Megapixel cameras in security television: pros and cons.
I'll be brief: megapixel video cameras have only one advantage — a large number of pixels. All other things being equal (which, of course, does not happen), this is good. Everything else is disadvantages. Let's take a closer look.
The first obvious drawback is the price. Please note that we are not only talking about the price of the video camera itself, to realize its capabilities you will also need a very expensive lens, as well as the entire infrastructure (network, storage devices, monitors) that can digest the gigabytes of data produced by a megapixel video camera.
A regular video camera has about half a megapixel. A 2-megapixel video camera should at first glance replace four regular ones (it has four times as many pixels), and this fact is often played up by managers advertising megapixel equipment. However, in most cases, only a narrow strip is important in the camera's field of view, so it is not the total number of pixels that matters, but their number by width or height, so one 2-megapixel camera will only replace two regular half-megapixel ones.
This can be easily understood with examples. If your object is located in the middle of a field and you need to examine all approaches, then you will need either 8 (regular) cameras with a 45-degree field of view, or (to provide the same angular resolution) 4 two-megapixel cameras with a 90-degree field of view. The latter will also have a significantly larger vertical field of view, so in addition to covering the horizon, they will provide the ability to observe birds in the sky and ants on the ground. This can be useful, although you are unlikely to be willing to pay extra money for such an opportunity. As a result, you can use only half as many cameras, although each contains four times as many pixels.
Another example: video cameras are installed along a fence, one after the other. A regular video camera with sufficient resolution can monitor an area 15 meters wide and 70 meters long. A two-megapixel camera can distinguish twice as small details, and therefore can monitor 140 meters in length. At the same time, the monitored strip will be wider — 30 meters — so that the frame will include bushes inside the object and the road outside the fence. This is generally good, but not required, however, only half as many megapixel video cameras will be needed, although each contains four times as many pixels. Finally, the third example. A video camera with a 90-degree lens is installed in the corner of a 5 by 5 meter room. The entire room is covered, in the far corner a resolution of 100 pixels per person's height is provided. This is probably not enough to recognize even a familiar person (it is generally accepted that 200-250 pixels per height are needed, and this amount is only in the center of the room and two other corners), but it is more than enough to determine what a person is doing. Moreover, if the door to the room is not in the far corner, then the person will certainly be at least twice at a distance at which he will be easy to recognize. If we install a megapixel camera, we will still have to install one camera (we can’t install a quarter of a camera), although the image quality will improve — there will be 200 pixels per person’s height even in the far corner, which will ensure guaranteed recognition of a well-known person anywhere in the room, all the time while he is walking there, but still, most likely, this will not be enough to recognize a stranger, for example, from a video recording. In this example, we see that the quality has improved somewhat, although the number of video cameras has remained unchanged, at least half a megapixel, at least two, at least ten — you still need to install one camera per room.
The second drawback, well known to professionals, but carefully hushed up by sellers, is sensitivity. Roughly speaking, sensitivity depends mainly on the size of an individual cell. If a half-inch matrix contains two million pixels, its sensitivity is approximately equivalent to a regular (half-megapixel) quarter-inch matrix, and almost half as good as standard third-inch video cameras. If you remember that almost all megapixel cameras are color, and color ones, firstly, have a cell size that is half as big (half of the pixel is green, and half is red or blue), and secondly, they also have filters that let through only the desired color, and therefore their sensitivity is 10 times less than a standard-resolution camera of the same size. Of course, in real life, high sensitivity is not that important. It only means that you can install fewer lighting lamps. Good half-inch black-and-white regular (half-megapixel) cameras can be sensitive enough to do without additional lighting in urban conditions. Color cameras, especially megapixel ones, will always require sufficiently high illumination. By the way, the popular cameras with the «day/night» mode are actually color cameras. Even those that really expand the spectral range of sensitivity in the «night» mode (for example, they have additional «fourth» color cells or a mechanically retractable filter), nevertheless, have a sensitivity three to four times lower than that of real monochrome cameras. Most cameras with the declared «day/night» mode actually simply turn off the color signal at night, which does not increase sensitivity at all, but only eliminates visually unpleasant color noise.
However, sensitivity is not only important in itself. Much more important is that matrices with large sensitive cells provide a better signal-to-noise ratio under normal illumination. In addition, large cells can accommodate more electrons, which allows for smooth transmission of many gradations of brightness. Matrices with poor sensitivity, in addition to poor sensitivity itself, always have a poor ability to transmit halftones. And since in real life (not in the movies) interesting objects have low contrast (for example, a criminal in camouflage against the background of bushes), poor ability to transmit halftones will lead to a complete loss of distinguishability of the object. By the way, pay attention: in mass-produced simple cameras with a small (10 mm) matrix, the number of megapixels has recently been at least 14, or even 16. While much (10 times) more expensive semi-professional cameras with a 20 mm matrix usually have even fewer megapixels — only 12 or 14. Naive buyers of cheap point-and-shoot cameras believe that many megapixels mean a lot of quality. More advanced users know that megapixels are just one facet of quality, and it should not be overestimated at the expense of other parameters that are not so obvious. Of course, the most expensive professional cameras have a huge matrix — 40 mm and at least 30 megapixels, and all parameters are at a level. True, the price is also 10 times higher. So, happiness is not only in megapixels if you want to get high quality.
And finally, I will mention a very minor drawback of megapixel cameras. As a rule, the more megapixels in each frame, the fewer frames per second the camera processor can process and the network cable can pass. For megapixel cameras, 10 frames per second is considered quite acceptable, like in Chaplin films. For security purposes, in most cases, this is quite enough. Unless, of course, we are talking about monitoring cars on a busy highway. A car moving at a speed of 40 meters per second (140 km/h) in 1/10 of a second moves exactly its length, so it may not get into the previous frame, or the next one at all. In general, this drawback is really not very important. But, as in the case of sensitivity, there are other manifestations of this drawback, not so obvious, but more dangerous. If the processor has difficulty processing several megapixels, the manufacturer is tempted to turn on a simplified mode in digital compression. This means that if the processor does not have time to find all the small details in the frame, it will not transmit them. The number of frames (an easily observable quality parameter) will thus reach 50 per second, but as a result, the image resolution after compression will be significantly reduced. This is difficult to notice with the naked eye, as there are virtually no standard methods for measuring the quality of compression algorithms, no objective parameters that could be easily checked. This will be especially evident with sharp movement in the frame, when the processor will be overloaded with large changes in the frame relative to the previous one. It is very likely that a still image will provide all the declared megapixels, but when a criminal appears in the frame, the system will shamefully lose all quality and display a blurred figure. Perhaps the processor supports a mode in which the number of bits per second transmitted to the network will increase in this case. This is better, but it means that when designing a network, you will have to include a multiple reserve in the performance of switches, so that in the event of active large movement in the field of view of several video cameras, the entire network does not suddenly stop, and it does not turn out that the picture has completely disappeared.
In general, let my previous words not deceive you, the transition to megapixel cameras is undoubtedly a big step forward in security technology. It is no coincidence that these cameras have already firmly occupied their niche in the market, and the demand for them is constantly growing. That is why we present to the attention of readers several models of megapixel cameras from leading manufacturers.
AXIS Q6034/-E (AXIS)
Designed for the most demanding applications, the outdoor PTZ dome camera provides large area coverage with HDTV-quality video, excellent zoom detail and fast pan/tilt control.
Delivers high image quality. HDTV 720p complies with the SMPTE 296M standard with a resolution of 1280 x 720 pixels, full frame rate, high HDTV color accuracy and 16:9 aspect ratio support. Supports simultaneous transmission of multiple video streams in H.264 and Motion JPEG formats.
The IP66 and NEMA 4X rated AXIS Q6034-E does not require an external housing. Arctic Temperature Control ensures that the camera remains on even at -40°C.
SNP-5200H High-Speed PTZ IP Camera (Samsung)
1/3” 1.3 MP progressive scan Mega CMOS sensor. Built-in HD lens with 20x (4.45~89mm) optical zoom. 360° rotation, speed up to 500°/sec. IP66 housing, fan/heater (-50°С to +50°С). Maximum resolution 1280×1024 (SXGA). 16:9 HD mode (1280x720P). Encoding speed up to 30 fps at any resolution. Multi-stream encoding in H.264, MPEG4 and MJPEG formats. Day/night mode (with IR filter). Minimum illumination 0.08 lux (F1.6, 50IRE, b/w). SSDR dynamic range expansion technology.
2D+3D SSNRIII noise reduction technology. Intelligent video analysis. Supports bidirectional audio. SD card slot for local recording. hPoE (Power over Ethernet). Analog output (BNC). Complies with the ONVIF standard.
Panasonic
Panasonic WV-SW395 and WV-SW385 network PTZ cameras are a continuation of the i-PRO camera line, SmartHD series. They use a highly sensitive dual-speed 1.3 MP progressive scan MOS sensor. The image of 1280×960 pixels is transmitted at a speed of up to 30 fps. Coding in H.264 and JPEG formats allows simultaneous viewing in real time and recording with the best quality. It is worth noting the 18-optical (f = 4.7 ~ 84.6 mm) zoom, Super Dynamic and ABS functions for increasing the dynamic range, digital noise reduction (DNR), motion detector (VMD), face recognition function, Russian-language interface, the presence of a slot for SD/SDHC cards and PoE support (PoE + for WV-SW395). The cameras comply with the ONVIF standard.
Hikvision
The Hikvision DS-2DF1-572 outdoor network HD PTZ camera has a 1.3” SONY CCD progressive scan, resolution — 1.3 MP. H.264 video compression, transmission rate — 25 fps (1280-720) or 12.5 fps (1280-960); support for DualStream technology, two-way audio transmission (OggVorbis audio codec). 18-fold optical (f = 4.7 ~ 84.6 mm) and 12-fold digital zoom. The camera supports TCP/IP, HTTP, DHCP, DNS, RTP/RTCP, PPPoE, FTP, SMTP, NTP and SNMP protocols. Up to 6 users simultaneously. Control is possible via web interface, free software iVMS-4000, as well as from hybrid and network (NVR) Hikvision recorders. It is possible to record to SD/SDHC card.
HD PTZ camera Sony SNC-RH164
It is based on a 1/3” CMOS sensor and provides an image resolution of up to 1280 x 720 with a flow of 30 fps. The electronic part of the camera supports work with three codecs H.264/MPEG-4/JPEG and Dual Stream mode in any combination of codecs.
The SNC-RH164 is a day/night camera. The Visibility Enhancer function and XDNR, a dynamic noise reduction system, will help significantly improve the quality of HD images in difficult lighting conditions.
The presence of a Compact Flash card slot allows for backup recording in the event of a network connection failure. The optical block of the cameras provides 10x optical zoom, while the range of horizontal viewing angle change is from 50o to 5.4o.
The SNC-RH164 model is designed for outdoor installation. The camera housing provides protection in accordance with the IP66 standard. The operating temperature range of the SNC-RH164: from -40 ° C to + 50 ° C.
Spectra HD High-Speed PTZ Dome IP Camera (Pelco by Schneider Electric)
The Spectra HD IP camera combines the features of the Spectra high-speed PTZ dome with high-tech Sarix megapixel technology.
Spectra technology provides a wide range of performance options, including an outdoor version (with a minimum temperature of -51° C), excellent PTZ characteristics, including variable rotation speed, continuous 360° rotation, presets, tours and privacy zones, and Sarix brought advanced network technologies and high quality video images with high resolution and realistic color rendition. Spectra HD is built on a matrix with a resolution of 1.3 megapixels, has a built-in 18x optical zoom and an additional 10x digital zoom.
Spectra HD has a day-night mode, extended dynamic range, autofocus, autotracking and motion detection, a built-in USB slot for connecting audio accessories or an alarm module.
The camera supports multicast mode and produces 2 independent video streams with H.264 or MJPEG compression. Power is supplied via PoE (IEEE802.3af) or using 24 VAC power supplies.