How everything began

Historically, CCD (Charged Coupled Device) sensors have existed much longer than CMOS sensors, that is to say, for more than 40 years. Due to constant improvement and optimization over the years, CCD sensors today stand for excellent image quality. In 2009, the American scientists Willard Boyle and George E. Smith were awarded the Nobel Prize for Physics for the invention of the CCD sensor. Originally developed in 1969 for the storage of data, the potential of the Charge Coupled Device as a light sensitive apparatus was soon realized. By 1975, the first sensors with a resolution sufficient for television cameras appeared. However, it took more than 10 years before the process technology was mature enough to begin production of CMOS (Complementary Metal Oxide Semiconductor) sensors. In the mid-nineties, the first commercially successful CMOS sensors appeared on the market. Source: www.asmag.com

The more sensitive the better

CMOS sensors are based on the same physical principles as CCD sensors. They convert incoming photons into electrons by means of a photo effect. As a result of their sensor structure, the maximum sensitivity of CMOS sensors is in the red spectral region (650 – 700 nm). CCD sensors, not least because of the numerous innovations during their longer technological history, have a maximum at about 550 nm – exactly where the human eye is most sensitive. For a variety of technical reasons, CMOS sensors in the past were considerably less efficient in converting the incoming light to an electrical signal. The photosensitive area within each pixel in a CMOS sensor occupied only a fractional part of the total pixel area. The rest of the pixel area was populated by the individual readout electronics associated with each photosensitive area. The structure of CCD sensors is different. In CCDs, the electronics for the evaluation of the charges collected by the sensor surface is located outside of the chip, so almost the entire chip surface is available for photosensitive structures.

Over the last few years, design improvements have increased the size of the light sensitive area of CMOS sensors to near the level of CCD sensors. One example of such an improvement is the micro-lens array that is now applied to the CMOS chip. The lens array collects the light impinging on each pixel area in the CCD sensor and focuses it on the available light sensitive region within the pixel.

The price of individuality

One set of electronics for all pixels – this phrase regarding processing capability is valid for CCD sensors and at first sight, sounds rather like a trade-off. But in fact, it is an advantage for image quality. Because there is one common electronic path for a large fraction, if not for all, of the pixels in a CCD chip, all analog pixel signals are evaluated and processed in the same way and they are all converted to digital signals in the same way.

CMOS chips carry individual processing electronics on board each pixel and are different in this respect. This characteristic means that they can be read out faster and that the image area can be accessed in more flexible ways. However, there are tiny variations within the individual electronic structures used to process each pixel, and this means that signal offset can differ from pixel to pixel within a CMOS sensor, although the amplification slopes are almost identical. Variations between the offset values of the pixels in a CMOS sensor are typically ten times larger than those of CCD sensors.

Taken together, this offset variation represents a difficulty with respect to the sensitivity threshold of the sensor. This is especially true when a weak signal that is slightly greater than the background noise must be detected. In this situation, a CMOS sensor looks worse than a CCD sensor. By definition, this threshold is reached when the signal from the sensor is as high as the noise (i.e., the signal-to-noise ratio or SNR equals one). A technical term that quantitatively describes this characteristic is known as the Fixed Pattern Noise (FPN). CMOS sensors exhibit a higher FPN than CCD sensors.

Less sensitivity, but lots of space for electrons CMOS sensors, however, do score much better in another area – they can provide a higher full well capacity. The full well capacity represents the maximum number of electrons that an individual pixel can hold. On CCD sensors, this number is often artificially limited to a reduced saturation capacity to avoid certain technical problems. The ratio of the saturation capacity (full well capacity, respectively) to the sensitivity threshold determines the sensor’s dynamic range. In comparison to a CCD sensor, a CMOS sensor wins with regard to the saturation capacity what it loses when it comes to low-light sensitivity. As a result, CMOS and CCD sensors have almost the same level of dynamic range. Certain procedures can be used to modify the characteristic response curve of a sensor so that it matches what a human eye perceives. This is especially true for CMOS sensors, and therefore a logarithmic behavior with a dynamic range of more than 100 dB can be achieved. This modification differentiates dark regions within an image more precisely than bright regions and should be applied with care.

The saturation capacity is related to a second important parameter of an imaging device, the maximum signal-tonoise ratio. This parameter quantifies the ratio of a signal associated with light under optimum conditions to pure sensor noise without any light exposure. It can be shown, that in principle, the maximum signal-to-noise ratio equals the square root of the saturation capacity. Thus, the CMOS sensor excels with respect to the maximum signal-to-noise ratio, but it needs more light to do so.

As a simplified rule-of-thumb, one can say that CCD sensors are the preferred choice for applications with little light and CMOS sensors are a good alternative when there is a lot of light.

It can become too bright for a sensor

If especially bright light is present, users must sometimes struggle with other effects. When a CCD pixel is overexposed to light, the pixels can generate an excess of electrons that can migrate into neighboring pixels. In this situation, very bright image structures seem to extend into the darker structures, an effect known as “blooming”. CMOS sensors don’t see the migration effect and are not prone to blooming like that.

After a CCD sensor has been exposed to very bright light, the charge transportation process can cause bright stripes to appear in the image. The bright structures within the image appear as white smeared lines. This effect is known “smearing” and can be seen, for example, in images acquired at night when a car approaches the camera with its headlights on. As with blooming, CMOS sensors have an advantage compared to CCD sensors because they do not exhibit smearing.

Small bad habits and how they are moderated

For technical and cost reasons, quite a large number of commercially available cameras with CMOS sensors implement a rolling shutter. With this image acquisition method, all of the lines in a sensor are not read out of the sensor at a single instant in time. Instead, there is a time lag between the start of readout for each line in the frame.

In cameras with a global shutter, exposure is started for all pixels at the same time and is stopped for all pixels at the same time. In cameras with a rolling shutter, exposure is started sequentially line by line and is ended sequentially line by line. With rolling shutter technology artifacts can occur, particularly with rapid moving objects (unwanted, for instance, in intelligent transportation systems). These days, other CMOS sensor technical inadequacies can easily be compensated for within the camera. This includes non-uniformities that appear during the conversion of charges to gray values (ADC inequality) or that result from variations in the electrical properties of the numerous individual readout structures used in a CMOS sensor. Defective pixels can be corrected by interpolation in the camera. In addition to correcting the inadequacies already mentioned for CMOS sensors, the electronics in today’s cameras can also correct for the irregularities exhibited by CCD sensors.

The agony of choice

CMOS sensors have a shorter history than CCD sensors, but they are now technically mature and even represent the best choice for some applications. Even novelties such as backside illuminated sensor technology (BSI), which was first introduced for CCD sensors, are currently entering the CMOS world. With this technology, the photosensitive area in each pixel is increased because no electronics are obscuring the pixel area.

But when you must choose the optimum solution of a specific task, many of the aspects mentioned in this article will come into play. In the end, the constraints and the details of your application should determine which sensor technology represents the best alternative.

HD analog is quickly becoming the mainstream of analog video. By 2018, over 90% of analog cameras will be HD analog (according to 2016 IHS report). Dahua led the industry to introduce HDCVI Technology in 2012, and continues to enhance the technology leadership by bringing state of the art performance in terms of resolution, light sensitivity, intelligence and usability to the HDCVI community. The comprehensive offering of HDCVI matches up very well to the IP equivalent. Customers can choose the most suitable system for their sites without being constrained to IP only. The emergence of multi-mode DVR, which records video from HDCVI, TVI, AHD, CVBS and IP cameras, makes it very easy to upgrade a site by increment.

Future development of HD analog must fit the needs of IoT and big data applications, which is driving the value of security systems in the next few years. AI (Artificial Intelligence) Deep Learning will be a key technology component to enable this to happen.

Enter a New Era – HDCVI 4.0

Dahua is introducing HDCVI 4.0 technology framework, with 3 key components: 4K-HDCVI for superior video capture, IoT-HDCVI for multi-dimensional sensing and AI-HDCVI to transform HDCVI-video into searchable Boolean data. New products will be introduced throughout the year in 2017 to enhance the user experience of HDCVI customers. The HDCVI community can expect a lot more opportunities to use HDCVI technology to expand security application space.

Dahua 4K-HDCVI adopts 4K Ultra HD image acquisition and back-end DVR storage. HDCVI technology architecture overcame the common bottleneck of transmission bandwidth to achieve high resolution video previously only available on IPC. This is a major breakthrough to extend the potential of HDCVI in future. Dahua IoT-HDCVI technology, combining with IoT sensing technology, enables cameras to surpass basic function of providing video information. Utilizing IoT sensors, coaxial cables are capable of transmitting not only video signal, but also information such as alarm, temperature and humidity. HDCVI technology architecture supports complex data transmission between camera and DVR, and makes it possible for multi-dimensional sensing camera and DVR to form an IoT solution. The near real-time transmission of HDCVI also improves the responsiveness of IoT applications. Dahua AI-HDCVI technology integrates HDCVI video and audio with AI (Artificial Intelligence) Deep Learning. AI-HDCVI performs near-human level accuracy in image classification and voice recognition to transform HDCVI video and audio into searchable Boolean data. The output of these analysis could solve resource allocation problems for example, in the retail industry with customer and or in the management of city transportation with vehicle traffic analysis.

The scalable and expandable architecture of HDCVI enables future-proof products and solutions to be developed. It protects customers’ investment by allowing seamless upgrade to new technologies as they emerge. Dahua HDCVI 4.0 comprises of 4K-HDCVI, IoT-HDCVI and AI-HDCVI leads the industry into a new era of higher resolution, more intelligent and convenient.

Dahua Technology Brings HDCVI into the 4K Era, a Brighter World

4K-HDCVI is the first product launched by Dahua Technology in 2017. While the industry is trying to break through the bandwidth constraint of coaxial cable transmission, Dahua releases the first 4K Ultra HD solution by deploying superior signal modulation mechanism and noise reduction technique. It transmits 4K video signal up to 700m (RG6 cable). Dahua 4K-HDCVI offering includes 4K box camera, 4K IR bullet& dome camera, 4K fish-eye panoramic camera, 4K multi-sensor 180 degree panoramic camera, and a series of 4K supported XVR (multi-mode DVR). Dahua4K-HDCVI offering delivers 3840(H) x 2160(V) ultra-high resolution images, equivalent to 4X 1080 HD camera’s, to achieve wide angle coverage and clear video evidence at the same time.

All HD analog technologies, limited by the data transmission capacity of coaxial cables, were not able to provide 4K resolution. Dahua Technology, leveraging on our superior signal modulation mechanism and noise reduction technique, developed TX &RX chipsets autonomously to break through this limitation. Dahua 4K-HDCVI products are capable of ultra-distance transmission:

– RG6 coaxial cables for 700m video and audio lose-less transmission

– RG59 coaxial cables for 500m video and audio lose-less transmission

– UTP Cat 6 network cable for 300m video and audio lose-less transmission

The New 4K XVR recorder is compatible with all existing HDCVI/HDTVI/AHD cameras, meanwhile, it also supports CVBS and IP cameras. All these make upgrading to 4K much more convenient and cost-effective. The installation, configuration, operation and maintenance of 4K HDCVI are the same as before, preserving the plug & play convenience of analog video system. Once your existing DVR is replaced by a new 4K XVR, you can simply replace the existing camera with 4K camera or add 4K camera as you go.

DH-HAC-HF3805G, adopts the SONY 4/3” 8MP STARVIS sensor, is able to output 3840(H) x2160(V) ultra HD images with impressive night performance due to the bigger size sensor. It is also the first HD analog camera to utilize M43 mount lens in the security industry which brings the rich selection of M43 lenses to customers. Users can choose their preferred lens based on different scenarios. This camera also delivers functions like autofocus, image magnification for dynamic detection and a linkage alarm without the need to use with the back-end. All the settings and functions can be easily controlled by the OSD menu, and use together with applicable housing, this camera is good for outdoor surveillance. DH-HAC-HF3805G is truly THE camera for high performance surveillance under poor illumination.

Another star product is the DH-HAC-PFW3601, which is the first HD analog multi-lens infrared camera with a 4K 180 degree panoramic view. This star product makes use of Dahua’s advanced image stitch algorithm to perform 180 degrees panoramic seamless stitching. It can be controlled by the OSD menu and easily operated. By using three SONY STARVIS sensors and F1.4 large aperture lens, this infrared camera delivers high quality images even under low light. It also outputs panoramic seamless stitching images and 3 single-lens images. Working with the 4K XVR, panoramic images can set up an electronic cruise model to realize a multiple target split-screen view using the magnifying tracking function. It will benefit the detection of moving targets in critical areas. In addition, the camera has IP67 and IK10 protection, making it a good choice for important entrances and exits area, city transportation junctions, and parks.

Summary

4K-HDCVI, IoT-HDCVI and AI-HDCVI are going to increase the potential market space of HD analog and protect the investment of HDCVI customers. New products will be introduced throughout the year in 2017 to implement the HDCVI 4.0 framework. Follow us on LinkedIn, Facebook to get first-hand information on new product releases.