When it comes to HD surveillance, high-quality images are a prerequisite for HD and a prerequisite for the development of video surveillance. For example, in a crowded subway station, whether you can clearly see a person’s facial features, and whether the license plate of a fast-moving highway can be discerned, etc., all need clear images. To see more clearly, you must rely on the image quality that the front-end camera can provide. The disadvantages of SD cameras are that the picture is blurred and the resolution is low. When an unexpected event occurs and the video playback needs to be viewed, the details of the event scene are difficult to distinguish and cannot provide effective information. In contrast, high-definition cameras can bring higher pixels, a wider monitoring range, and higher resolution, which quickly improves the quality of traditional video surveillance.
Of course, high-definition monitoring is a unified whole, involving multiple links of the monitoring system, including front-end video capture, intermediate video transmission, and back-end high-definition storage, display, analysis, linkage, etc. Due to space limitations, this article only discusses how to ensure the collection of high-definition information in the front part.
CMOS is more suitable for the HD
The sensor is the core component of the camera and determines the image quality. The image of the subject is focused on the sensor chip by the lens, and the sensor processes it according to the intensity of light to form a video signal output. CCD and CMOS are two types of image sensors currently widely used. Both use photodiodes to perform photoelectric conversion to convert images into digital data. The main difference is that the digital data is transmitted in different ways. In terms of performance, they are mainly reflected in sensitivity, noise processing, and power consumption. In the comparison of sensors of the same size area, the resolution of CCD is generally much higher than that of CMOS. Therefore, the low-illumination SD cameras commonly used in the market basically use CCD technology as their own sensing equipment. In the SD era, CCD is undoubtedly more popular than CMOS.
The manufacturing process of CCD is complicated and it is only in the hands of a few manufacturers, which leads to high manufacturing costs. Each time the CCD size increases, the cost increases geometrically. Therefore, if the monitoring is to be high-definition, the development prospect of CCD is obviously limited. CMOS is characterized by its low cost and low power consumption. With the same number of pixels, the price is lower, and it has a high cost performance. It can continue to develop towards higher pixels and higher resolutions, and HD surveillance is very cost sensitive. Therefore, most HD cameras on the market use CMOS.
To achieve high-definition, technical cooperation is also needed in wide dynamics, automatic white balance, image sharpness, and digital noise reduction, color adjustment, and light compensation. Only when these comprehensive performances can be well reflected and they can coordinate with each other, can it be said that the high-definition is truly realized. The combination of CMOS and other image processing technologies far exceeds CCD, with higher dynamic range and faster response speed, which is more suitable for the large data volume characteristics of high-definition monitoring. In addition, with the development of technology, the sensitivity of CMOS has also been greatly improved. In effect, some CMOS sensors are now comparable to CCDs.
HD camera requires HD lens
Security’s high-definition surveillance not only requires high-definition video cameras but also professional lenses. HD lenses are of great significance for HD surveillance. Camera definition in the HD era can reach millions of levels, but if the lens is not matched with it, the ultra-high resolution effect of the camera cannot be fully displayed.
In the case of the same camera, the final performance of the picture and the resolution of the lens play a decisive role. High-definition lenses are superior to ordinary lenses in three aspects: sharpness, spectral transmission ability, and spectral correction ability. High-definition lenses can enhance the contrast and brightness of the picture, obtain high-definition image effects, and show richer details on the picture.
So how do you choose a high-definition lens? Generally speaking, when selecting a lens, you must choose the same or higher lens product according to the highest resolution of the camera. In addition, specific analysis should be made according to the characteristics of the project. For example, in places that need to shoot at night, in order to make day and night cameras have better shooting effects, you must rely on the HD lens with a larger aperture, such as 2/3 inches, and a better aperture value F, so that the camera can obtain More light flux helps the camera to get better shooting effect at night.
In some projects, the camera needs to be equipped with an infrared fill light, so you should use a lens with IR function, so that you can get a brighter picture at night, and reduce the problem of blur at night. For more demanding environments, such as the use of laser lights to monitor long-distance targets, it is necessary to ensure that the invisible light wavelength can still reach a transmittance of more than 60% at 900um.
The role of video processors cannot be ignored
To achieve clear image quality, in addition to the processing of light by the front lens and sensor, the image processing is also a part of the camera that cannot be ignored. The images obtained directly from the sensor are often unsatisfactory. Both the color and the details are far from the actual image, which is difficult to use as evidence after the fact. After image processing, including face detection, noise filtering, removing dead pixels, skin color correction, automatic white balance, automatic exposure, and edge enhancement, etc., the image can be made more delicate and closer to the real world image. So what kind of processor is used will directly affect the monitoring effect.
At present, many high-definition cameras directly use ISP or integrated CMOS (built-in ISP image processor) provided by CMOS manufacturers. These ISP image processors can cope with general scenes, but the processing effect is poor for scenes that require wide dynamics. However, the monitoring system is different from consumer electronics or broadcasting applications. In a video surveillance system, the monitored object cannot match the angle of the camera. Therefore, in the case of backlight and backlight, ordinary ISP image processors cannot provide effective wide dynamic images. , Resulting in a reduction in the quality of the visible image.
In the high-definition era, the processor not only carries a lot of work such as image processing and analysis, codec compression, etc., but also embeds a large number of intelligent analysis algorithms to analyze massive high-definition data, which plays a more important role.
In addition, the video processor not only supports multi-format decoding, multi-rate multi-stream and high-definition multi-channel functions, but also provides audio, voice and other high-definition video editing, which can achieve higher flexibility and lower design complexity. The video processor supports a full range of products from D1, 720p to 1080p up to 30 frames per second, so that customers can build a scalable product line to support a variety of editing. The ISP software implementation provides functions such as video stabilization, face detection, noise filtering, automatic white balance, automatic exposure, and edge enhancement.
Image compression cannot be underestimated
In view of the current development status of storage devices, when large-capacity hard disks are still expensive, the original images must be compressed in order to reduce storage and broadband costs. Although the higher the compression ratio, the more blurred the image is, but if the recording capacity per hour reaches several G, it is difficult for customers to accept. Under the same conditions of the chip, the algorithm plays a key role. In order to reach an equilibrium point, good manufacturers use the H.264 algorithm. H.264 can achieve 720p and 1080p broadcast-quality HD video resolutions at lower bandwidths. At the same image quality level, the bit rate comparison of a 115-second video stream under different video standards. Without motion compensation, the H.264 encoder is at least 3 times more efficient than the MPEG-4 encoder and 6 times more efficient than the M-JPEG encoder.
With the same image quality, compared with the traditional compression technology, a video surveillance system that supports the H.264 compression standard can reduce storage costs and bandwidth consumption by at least 50%.
With the increasing scale of the system and the increasing demand for high-resolution images and high frame rates, this efficient compression technology will likely drive megapixel cameras with the highest speed in the applications that require high resolution and high frames. Monitoring sites such as airports, retail stores, banks and entertainment venues.
High-definition camera series support H.264 format, large-scale compression of large files without affecting the image quality, to obtain higher frame rate and image resolution, which can output higher quality images. The HD camera also provides intelligent image cropping technology, which can avoid some unimportant pictures on the sensor, and large images can be cropped in the horizontal and vertical directions. Allows only the required data to be transmitted and stored. Discarded data can reduce the use of a large amount of storage space and bandwidth, providing strong support for overall high-definition monitoring.
It can be said that whether it can win in the fierce competition of video surveillance lies in keeping up with the trend of high definition. The choice of HD front-end is the first step. The quality of the front-end directly affects the monitoring effect. Judging from the actual use results, with the same back-end monitoring solution, what is spelled is the high-definition of the front-end collected information. The high-quality image provides a solid foundation for real-time monitoring, screen transfer, detailed browsing, and intelligent analysis, which greatly enhances the application value of the system.