower this indicator, the better the camera works in low light, the brighter and more clearly visible image it is able to provide in such conditions. At the same time, note that in low light, night mode is often preferable, and in the presence of the aforementioned IR illumination, it is more likely to focus on the range of its operation (see above).

There are comparative tables that allow you to evaluate the degree of illumination indicated in the characteristics from a practical point of view: for example, an indicator of 0.2 lux corresponds to clear eyes on a full moon.

The signal-to-noise ratio that the surveillance camera corresponds to.

This indicator describes the ratio of the level of the useful signal (the actual image produced by the camera to an external device) to the level of extraneous noise that inevitably arises during the operation of electronic circuits. Such noise appears in the image as characteristic noise (“snow”). The higher the signal-to-noise ratio, the less interference on the screen, the clearer and better the image is, and the smaller the volume of recorded video files. It is believed that visible noise practically disappears at a ratio of at least 45 dB. However, among modern cameras there are also higher rates.

Horizontal viewing angle of the surveillance camera. For models with a variable value, the maximum value is indicated, since it is the width of the image that is important, and when zooming in, the zoom factor is more important than the angle. This paragraph also indicates the general angle of view for models with a circular field of view – in particular, cameras with a fisheye lens (see above)

The wider the viewing angle, the more space the camera captures and at the same time, the smaller the images of individual objects in the frame are obtained. Therefore, when choosing by this parameter, it is worth deciding what is more important – the ability to view a large scene or the visibility of small details in a relatively narrow field of view. Also note that with a wide field of view (100° or more), characteristic distortions can be observed at the edges of the frame, and the wider the angle, the more pronounced they are. This phenomenon can be eliminated by panoramic shooting (see "Design and features"), but this feature, in turn, complicates and increases the cost of the camera.

The video compression format used by the camera.

Compression is used to reduce the file sizes of captured video; different technologies can be used for this — the so-called codecs, their list is given in this paragraph. From a practical point of view, compatibility with external recording and playback devices primarily depends on the supported codecs. If you plan to use a computer as a recorder / player, you can ignore this list: modern PCs and laptops usually support a very extensive list of formats, and in extreme cases, the missing codecs can be installed separately. But if we are talking about specialized registrars, individual players (like home media centers), etc. — codec compatibility should be clarified further. So, if the advanced modern H.265 standard is very widely supported nowadays, then the more specific H.265+, originally created for surveillance systems, is much less common even in specialized equipment.

The highest relative humidity at which the camera is able to operate normally, without failures and breakdowns, for an unlimited time.

Modern electronics tolerate low humidity well, but high rates affect it negatively — with a long stay in such an atmosphere, moisture can condense on certain parts of the structure and various unpleasant consequences, from corrosion to short circuits and fires. Therefore, you can use the camera effectively and safely only in conditions where the humidity does not exceed the maximum recommended value specified in the specifications. At the same time, we note that many devices are able to endure short-term (up to several hours) exposure to high humidity without consequences.

The main material used in the construction of the camera body.

— Plastic. Inexpensive and at the same time quite practical material. Plastic is light, quite strong (not as strong as metal, but still quite sufficient for most cases), chemically inert (and therefore not susceptible to corrosion and insensitive to moisture), and also has a relatively low thermal conductivity (which provides additional protection for extreme temperature fluctuations). Due to all this, this material is very popular in indoor chambers (see "Usage"). At the same time, it is somewhat less suitable for outdoor work.

— Metal. The main advantage of metal, in comparison with plastic, in the case of surveillance cameras is high strength and reliability. This allows you to use it even for street models that work in difficult conditions and must have a certain anti-vandal resistance (at least not immediately “give up” when trying to break or break). At the same time, such material is much more expensive, and therefore less common.