Comparison Dahua DH-SD49225I-HC vs Hikvision DS-2DE4220IW-D

-LAN. The LAN (Ethernet) interface was originally intended for building wired computer networks. Cameras with this connector, usually, also work as network devices. The advantage of this option over the Wi-Fi described below can be called a higher actual bandwidth, over BNC — the ability to connect without additional equipment, directly to a standard network router used for a regular computer network. Of the shortcomings, one can only note the need to pull the wire, but this point is common to all wired connection options. For the rest of the features, LAN is the most convenient, thanks to which it has become widely used in modern security cameras.

— Wi-Fi. The Wi-Fi connection was originally a wireless analogue of the LAN described above and was used to connect to computer networks. When working in such networks, this connection is similar to LAN in the sense that it allows the camera to work through a regular router (of course, supporting Wi-Fi). At the same time, Wi-Fi is more convenient due to the lack of wires, however, with an abundance of other wireless devices connected to the router, the channel bandwidth and image quality can noticeably deteriorate. Note that recently it is also possible to use this connection in the Direct mode — for direct connection of the camera with another device, for example, connecting the camera to a smartphone (see "Design and...capabilities — P2P"). However, this option is less common.

— BNC. Abbreviation for Bayonet Neill Concelman. A bayonet type connector commonly used for analogue video signal transmission. Refers to professional video interfaces, special equipment is required to work with such a camera. However, by themselves cameras with connectors of this type, usually, belong to the lower price range. This is due to limited connectivity via BNC — only a video signal can be transmitted through it, which limits the functionality of such cameras compared to models that work via LAN or Wi-Fi (see above).

— 3G / 4G. Internet connection via 3G / 4G mobile networks; usually, for this you need to install a SIM card from a mobile operator in the camera. The speed of such networks allows, among other things, to broadcast video in a fairly high resolution. So such a connection (of course, with coverage) is well suited not only as a fallback in case of interruptions to the Internet, but also as the main communication channel if there is no fixed Internet connection at all. A typical example of the second situation is the observation of a country house located "far from civilization", but in the zone of reliable mobile communication reception. Moreover, in both cases, you can contact the camera via the Internet from anywhere in the world.

— 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.

The number of backlight LEDs (see "Design and capabilities") provided in the camera design.

Theoretically, more LEDs provide more power and, accordingly, range (see below) and efficiency of IR illumination or LED illumination. However, in fact, such light sources can vary markedly in performance; in addition, a lot also depends on the features of the camera itself. Therefore, in fact, this indicator is a reference, and when choosing, it makes sense to pay attention to parameters that are closer to practice — in particular, the same backlight range (see below).

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.

— WDR (Wide Dynamic Range) — extended dynamic range. WDR technology combines several frames with different exposures into one picture, as a result, dark areas are brightened, and overexposures are darkened, and the output is a picture with extremely uniform lighting. The true wide dynamic range technology is called True-WDR and it is implemented in the optical circuit at the hardware level, a special microprocessor is responsible for creating and mixing exposures. A more affordable alternative to wide dynamic range is Digital-WDR technology, which equalizes lighting through software algorithms.

— DWDR (Digital Wide Dynamic Range) — extended dynamic range technology based on software brightening algorithms. DWDR brightens too dark areas of the frame, which can be completely blurred against the background of light areas. Digital brightening allows you to noticeably improve the quality of shooting in contrasting lighting conditions. Digital WDR cameras are noticeably cheaper than true True-WDR optics. Of course, the quality of digital brightening is inferior to True-WDR.

— BLC (Back Light Compensation) — backlight compensation technology. This system is based on the work of digital signal processors DSP. So, the device, relatively speaking, "breaks" the frame into many segments, making its own adjustments to each of them. Backlight compensation brightens dark areas of...the frame well. The main disadvantage of the technology is the increase in the brightness of the already bright areas of the frame, due to which overexposure may appear in the picture.

— WDR+BLC. The camcorder supports several lightening technologies at once, each of which is described in more detail above. Immediately, we note that the combination of WDR + BLC allows you to achieve an extremely clear and clear picture in almost any lighting conditions, from extreme contrast to insufficient and excessively bright.

— DWDR+BLC. The device supports two popular clarification technologies at once, each of which is described in more detail above. The presence of DWDR + BLC technologies allows the camera to effectively brighten the dark areas of the frame. Such video cameras have proven themselves well when working in low light conditions.

Focal length of the camera lens.

The focal length is such a distance from the lens to the matrix, at which a clear image is obtained on the matrix (when the lens is focused to infinity). The viewing angles of the lens primarily depend on this indicator (see below): the smaller it is, the wider the viewing angles and the smaller the objects in the frame (and vice versa). At the same time, it should be noted that the actual viewing angle is determined not only by the focal length, but also by the size of the matrix (see above). In fact, this means that with different sizes of matrices, lenses with the same focal length will have different working angles. Therefore, only cameras with the same matrix size can be compared with each other according to this indicator. Among CCTV cameras, lenses with a focal length of 2.8 mm, 3.6 mm, 4 mm and 6 mm are considered popular.

In models with a variable focal length (see above), in this case, the range from the minimum to the maximum distance is indicated. Also, using these data, you can derive the optical magnification factor of such a lens: for this, the maximum value must be divided by the maximum (for more details, see below).

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.

Modern surveillance cameras can provide two types of magnification - optical and electronic. In the first case, the “approximation” of the image is carried out due to the operation of the lens; in the second, a separate area is selected on the matrix and the image from it is “stretched” across the entire frame, creating a magnification effect. Thus, optical zoom is more advanced: it allows you to use the entire sensor area even when zooming in.

Optical zoom is only available if the camera lens has a variable focal length (see “Focal”). And the degree of magnification will correspond to the ratio between the maximum and minimum focal length: for example, for a model with a range of 3 – 15 mm it will be 15/3 = 5x. Thus, we are not talking about how much the camera enlarges the “picture” relative to how it is visible to the naked eye, but about how much larger the image is at the maximum focal length than at the minimum.

The disadvantages of optical zoom systems are directly related to the disadvantages of variable focal length: the lenses are larger, more expensive and less reliable than with electronic ones. In addition, the capabilities of this operating format are limited: too high magnifications would require too bulky and expensive optical systems. Therefore, manufacturers often use a compromise option, supplementing optical magnification with electronic one: the first option is used at low magnifications, the secon...d is turned on when the capabilities of the optics are exhausted.