There are several basic problems with HD network cameras?
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What is HD monitoring?
For video surveillance, image clarity is undoubtedly the most critical feature. The clearer the image, the more obvious the details, the better the viewing experience, and the higher the accuracy of application services such as intelligence. So image clarity is the eternal pursuit of video surveillance.
The standard for measuring image sharpness is resolution, and the unit is pixel. The larger this value, the clearer the image. The so-called HD, SD, the difference is also reflected here. The dividing line between the two is megapixels or 720p, reaching megapixels or 720p is HD. Based on such standards, CIF and D1, which currently dominate the video surveillance market, are standard definition.
Whether it is from the perspective of resolution, display effect or fluency, HD has more advantages than SD. In terms of resolution, the resolution of 720p is 9 times that of CIF, the resolution of 1080i/1080p is 20 times that of CIF, and in the same display environment, HD will be much clearer. From the display effect, HD supports both large-screen display and 16:9 wide-screen display, which can greatly enhance the user's viewing experience. In terms of fluency, HD supports higher frame rates. For example, 720p and 1080i/1080p can both support 60 frames per second or 60 fields per second, and its image fluency is twice as high as standard definition. Therefore, high-definition monitoring will inevitably replace standard definition monitoring.
Why HD front end monitor must be HD network camera?
We know that traditional SD monitoring is divided into analog, digital, and network types. The front end of the analog monitor is an analog camera, and the back end is a matrix. The digital surveillance front end is also an analog camera and the back end is a DVR. There are two types of network monitoring front-ends, one is an analog camera + video encoder, one is a network camera, and the back end is a platform. In other words, in the era of SD surveillance, there are many types of analog cameras, network cameras, video encoders, and analog cameras at the front end.
Then why did the high-definition monitoring era, the front end must be high-definition network camera? There are two main reasons.
First, high-definition monitoring must be networked. It must be based on video compression processing and transmitted over an IP network. This is the only way to control the transmission cost of high-definition video.
Uncompressed high-definition video signals after the acquisition have both analog and digital transmission methods. Analog transmission generally uses YPbPr component transmission, and one HD video signal needs three coaxial cables to transmit at the same time. Digital transmission generally uses DVI, HDMI, or HD-SDI transmission. The transmission distance of DVI or HDMI is only a few meters, which is not suitable for monitoring and transmission. Although HD-SDI can transmit about 100 meters, it has high requirements for coaxial cables. Cable prices are also very expensive. Whether it is analog or digital transmission, the transmission cost of uncompressed high-definition video signals is significantly higher than that of analog SD video signals. With video compression coding and transmission over IP networks, the difference in transmission costs between high-definition video and standard-definition video is small.
Second, the efficiency and cost of directly using high-definition network cameras for front-end processing are better than using high-definition video encoders and high-definition cameras.
The current high-definition video sensor is mainly CMOS. The CMOS sensor directly outputs the digital video signal. In the camera, the digital high-definition video signal is directly compressed and encoded by the DSP or ASIC, and then transmitted in a networked manner, and the HD signal is output directly from the camera. It is economical and more efficient.
This is why all high-definition surveillance front-ends we can see on the market today are HD network cameras.
Which of CCD and CMOS is more suitable for HD network cameras?
There are three core components of a webcam: a lens, an image sensor, and a compression processing chip. Among them, the image sensor is the core of the image acquisition and processing part.
There are two types of image sensors: CMOS and CCD. The difference between the two has been discussed very much, mainly reflected in the sensitivity, cost, noise, power consumption and other aspects: 1) In the same pixel size, the CMOS sensor's sensitivity is lower than the CCD sensor 2) The cost of the CCD sensor is higher than that of the CMOS sensor; 3) The resolution of the CCD sensor of the same size is generally better than that of the CMOS sensor; 4) The noise of the CMOS sensor is larger than that of the CCD sensor; 5) The CCD sensor is not only in the power management In addition to the higher difficulty in circuit design, the high driving voltage makes its power consumption much higher than that of CMOS sensors.
In the era of SD surveillance, whether it is an analog camera or a standard definition network camera, the most widely used is a CCD. In the era of high-definition surveillance, the situation will change. High-definition monitoring is very sensitive to the cost. Although the image quality of the CMOS sensor is not as good as that of the CCD, its cost advantage poses a great threat to the CCD. Of course, the outcome of the game between the two will ultimately be determined by the price/performance ratio. Whoever can guarantee that the better image quality is not expensive will win.
Judging from current trends, the chance of CMOS winning is significantly greater. On the one hand, with the development of technology, the sensitivity of CMOS is rapidly improving. It is reported that manufacturers currently dedicated to CMOS research in the market have developed 720p and 1080p dedicated CMOS devices whose sensitivity performance is close to that of CCDs. On the other hand, although the resolution of CCD sensors of the same size is better than that of CMOS sensors, the advantages of CMOS in terms of throughput can effectively overcome the difficulties in manufacturing large-sized photosensitive originals without considering the size constraints, so that CMOS is at a higher resolution. Will have more advantages. In addition, the CMOS response speed is faster than the CCD, so it is more suitable for the large data volume characteristics of high-definition monitoring.
Therefore, although CCD and CMOS have their own advantages in different application scenarios, with the continuous improvement of CMOS processes and technologies, and the continuous decline in the prices of high-end CMOS, future high-definition network cameras will have more choices for CMOS.
Page 2: What is the difference between HDTV and megapixel?
As we mentioned earlier, the standard for measuring image sharpness is resolution. In so-called high definition, resolution must reach megapixels or 720p. So what's the difference between megapixels and 720p?
720p is derived from the HDTV standard developed by the Society of Motion Picture and Television Engineers (SMPTE). According to this standard, there are mainly the following three formats that truly meet HD video:
L720p: 1280*720 resolution, 16:9 widescreen display, progressive scan / 60Hz
L1080i:1920*1080 resolution, 16:9 widescreen display, interlaced/60Hz
L1080p:1920*1080 resolution, 16:9 widescreen display, progressive scan/60Hz
In addition, the standard also defines the frame rate and other data corresponding to each resolution in detail. Therefore, an HD network camera that satisfies any given HDTV standard necessarily supports one or more specific resolutions, frame rates, and color fidelity, so that the specified video quality is always guaranteed.
While megapixels is not a recognized standard, it merely represents the concept of an industry best practice and specifically refers to the number of image sensor elements of a network camera. In other words, when we hear a HD network camera that supports megapixels, 2 megapixels, or 5 megapixels, we don't know what the frame rate of this camera is, how the video aspect ratio is, or whether it is interlaced or How is the line, color fidelity, etc., and this information is also an important reference to measure the performance of a high definition network camera.
Therefore, HD network cameras that meet HDTV720p/1080i/1080p standards will undoubtedly become mainstream.
Who will dominate MJPEG and H.264 video encoding for HD webcams?
Video encoding is a key parameter of HD network cameras. It determines the image quality of the transmitted video and the required network bandwidth. The HD video camera video coding standards we currently see are mainly MJPEG and H.264.
MJPEG (Motion JPEG) is a dynamic image compression technology developed on the basis of JPEG. It only compresses a certain frame, but basically does not consider the changes between different frames in the video stream. Through this compression technology, high-definition video images can be obtained, and the video definition and compression frame number of each channel can be flexibly set, and the compressed image can also be arbitrarily edited. However, its defects are also very obvious: First, there are serious drop frames and poor real-time performance. Under the premise that each path must be high-definition, it is difficult to complete real-time compression; Second, compression efficiency is low, and transmission bandwidth and storage space occupy a large area. .
H.264 is the next-generation video coding standard developed by the joint video work group JVT jointly established by ITU-T and ISO. It is used to achieve high compression ratio, high image quality, and good network adaptability. H.264 not only saves more than 80% of code rate than MJPEG, but also has better support for network transmission. H.264 introduces an encoding mechanism for IP packets, which facilitates packet transmission in the network, supports streaming media transmission of video in the network, and supports hierarchical encoding transmission under different network resources, thereby obtaining smooth image quality. H.264 can achieve broadcast-quality HD video resolutions of 720p and 1080i/p at lower bandwidths.
Although MJPEG can obtain relatively good single-image quality, due to its fatal flaws in terms of sportiness, bandwidth occupation, and storage space occupation, HD network cameras will inevitably rely mainly on H.264.
Can a HD Network Camera fully represent HD surveillance?
For high-definition, there is an important obstacle to really replacing SD, which is how to ensure the integrity of the solution at a low cost. According to the characteristics of traditional monitoring applications, high definition only makes sense when covering front-end, center management, video storage, decoding and display. At present, all the HD products that we see are only at the front end, namely HD network cameras. The back-end management, storage, and decoding are not available, and they cannot be fully promoted.
Therefore, for high-definition surveillance, only high-definition network cameras are not enough. High-definition webcams merely complete front-end functions, and more comprehensive HD applications require the cooperation of a series of back-end parts. Kodak took the lead in this year's Full HD series of products and solutions released at the end of 2009. It provides users with complete end-to-end high-definition monitoring through the full cooperation of high-definition network cameras, high-definition NVRs, high-definition video walls, and high-definition clients. Solution, while ensuring the system's cost-effective.
Summary With the rapid development of high-definition surveillance, various concepts related to high-definition cameras emerge in endlessly. Through the series of problems mentioned above, no matter how these concepts are overwhelming, we can maintain clear ideas and make accurate judgments.