Significance of parameters of wide dynamic low illumination camera

Significance of parameters of wide dynamic low illumination camera

Wide dynamic technology is a technology used to let the camera see the image features in a very strong contrast.

When the high-brightness area is irradiated by a strong light source (sunlight, lights or reflections, etc.). ) and shadow, backlight and other areas with relatively low brightness coexist in the image. The bright areas will turn white due to overexposure, and the dark areas will turn black due to underexposure, which seriously affects the image quality. The performance of the camera is limited to the brightest and darker areas in the same scene, which is commonly called "dynamic range".

Generalized "dynamic range" refers to the span that a changing thing may change, that is, the area between the lowest pole and the highest pole of its changing value, which is generally described as the difference between the highest point and the lowest point. This is a very widely used concept. When talking about the shooting image index of camera products, the general "dynamic range" refers to the adaptability of the camera to the illumination reflection of the scene, specifically the range of brightness (contrast) and color temperature (contrast).

Compared with the traditional 3: 1 dynamic range camera, the wide dynamic camera has exceeded several times. Natural light is arranged in the starry night 120000 lux to 0.00035Lux. When the camera looks out of the window from indoors, the indoor illumination is 100Lux, the outdoor illumination may be 10000 lux, and the contrast is10000/100 =100/. This contrast is easy for human eyes to see, because human eyes can handle the contrast of 1000: 1. However, the traditional closed-circuit surveillance camera will have great problems when dealing with it. Traditional cameras only have a contrast ratio of 3: 1, so we can only choose to use the electronic shutter of 1/60 seconds to get the correct exposure of indoor objects, but the outdoor images will be cleared (all white). Or to put it another way, the camera chooses 1/6000 seconds to get the perfect exposure of the outdoor image, but the indoor image will be cleared (all black). This is a defect that has existed since the invention of the camera.

Modern traffic needs modern traffic management. In order to solve the traffic congestion and congestion at major urban sections and intersections, and reduce accidents and violations, it is necessary to establish a modern intelligent traffic command and control system. At the same time, it is also of great significance to improve the city image and promote the development of urban civilization. The overall goal of the system design is to monitor the traffic flow and operation through road monitoring, to control the traffic in key sections in real time, to find all kinds of anomalies in time and to take emergency measures, to ensure the high-speed, safe and effective operation of roads and to improve the traffic level of modern life. According to the actual needs of traffic monitoring, controllable cameras or fixed cameras are usually installed at traffic intersections, stations, commercial areas, highway toll stations and other key parts. After analyzing the special requirements of road monitoring, this paper mainly puts forward some suggestions on the selection and design of road monitoring cameras.

Matters needing attention in purchasing road monitoring cameras

In the video control system, the performance of the system equipment is the key factor to evaluate the success of the system, whether from the front-end image acquisition or the back-end image signal recording, display and control. There is no doubt that the choice of equipment directly affects the stability and reliability of the system, image quality, service life of the system and other issues, which is related to the investment interests of builders. Therefore, system equipment selection is an important link throughout the whole design process.

Demand analysis of camera in road monitoring system.

There is a high demand for image clarity and real-time, and it is required to see the license plate clearly. If you can't clearly confirm the license plate number, it is meaningless to monitor the capture. Because road monitoring needs to work 24 hours a day, it is necessary to obtain high-quality pictures in extremely dark conditions. The dynamic range of outdoor street lamps changes greatly, and the ambient illumination reaches 50000lx-10000000lx in summer sunshine. At night, the street lamp is only 0. 1Lux, which changes greatly. In this case, no matter whether the camera has the function of automatically adjusting the sensitivity, it is impossible to adapt to such a wide illumination range through the electronic shutter of the camera itself, and it is also impossible to control the image effect. Therefore, the camera must be required to have a wide dynamic range. When shooting in poor lighting conditions, the dynamic images will inevitably have noise interference. All wide dynamic cameras are required to have outstanding denoising function for dynamic images, which can eliminate shadows and tails of images.

Selection basis of road monitoring camera

The core integrated circuit of wide dynamic camera performance is CCD sensor chip. The working principle is that the target scene is imaged on the CCD sensor through the CCD optical lens, and the sensor is a high-sensitivity CCD, and then 50 fields are 25 frames per second (CCIR system 25 frames per second; NTSC standard 30 Frame/s) image, the signal output by CCD is processed by CDS correlation sample-and-hold circuit, AGC and A/D conversion circuit, and then the image stored in the memory is read out line by line by using high-speed operation chip and data processing function to form a complete video signal. Therefore, the quality of camera output signal is not only the choice of CCD sensor with good performance, but also the choice of data processing chip/circuit.

After summarizing many years of practical experience, the equipment integration and engineers of road traffic monitoring chose the following cameras:

High line number industrial standard camera (500-540 TV line). Low illumination (≤0. 1lux), the minimum illumination reaches 0.0lux, and clear image effects can be obtained even in the case of low illumination at night. Super-sensitive, large-size CCD (generally 1/2-inch CCD) is adopted. Because the target size of 1/2 "camera is larger than that of 1/3" camera, the imaging effect is better. (large imaging area; Large luminous flux and low illumination requirements. ) has the ultra-wide dynamic shooting function, and can respond quickly and accurately in the case of Gao Fancha and sudden light changes, so as to obtain high-quality and fully exposed images. Using super noise reduction technology, dynamic image noise, image shadow and tailing can be eliminated. Especially when solving the problem of road traffic monitoring or parking lot monitoring caused by headlights, low tailing degree is particularly important. High signal-to-noise ratio, fast white balance automatic adjustment and other functions (shutter speed can not be slower than11000 seconds) camera. Adopt industrial-grade equipment, with good all-weather working ability and long-term stable and reliable operation. This paper aims to explain the following key parameters.

1/2 EXVIEW HAD？ Charge coupled device

Ccd products have been produced for more than 30 years, from 200,000 pixels at that time to 5-8 million pixels now. Both the market scale and the application field have made great progress, which can be said to be steadily and gradually improved, especially in the field of consumption in recent years.

Compared with the initial development, the area of each pixel of the current ccd module has been reduced to below110. In the future, under the requirements of miniaturization and high pixel of application products, the unit area will be smaller. At the same time of miniaturization, using various newly developed technologies, the reduction of unit area will not affect the sensitivity, and at the same time, it is required to maintain or improve its performance.

Let's briefly introduce the ccd sensor developed by Sony according to the age division:

1, with sensor

Had(hole-accumulation diode) sensor is a unique structure of Sony. A positive hole accumulation layer is added on the surface of N-type substrate, P-type and n+2 electrode. Due to the design of this positive hole accumulation layer, the common dark current problem on the sensor surface can be solved. In addition, a vertical tunnel is designed on the N-type substrate to allow electrons to pass through, which improves the aperture ratio, in other words, improves the sensitivity. In the early 1980s, Sony took the lead in using it in variable-speed electronic shutter products, and it can also get clear images when shooting fast-moving objects.

2. On-chip microlens

In the late 1980s, due to the shrinking of each pixel in ccd, the light receiving area will be reduced and the sensitivity will be lower. In order to improve this problem, Sony installed a micro lens in front of each photodiode. After using the microlens, the photosensitive area is not determined by the opening area of the sensor, but by the surface area of the microlens. Therefore, the aperture ratio is improved in specification, and the brightness is also greatly improved.

3, super ccd

Since the late 1990s, the unit area of ccd has become smaller and smaller, and the microlens technology developed by 1989 has been unable to improve the brightness. If the magnification of the internal amplifier of ccd module is increased, the noise will be improved and the image quality will be obviously affected. Sony has gone further in the research and development of ccd technology, improved the technology of using tiny lenses in the past, improved the utilization rate of light, and developed the technology of optimizing lens shape, that is, Sony super had ccd technology. Basically, the brightness is improved by improving the utilization efficiency of light, which also lays the foundation for the current basic ccd technology.

4. New structure ccd

With the continuous improvement of the F value of the camera optical lens, more and more oblique light enters the camera, which makes the light incident on the ccd module unable to focus on the sensor 100%, and the sensitivity of the ccd sensor will be reduced. 1998 In order to improve this problem, Sony added an inner lens between the color filter and the shading film. After adding this layer of lens, the internal light path can be improved, so that oblique light can also be focused on the photoreceptor. At the same time, the insulating layer between the silicon substrate and the electrode becomes thinner, so that the signal that will cause vertical ccd image noise will not enter, and the smear characteristics are improved.

5. exview has ccd.

Infrared light with longer wavelength than visible light can also be photoelectric converted in semiconductor silicon chips. But so far, ccd can not effectively collect these photoelectric converted charges into the sensor. Therefore, Sony's newly developed "exview had ccd" technology in 1998 can effectively convert the near-infrared light that has not been effectively used before into image data for utilization. So that the visible light range is expanded to infrared light, and the brightness can be greatly improved. When using "exview had ccd" module, you can get high-brightness photos in dark environment. Moreover, in the process of photoelectric conversion in the deep layer of silicon wafer, the trailing components leaked to the vertical ccd can also be collected in the sensor, so the noise affecting the image quality will be greatly reduced.

minimum illumination

Illuminance is a unit that reflects the intensity of light, and its physical meaning is the luminous flux per unit area. The unit of illumination is lumens per square meter, also called lux: 1 lux = 1 lm/ square meter. In the above formula, Lm is the unit of luminous flux and is defined as the melting temperature of pure platinum (about 178).

In order to have a perceptual understanding of the amount of light, let's give an example to calculate it. A 100W incandescent lamp emits a total luminous flux of about 1200Lm. If the luminous flux is assumed to be uniformly distributed on a hemisphere, the illuminance values at the distance of 1m and 5m can be obtained as follows: the hemisphere area with the radius of 1m is 2π×12 = 6.28m2; The illuminance value at the distance from the light source 1m is1200lm/6.28m2 =1965438. The hemisphere area with a radius of 5m is 2π× 52 = 157m2, and the illumination value at a distance of 5m from the light source is1200lm/157m2 = 7.64lux..

It can be seen that the illumination from a point light source obeys inverse square law. 1LUX is approximately equal to the illumination of 1 candle at the distance of1m. The lowest illumination we often see in the camera parameter specification means that the camera can only get a clear image under the marked lux value, and the smaller the value, the better, indicating that the higher the sensitivity of CCD. Under the same conditions, the illumination required by a black-and-white camera is 10 times lower than that of a color camera that still has to deal with color density. The sensitivity of black-and-white cameras is about 0.02-0.5lux (lux), and most color cameras are above 1lux. The illuminance value is not only related to the aperture size (F value) of the lens, but also related to the surrounding environment during the test. In terms of aperture size (F value), the larger the aperture, the smaller the F value and the lower the required illumination. 0.97lux/F0.75 is equivalent to 2.5lux/F 1.2 is equivalent to 3.4lux/F 1.0.

Reference environment and lighting:

Approximate illumination of reference environment

100000lux in summer sunshine

Indoor fluorescent lamp 100lux

Cloudy outdoor 10000lux

10lux indoor dusk

Television studio? 1000lux

20cm candle 10- 15lux

60cm away from the 60w desk lamp? 300lux

Street lamps at night? 0. 1lux

Cameras can be divided into

Ordinary type: the illumination required for normal operation is 1~3lux.

Moonlight type: the illumination required for normal operation is about 0. 1lux.

Starlight type: the illumination required for normal operation is below 0.0 1lux.

Infrared type: Illuminated by infrared lamp, imaging can be performed without light.

The minimum illumination of a wide dynamic camera means that when the brightness of the shot scene is low to a certain extent, the amplitude of the video signal output by the camera drops to 50%-33% of the standard amplitude of 700mV (the nominal video value is 1V and the standard value is 700 mv); The other lowest illuminance is the illuminance on the CCD, which is the sensitivity of the CCD. The illuminance value of CCD is much lower than the minimum illuminance value of camera, so many unscrupulous merchants mark the minimum illuminance value of CCD as the minimum illuminance value of camera to deceive people who don't know, especially in some OEM products and some low-end camera products in China.

The evolution of low-light cameras in the market can be simply divided into the following three steps: color/monochrome); During the day; Low speed shutter (SLOW/SHUTTER) and ultra-sensitive camera (EXVIEW HAD).

1. daytime color/nighttime black and white (daytime and nighttime camera color/monochrome)

At present, this kind of camera still has its specific demand group in the market. Color/monochrome cameras take advantage of the high sensitivity of black and white images to infrared rays. Under certain light source conditions, it changes the image from color to black and white by line switching, thus matching infrared rays. In the technical evolution of color/black-and-white line conversion, two sensors (1 color and 1 black-and-white) * * were used to switch again with a set of circuits. At present, this camera has adopted a single CCD (color) design, which is a color camera during the day or when the light source is sufficient. When the night falls or the light source is insufficient (generally at 1Lux ~ 3Lux), digital circuits are used to eliminate color signals and turn them into black and white images. In order to cooperate with infrared, the indispensable infrared filter of color camera has also been removed. Although this method can achieve the purpose of "low illumination" at night, it has the disadvantages of blurred images and unnatural colors during the day, and the shooting distance of the camera will be limited by the irradiation distance of the infrared lamp. However, it is still controversial whether color/monochrome cameras belong to "low illumination" cameras. Experts pointed out that the real "low-light camera" should refer to the functions that the camera itself (the components and technologies used) can realize, while the color/black-and-white camera in the daytime cannot change itself due to the sensitivity of CCD, and it can't be regarded as a low-light camera.

2. Slow/Shutter

This kind of camera is also called (picture) accumulation camera. By using computer storage technology, several blurred pictures are continuously accumulated into clear pictures. By using slow shutter technology, the illumination of the camera is reduced to 0.008 lux/f1.2 (× 128), and the cumulative number of frames is (128). This low-light camera is suitable for museums that prohibit the destruction of red and ultraviolet rays, biological activity observation at night, military coastline monitoring at night, etc. And the monitoring of static places. Most of these low-light cameras are imported brands, which are expensive and have few cumulative frames (32 frames).

3. Ultra-sensitive camera (EXVIEW/HAD)

EXVIEW/HAD, also known as 24-hour camera, is 1998, the most popular model in the world. Its color illumination can reach 0.05LUX, black and white can reach 0.003-0.00 1LUX (it can also reach 0LUX with infrared rays), which not only can clearly identify the image, but also is a real-time continuous image. This kind of camera mainly adopts EXVIEW/HAD/CCD (extrasensory CCD) introduced by Sony Components Factory 1997. It uses patented technology to improve the aperture ratio of each pixel of CCD, so as to meet the requirements of lower illumination. The emergence of this technology has been welcomed by the monitoring market, and it can show the best effect in all lighting environments. Especially in the near-infrared region of 760mm- 1 100mm, high-definition black-and-white images can be obtained by special infrared lighting equipment, and the monitoring of 0 illumination (no light at all) can be realized. If infrared illumination with appropriate wavelength is used, clear black-and-white images can be obtained.

Samsung TECHWIN Company (formerly known as Samsung Airlines, known as Sanxingguang Electronics in China) has always stood at the forefront of technological innovation by virtue of 30 years of industry production experience, providing customers with high-quality security products. Its product series include SHC-740, SHC-740, SHC-72 1, SDZ-330, SPD-3300, etc. All of them adopt 128 times frame accumulation technology, and the definition is more than 520TVL, and the signal-to-noise ratio is more than 50db, with the function of day-to-night conversion. Especially SHC-740 (figure 1) adopts EX-VIEW HAD CCD and Samsung SVⅲDSP chip. In terms of low illumination technology, HD has made a new breakthrough (up to 540TVL), which enables the camera to obtain high-quality images even in almost all black conditions, and its minimum illumination color mode is 0.0 1lux @ F65438. Sens-up mode is 0.0003 LUX@F 1.2, which is widely used in national defense, frontier defense, army and expressway.

Wide dynamic

In some cases where the contrast between light and dark is too large, the general camera is limited by the photosensitive characteristics of CCD, and the images taken often have too bright background or too dark foreground. In view of this situation, wide dynamic technology came into being and solved this problem well. Prior to this, traditional cameras generally used backlight compensation function to adapt to the situation of large light contrast.

When the objects in the field of view of conventional cameras have high brightness background light, it is necessary to look at the objects at the door or outside the window. Usually, the central backlight compensation (BLC) mode is adopted, which mainly depends on improving the brightness of the central part of the field of view and reducing the brightness of the surrounding parts of the field of view to see the objects in the central position clearly.

Backlight compensation, also known as backlight compensation, is to divide the picture into several different areas, and each area is exposed separately. In some applications, the field of view may contain very bright areas, the included subject is surrounded by bright fields, and the picture is dark and has no hierarchy. At this time, because the signal level detected by AGC is not low, the gain of the amplifier is very low, and the brightness of the main body of the picture cannot be improved. When backlight compensation is introduced, the camera only detects a sub-area of the whole field of view, and the working point of AGC circuit is determined by finding the average signal level of this area. Because the average level of the sub-region is very low, the AGC amplifier will have a higher gain, which will increase the amplitude of the output signal, thus making the main picture on the monitor clear, greatly reducing the subjective brightness difference between the background picture and the main picture, and improving the visibility of the whole field of view. Although backlight compensation improves the brightness of the subject, the image quality will be worse to some extent.

Wide dynamic technology is to expose twice at the same time, once fast and once slow, and then synthesize, which makes it possible to see bright and dark objects on the screen at the same time. Although both of them are measures to overcome the strong backlight environment and see the target clearly, backlight compensation is at the expense of the contrast of the picture, so in a sense, wide dynamic technology is an upgrade of backlight compensation.

Samsung TECHWIN (Sanxingguang Electronics) has rich experience in the national military industry due to its corporate background, and its products are more focused on industrial supplies, durability and stability. And has accumulated many years of experience in optics and semiconductor technology. It has a good performance in products using professional semiconductor chips such as security surveillance cameras and embedded hard disk video recorders. The third generation super-image technology SV Ⅲ (Figure 5) independently developed by SV Ⅲ is equipped with a two-speed scanning CCD, which can capture images with wide dynamic effects. And using two 12 digital input terminals, SV ⅲ has a wide dynamic range of more than 80db. After a large amount of digital information is transmitted to DSP through 23-bit data bus, DSP processes it internally to ensure that there is no data loss. Then the wide dynamic range is compressed into 10 bits by nonlinear adaptive WDR compression algorithm.

Using adaptive anti-mosaic color restoration algorithm, the color reaches 540 lines and 570 lines in black and white.

Powerful sensitivity enhancement technology provides dynamic 3D filtered images and optimizes the signal-to-noise ratio. And the visibility is enhanced under the condition of low illumination, and sufficient real-time effect is maintained.

Using advanced local contrast enhancement technology, ideal contrast can be obtained even in poor lighting conditions.

The unique color control algorithm can expand the application range of white balance, that is, it can accurately and truly reproduce colors in a wide range of color temperatures. This also means that it can well support the use of color mode and white balance in very low lighting conditions.

Typical application

At present, the focus of the low illumination wide dynamic camera used in road monitoring is the highway toll monitoring system, which mainly observes and records the toll situation of toll lanes, toll squares and toll stations, and implements effective supervision through the types of vehicles in toll lanes, the operation process of toll collectors, and emergencies and special events in the toll collection process. . Especially at night, toll booth staff need to see the license plate clearly. Generally speaking, after the light is turned on, the ambient illumination of the road surface and the illumination of the license plate form a certain dynamic range, so it is difficult for the traditional camera to "see clearly", so there is a demand for a low illumination and wide dynamic camera.

Secondly, the electronic police system, through closed-circuit television monitoring and automatic red light recording, improves the command center's intuition, real-time mobilization ability and response ability to traffic accidents, enhances the objectivity of investigating and handling violations, comprehensively coordinates and controls the controlled areas, and improves the traffic capacity of vehicles. Because we need to see the license plate clearly and monitor it 24 hours a day, there is a demand for a dynamic camera with low illumination and wide width.

In addition, there are some applications in urban commercial streets, which are used to grasp the traffic situation at some busy intersections, the running situation of vehicles around the road sections, the flow of pedestrians and traffic safety.

Concluding remarks

With the increasing awareness of traffic safety, road infrastructure must cooperate with the construction of road monitoring system, which undoubtedly indicates that the traffic monitoring industry contains huge business opportunities. And the camera with low illumination and wide dynamic is bound to have a broad space. As the winner of technology and digital world, Samsung TECHWIN is willing to contribute its strength to the intelligent transportation industry in China with high-quality products and first-class services.

Some broad dynamic technical knowledge

Wide dynamic range is the ratio of the brightest brightness signal value that an image can distinguish to the darkest brightness signal value that can be distinguished.

The expression of wide dynamics is expressed by "multiple" or "dB". When 100IRE is taken as the standard, the conversion formula is: N dB=20log(V2/V 1). The wide dynamic value of an ordinary camera (called V 1) is 10dB, for example, 48 dB, and the difference between it and the ordinary camera is 38 dB, V2/V 1=80, which shows that the wide dynamic difference between it and the ordinary camera is 80 times, and that of Panasonic's third-generation wide dynamic camera is 54 dB, V2/V/kloc. The typical dynamic range of ISD-A/KOOC-0/0 camera on the pool is 95 dB, v2/V/KOOC-0/=/KOOC-0/7782 times, and the maximum wide dynamic range is/KOOC-0/20 dB, v2/V/KOOC-0/= 3/KOOC-0/60. From the "multi" point of view, the wide dynamic range of the camera using Pixim DPS technology is greatly improved than that of CCD.