Author: Han Yiyi Administrator Posted: 2011-03-29 22:14:47 Text: Large and Small Summary:
Camera Basics
1. What is a CCD camera? CCD is Charge Coupled Device (Charge Coupled Device) abbreviation, it is a semiconductor imaging device, and thus has a high sensitivity, glare resistance, small distortion, small size, long life, vibration and other advantages. 2. 2. CCD camera mode of operation The image of the subject through the lens focus to the CCD chip, the CCD according to the intensity of light accumulation of the corresponding proportion of the charge, each pixel accumulation of charge in the video under the control of the timing, point by point outward, after filtering, amplification, the formation of the video signal output. The video signal is connected to the video input of the monitor or television can see the same video image as the original image. 3. 3. Selection of resolution Evaluation of the camera resolution index is the horizontal resolution, its unit is the line, that is, after imaging the number of black and white line pairs can be resolved. Commonly used black and white camera resolution is generally 380-600, color 380-480, the larger the value of the clearer the imaging. General surveillance occasions, with about 400 lines of black and white cameras can meet the requirements. For medical, image processing and other special occasions, with 600 lines of the camera can get a clearer image. 4. 4. imaging sensitivity is usually the minimum ambient illumination requirements to show the camera sensitivity, black and white camera sensitivity is about 0.02-0.5Lux (Lux), color cameras more than 1Lux. 0.1Lux of the camera is used for ordinary surveillance occasions; in the night time or the environment of the use of light is weak, recommended the use of 0.02Lux of the camera. When used in conjunction with near-infrared lamps, it is also necessary to use a low-light camera. In addition, the sensitivity of the camera is also related to the lens, 0.97Lux/F0.75 is equivalent to 2.5Lux/F1.2 is equivalent to 3.4Lux/F1.
Reference ambient illuminance:
Summer sunshine 100000Lux Cloudy weather outdoor 10000Lux
Television studio 1000Lux Distance from the 60W table lamps 60cm desktop 300Lux
Indoor fluorescent lamp 100Lux Dusk indoor 10Lux
20cm candlelight 10-15Lux Night street light 0.1Lux 5. Electronic shutter The electronic shutter time is between 1/50-1/100,000 seconds, and the camera's electronic shutter is generally set to the automatic shutter mode, which can automatically adjust the shutter time according to the ambient light and darkness. The electronic shutter of the camera is usually set to automatic electronic shutter mode, which can automatically adjust the shutter time according to the brightness of the environment to get a clear image. Some cameras allow users to manually adjust the shutter time to adapt to certain special applications. 6. external synchronization and external trigger external synchronization refers to the same synchronization signal between different video devices to ensure synchronization of video signals, it can ensure that different devices output video signals have the same frame, line start and stop time. In order to achieve external synchronization, you need to give the camera input a composite synchronization signal (C-sync) or composite video signal. External synchronization does not guarantee that the user will get a complete and continuous frame from a specified moment, to achieve this function, you must use some special cameras with external trigger function. 7. Spectral Response Characteristics
CCD devices are made of silicon and are more sensitive to the near infrared, with a spectral response that extends to about 1.0um. The peak response is green light (550nm), and the distribution curve is shown on the right. Nighttime covert surveillance, you can use near-infrared light illumination, the human eye can not see the environment, but in the monitor can be clearly imaged. As the CCD sensor surface has a layer of ultraviolet-absorbing transparent electrodes, so the CCD is not sensitive to ultraviolet. Color camera imaging unit on the red, green, blue color filter strip, so the color camera is not sensitive to infrared, ultraviolet. 8. CCD chip size
CCD imaging size commonly used 1/2 "1/3", etc., the smaller the imaging size of the camera can be made smaller. In the same optical lens, the larger the imaging size, the larger the field of view. Chip specifications Imaging surface size (width X height) Diagonal 1/2 6.4x4.8mm 8mm 1/3 4.8x3.6mm 6mm
Camera Lens Selection Guide
In the TV monitoring system how to monitor the environment according to the scene, the correct choice of camera lenses is very important, because it has a direct impact on the composition of the system after the system at the end of the monitor to see the effects of the monitored surface painting. See the effect of the monitored surface painting can meet the design requirements of the system (in terms of the picture range or image details), so the correct choice of camera lens can make the system to optimize the design and can obtain good monitoring results. Camera lens on the aperture can be divided into manual aperture lens and automatic aperture lens two kinds of focal length can be divided into fixed-focus lens and zoom lens two kinds. The following is the use of different environments to talk about how to correctly select the camera lens. 1, manual, automatic aperture lens selection manual, automatic aperture lens selection depends on the use of environmental illumination is constant.
For a constant illumination in the environment, such as the elevator car, closed corridors, no direct sunlight in the room, can choose a manual aperture lens, so that the system can be installed in the initial debugging in accordance with the actual illumination of the environment, a one-time fixed lens aperture size, to obtain a satisfactory brightness of the screen can be.
For environmental illumination in the case of frequent changes, such as with the sunshine time and illumination changes in the foyer, windows and lobbies, etc., are required to choose the auto iris lens (must be equipped with an auto iris lens socket camera), so that you can realize the screen brightness automatically adjusted to obtain a good more constant brightness of the monitoring screen.
For the auto iris lens control signal can be divided into DC and VIDEO control of two kinds, namely, DC voltage control and video signal control. This is the type of auto iris lens selection, the camera auto iris lens socket connection, as well as the choice of auto iris lens drive mode switch, the three note that coordination can be good. 2, fixed-focus, zoom lens selection fixed-focus, zoom lens selection depends on the size of the scope of the monitored scene, as well as the requirements of the monitored scene picture clarity.
Lens specifications (lens specifications are generally divided into 1/3 ″, 1/2 ″ and 2/3 ″, etc.) a certain situation, the lens focal length and lens field of view angle of the relationship: the longer the focal length of the lens, the smaller the field of view angle of its lens (shown in Figure 1); in the case of a certain focal length of the lens, the lens specifications and the lens field of view angle of the relationship: the larger the lens specifications, the larger the field of view angle of its lens. So by the above relationship can be seen: in the case of a certain lens object distance, with the lens focal length of the larger, at the end of the system monitor to see the monitored scene of the screen range is smaller, but the details of the screen is increasingly clear; and with the lens specifications increase, at the end of the system monitor to see the monitored scene of the screen range increases, but the details of the screen is increasingly fuzzy. In the lens specifications and lens focal length under the premise of a certain, CS-type interface lens field of view will be greater than the C-type interface lens field of view.
The field of view of the lens can be divided into image horizontal field of view and image vertical field of view, and image horizontal field of view is greater than the image vertical field of view, usually we are talking about the field of view generally refers to the image of the lens horizontal field of view.
In the narrow environment to be monitored such as elevator cabin, small rooms should be used short focal length wide-angle or ultra-wide fixed focal length lens, such as the choice of lens specifications for 1/2″, CS-type interface, the lens focal length of 3.6mm or 2.6mm lens, these lenses are not less than 99 ° or 127 ° of the field of view of the lens, the camera for the camera in a small space in the general elevation of 2.5m or so, the lens field of view range is sufficient to cover the field of view of the lens. The field of view of the lens is sufficient to cover the entire close range of the narrow space being monitored. Can also be used according to the actual situation on the spot manual zoom lens such as Nissan Computar T2Z2814CS-2 lens, this lens for 1/3″ CS-type interface manual aperture lens, its focal length 2 times adjustable (manual focus). Focus range of 2.8 ~ 6.0mm, field of view angle change range of 96 ° ~ 47.2 °, this lens is very suitable for use in the narrow environment to be watched, in the use of convenient according to the actual needs of the flexible realization of the scene to be watched "point" or "surface
For the general zoom (times) lens, because of its minimum focal length is usually about 6.0mm, so its zoom (times) the maximum field of view of the lens is about 45 °, such as such a lens for the narrow environment to be watched, the monitoring of the dead zone is bound to increase, although it can be operated through the front end of the PTZ control to reduce the monitoring of the dead zone, but this will certainly increase the system's Engineering costs (the system needs to increase the front-end decoder, PTZ, shield, etc.), as well as the complexity of the system control, so in this environment, it is not appropriate to use the zoom (times) lens.
In the open monitored environment, first of all should be based on the degree of openness of the monitored environment, the user requirements at the end of the system monitor to see the clarity of the monitored scene picture, as well as being monitored by the center of the scene to the camera lens straight line distance between the reference basis, in the straight line distance to a certain extent and to meet the coverage of the entire monitored scene under the premise of the scene, you should try to consider the use of long focal lengths Lens, so that you can monitor the end of the system to get a clearer details of the monitored scene on the screen. In this environment can also consider the choice of zoom (times) lens (motorized three variable lens), which can be based on the system design requirements and the system's performance-price ratio decision, in the selection should also consider two points: (1) in the adjustment to the shortest focal length (look at the panoramic view) should be able to meet the requirements to cover the main scene being watched screen; (2) in the adjustment to the longest focal length (look at the details) should be able to meet the requirements of the observation of the scene being watched screen Detailed requirements. Under normal circumstances, in the indoor warehouse, workshop, factory and other environments generally choose 6 times or 10 times the lens can meet the requirements, and in the outdoor warehouse, dock, square, station and other environments, according to the actual requirements of the choice of 10 times, 16 times, or 20 times the lens can be (in general, the larger the lens multiplier, the higher the price, in the comprehensive consideration of the system cost under the premise of the appropriate choice of high multiples). Zoom lens). 3, the correct choice of lens focal length of the theoretical calculation of the lens field of view of the scene is an extremely important parameter, the lens field of view with the focal length of the lens and the size of the camera specifications and changes (the relationship between the changes as mentioned earlier), covering the scene of the focal length of the lens can be used to calculate the following formula:
(1) f = u-D/U
(2) f = h-D/H
f: lens focal length, U: the actual scene of the focal length, U: the actual scene of the focal length, U: the focal length, U: the actual scene of the focal length, U: the actual scene of the focal length, U: the focal length of the lens, f = h, f = h. Focal length, U: the actual height of the scene, H: the actual width of the scene, D: the measured distance from the lens to the scene, u: the height of the image, h: the width of the image For example:
When the 1/2″ lens is elected, the image size is u=4.8mm, h=6.4mm. the distance from the lens to the scene is D=3500mm, the actual height of the scene is U=2500mm (the actual width of the scene). can be calculated from the following formula H = 1.333-U, this relationship is determined by the camera viewfinder CCD slice).
Substitute the above parameters into the formula (1), can be obtained f = 4.8-3500/2500 = 6.72mm, so the choice of 6mm fixed-focus lens can be