CCD, is the English Charge Coupled Device that is the abbreviation of Charge Coupled Device, it is a special semiconductor device, there are many of the same light-sensitive elements, each light-sensitive element is called a pixel.CCD is an extremely important part of the camera, which plays a role in converting the light into electrical signals, similar to the human eye, so its performance will directly affect the camera's performance. The CCD is an extremely important part of the camera that converts light into electrical signals, similar to the human eye, so its performance will directly affect the performance of the camera.
Measuring the CCD good or bad indicators are many, there are the number of pixels, CCD size, sensitivity, signal-to-noise ratio, etc., of which the number of pixels as well as the size of the CCD is an important indicator. The number of pixels refers to the number of light-sensitive elements on the CCD. The image captured by a camera can be understood as consisting of many small dots, each of which is a pixel. Obviously, the more pixels, the clearer the picture will be, if the CCD does not have enough pixels, the clarity of the captured picture will be greatly affected, therefore, theoretically, the number of pixels of the CCD should be the more the better. However, the increase in the number of CCD pixels will make the manufacturing cost as well as the rate of finished products decreased, and in the current TV standards, the number of pixels increased to a certain number, and then increased to improve the clarity of the shooting screen becomes less obvious, therefore, the general number of pixels of about one million for general use has been sufficient.
Single CCD camera refers to the camera only a CCD and its brightness signal and color signal photoelectric conversion, which chromaticity signal is a CCD with some specific color masking device and combined with the back of the circuit is completed. As a CCD at the same time to complete the conversion of luminance signals and chrominance signals, so it is difficult to avoid both, so that the image captured in the color reproduction is not up to the professional level of the requirements. In order to solve this problem, there is a 3CCD camera. 3CCD, as the name suggests, is a camera using three CCDs. we know, if the light through a special prism, it will be divided into red, green, blue three colors, and these three colors is the three colors we use for television, through these three colors, you can produce all the TV signals, including the brightness signal. If a piece of CCD accepts each color separately and converts it to an electrical signal, and then processed by a circuit to produce an image signal, thus, it constitutes a 3CCD system.
Compared with a single CCD, 3CCD due to three CCDs were used to convert red, green, blue signals, captured images from the color reproduction than a single CCD to the natural, brightness and clarity than a single CCD is also better. But because of the use of three CCD, 3CCD camera price is much more expensive than a single CCD.
Digital camera specifications table in the CCD column is often written "1/2.7-inch CCD" and so on. Here "1/2.7 inch" is the size of the CCD, is actually the length of the CCD diagonal.
Existing digital cameras generally use 1/2.7-inch, 1/2.5-inch and 1/1.8-inch CCDs, etc. CCDs are a collection of light-receiving elements (pixels) that receive light through the lens and convert it into an electrical signal. With the same number of pixels, the larger the CCD size the larger the unit pixel. This allows more light to be collected per unit pixel, and can therefore theoretically be said to be conducive to higher picture quality.
But the image quality of a digital camera is not only determined by the CCD. The performance of the lens and the circuitry that creates the image from the electrical signals output by the CCD can also affect the image quality of the camera. It is incorrect to say that "large CCD = high image quality". For example, although 1/2.7-inch is smaller than 1/1.8-inch, digital cameras equipped with 1/2.7-inch CCDs have not been criticized for poor image quality.
Nowadays, pocket-sized digital cameras are getting smaller and lighter, and most of them use small 1/2.7-inch CCDs for design reasons.
By the way, the word "type" for 1/2.7-inch is sometimes written as "inch. ", however, in this case is not the ordinary "1 inch = 25.4mm". Because of the combination of CCD debut on the camera tube and display used in the former camera, so it is customary to use a more specific size. 1/2.7 inches is 6.6mm, 1/1.8 inches is about 9mm.
CCD camera selection and classification
CCD chip is like a human retina, is the core of the camera. At present, our country is not yet capable of manufacturing, most of the cameras on the market are used in Japan SONY, SHARP, Panasonic, LG and other companies to produce the chip, and now South Korea also has the ability to produce, but the quality is a little inferior. Because of the chip produced by different levels of production, each manufacturer to obtain different ways and other reasons, resulting in CCD acquisition effect is also very different. At the time of purchase, you can take the following methods of detection: turn on the power, connect the video cable to the monitor, close the lens aperture, see if the image is completely black when there are bright spots, the screen snowflake big or not, these are the detection of the CCD chip is the most simple and direct method, and does not require other specialized instruments. Then you can open the aperture, look at a still life, if it is a color camera, it is best to ingest a brightly colored object, to see whether the image on the monitor is off-color, distorted, color or gray scale is smooth. A good CCD can well restore the color of the scene, so that the object looks clear and natural; while the image of the defective product will have a color deviation phenomenon, even if the face of a piece of white paper, the image will show blue or red. Individual CCD due to the dust of the production plant, CCD target surface will have impurities, in general, the impurities will not affect the image, but in low light or microscopic camera, fine dust can also cause adverse consequences, if used for this type of work, be sure to carefully select.
1, according to the imaging color
Color camera: applicable to the scene of fine discrimination, such as identifying the color of clothing or scenery.
Black-and-white cameras: for poorly lit areas and areas where lighting cannot be installed at night, black-and-white cameras can be used to monitor only the location or movement of the scene.
2, according to the resolution of sensitivity and other divisions
Image pixels below 380,000 for the general type, especially 250,000 pixels (512 * 492), the resolution of 400 lines of the most common products.
High-resolution type with more than 380,000 pixels.
3, according to the CCD target size
CCD chip has been developed in a variety of sizes:
Currently used in most of the chip for 1/3 "and 1/4". In the purchase of the camera, especially on the camera angle has more stringent requirements, the size of the CCD target surface, CCD and lens with the situation will directly affect the size of the field of view and image clarity.
1 inch - target surface size of 12.7mm wide * 9.6mm high, 16mm diagonal.
2/3 inch - target surface size of 8.8mm wide * 6.6mm high, 11mm diagonal.
1/3 inch - target surface size of 8.8mm wide * 6.6mm high, 11mm diagonal.
1/2 inch - target surface size is 6.4mm wide * 4.8mm high, 8mm diagonal.
1/3 inch - target surface size is 4.8mm wide * 3.6mm high, 6mm diagonal.
1/4 inch - target surface size of 3.2mm wide * 2.4mm high, diagonal 4mm.
4, according to the scanning system
PAL system, NTSC system. China uses interlaced (PAL) system (black and white for the CCIR), the standard is 625 lines, 50 fields, only medical or other specialized areas to use some non-standard system. In Japan, the standard is NTSC, 525 lines and 60 fields (EIA in black and white).
5, according to the power supply
110VAC (NTSC is mostly such);
220VAC
24VAC
12VDC
9VDC (miniature cameras are mostly such).
6, according to the synchronization mode
Internal synchronization: the synchronization signal generated by the synchronization signal generation circuit within the camera to complete the operation.
External synchronization: using an external synchronization signal generator, the synchronization signal into the camera's external synchronization input.
Power Sync (Linear Lock, LINE LOCK): Vertical push synchronization is accomplished using the camera's AC power supply.
External VD Sync: Input the VD sync pulse from the camera signal cable to complete the external VD sync.
Multi-camera external synchronization: Fixed external synchronization of multiple cameras, so that each camera can operate under the same conditions, due to the synchronization of the cameras, so that even if one of the cameras converted to other scenes, synchronization of the camera's screen will not be distorted.
7, in accordance with the degree of division, CCD is divided into:
Ordinary type of illumination required for normal operation 1 ~ 3LUX
Moonlight type of illumination required for normal operation 0.1LUX or so
Starlight type of illumination required for normal operation 0.01LUX or less
Infrared type of illumination using infrared lamps, in the absence of light can be Imaging
CCD color camera main technical indicators
CCD size, that is, the camera target surface. Original more than 1/2 inch, now 1/3 inch has been popularized, 1/4 inch and 1/5 inch has also been commercialized.
CCD pixels, is the main performance indicator of the CCD, which determines the degree of clarity of the display image, the higher the resolution, the better the performance of the image details.CCD is composed of a surface array of light-sensitive elements, each element is called a pixel, the more pixels, the more clear the image. Nowadays, the market is mostly demarcated by 250,000 and 380,000 pixels, and those with more than 380,000 pixels are high-definition cameras.
Horizontal resolution. The typical resolution of color cameras is between 320 and 500 TV lines, mainly 330 lines, 380 lines, 420 lines, 460 lines, 500 lines and other different grades. Resolution is expressed in terms of television lines (referred to as lines TV LINES), the resolution of the color camera is between 330 and 500 lines. Resolution and CCD and lens-related, but also with the camera circuit channel bandwidth is directly related to the usual law is 1MHz bandwidth equivalent to the clarity of 80 lines. The wider the bandwidth, the clearer the image, the greater the relative value of the line.
Minimum illumination, also known as sensitivity. Is the degree of sensitivity of the CCD to ambient light, or the CCD normal imaging needs the darkest light. The unit of illumination is lux (LUX), and the smaller the value, the less light is needed and the more sensitive the camera is. Moonlight level and starlight level and other high sensitivity camera can work in very dark conditions, 2 ~ 3lux is a general illumination, now there are less than 1lux of the ordinary camera came out.
Scanning system. There are PAL and NTSC system.
Camera power supply. AC 220V, 110V, 24V, DC 12V or 9V.
Signal-to-noise ratio. Typical value of 46db, if 50db, the image has a small amount of noise, but the image quality is good; if 60db, the image quality is excellent, no noise.
Video output. Mostly 1Vp-p, 75Ω, all with BNC connectors.
Lens mounting method. There are C and CS way, the difference between the two is that the light-sensitive distance is different.
Adjustable Functions of CCD Color Camera
Selection of Synchronization Methods
A. For a single camera, the main synchronization methods are as follows:
Internal synchronization - the use of the camera's internal crystal oscillator circuit generates synchronization signals to complete the operation.
External synchronization - using an external synchronization signal generator to generate a synchronization signal sent to the camera's external synchronization input to achieve synchronization.
Power synchronization - also called linear lock or line lock, is the use of the camera's AC power supply to complete the vertical push synchronization, that is, the camera and power supply zero line synchronization.
B, for multi-camera system, hope that all the video input signals are vertically synchronized, so that when changing the output of the camera, will not cause distortion of the picture, but due to the multi-camera system of the camera power supply may be taken from the three-phase power supply of different phases, and even the whole system and AC power supply is not synchronized, at this time, can be taken to take measures are:
All using the same external Synchronization signal generated by the synchronization generator is fed into the camera's external synchronization input to adjust the synchronization.
Adjust the camera's "phase adjustment" potentiometer, because the camera in the factory, its vertical synchronization is the same phase with the rising edge of the AC positive zero point, so the use of phase delay circuit can make each camera has a different phase shift, so as to obtain the appropriate vertical synchronization, the phase adjustment range of 0 ~ 360 degrees.
Automatic gain control
All cameras have a signal from the CCD will be amplified to the level of video amplifier can be used to amplify a large number of that gain, which is equivalent to have a high sensitivity, which can be made in the low light sensitive, however, in the bright light environment amplifier will be overloaded, so that the video signal distortion. For this reason, the need to use the camera's automatic gain control (AGC) circuit to detect the level of the video signal, switch AGC at the right time, so that the camera can work in a larger range of light, which is the dynamic range, that is, in low light automatically increase the sensitivity of the camera, thereby increasing the intensity of the image signal to obtain a clear image.
Backlight compensation
Usually, the camera's AGC operating point is determined by averaging the contents of the entire field of view, but if the field of view contains a very bright background area and a very dark foreground target, the AGC operating point determined at this time may not be appropriate for the foreground target, the background light compensation may improve the foreground target display.
When the background light compensation is on, the camera averages only a sub-area of the entire field of view to determine its AGC operating point, and if the foreground target is located in this sub-area, the visibility of the foreground target is expected to improve.
Electronic shutter
In a CCD camera, the shutter is manipulated by optically electrically controlling the charge build-up time on the image surface. The electronic shutter controls the accumulation time of the camera's CCD, which is 1/60th of a second for NTSC cameras and 1/50th of a second for PAL cameras when the electronic shutter is closed. When the electronic shutter of the camera is open, for NTSC cameras, its electronic shutter covers the range from 1/60 second to 1/10,000 second in 261 steps; for PAL cameras, its electronic shutter covers the range from 1/50 second to 1/10,000 second in 311 steps. When the electronic shutter speed increases, in the time allowed for each video field, the light focused on the CCD is reduced, the result will be a reduction in the sensitivity of the camera, however, higher shutter speeds for the observation of moving images will produce a "stop-motion" effect, which will greatly increase the dynamic resolution of the camera.
White balance
White balance is used only for color cameras, its purpose is to achieve the camera image can accurately reflect the scene conditions, there are manual white balance and automatic white balance two ways.
A, automatic white balance
Continuous way - this time the white balance settings will be continuously adjusted with the scene color temperature changes, the range of 2800 ~ 6000 K. This way for the scene of the color temperature in the shooting during the occasions is the most appropriate, so that the color performance is natural, but for little or even in the scene of the color temperature is not changed during the occasion, so that the color performance is natural, but for the scene of the color temperature is not changed during the shooting. However, continuous white balance does not produce the best color results when there is little or no white in the scene.
The Push Button Method - Aim the camera at a white target, such as a white wall or white paper, and then flip the AUTO switch from the manual to the set position, hold it there for a few seconds or until the image appears white, and then flip the AUTO switch back to the manual position to lock in the white balance setting after the white balance has been performed. At this time, the white balance setting will remain in the camera's memory until the implementation of the change again, the range of 2300 ~ 10000K, during this period, even if the camera power failure will not be lost. Setting the white balance in the push-button mode is the most accurate and reliable, and is suitable for most applications.
B, manual white balance
Open manual white balance will turn off the automatic white balance, this time to change the image of the red or blue condition has up to 107 levels for adjustment, such as increasing or decreasing the red each a level, increase or decrease the blue each a level. In addition to this, some cameras have a white balance will be fixed at 3200K (incandescent level) and 5500K (daylight level) and other gear commands.
Color Adjustment
For most applications, there is no need for the camera color adjustment, such as the need to adjust the need to carefully adjust so as not to affect the other colors, adjustable color way:
Red - yellow color increase, this time the red to magenta move one step.
Red-yellow color decreases, then move the red to yellow one step.
The orchid-yellow color increases, at this point move the orchid color one step toward the cyan orchid color.
The orchid-yellow color decreases, at which point the orchid color is moved one step toward magenta.
CCD camera main technical parameters explained:
1. What is a CCD camera?
CCD is Charge Coupled Device (Charge Coupled Device) abbreviation, it is a semiconductor imaging device, and thus has the advantages of high sensitivity, resistance to strong light, distortion, small size, long life, anti-vibration and so on.
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 the light accumulates the corresponding proportion of the charge, each pixel accumulates charge in the video under the control of the timing, point by point outward, after filtering, amplification, the formation of video signal output. The video signal is connected to the video input of the monitor or TV set to see the same video image as the original image.
3. Selection of resolution
The evaluation of the camera resolution index is the horizontal resolution, its unit is the line pair, that is, the number of black and white line pairs that can be resolved after imaging. 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 camera can meet the requirements. For medical, image processing and other special occasions, with 600 lines of the camera can get a clearer image.
4. imaging sensitivity
Often use the minimum ambient illumination requirements to indicate the camera sensitivity, the sensitivity of the black and white camera is about 0.02-0.5Lux (Lux), the color camera is more than 1Lux. 0.1Lux of the camera is used for ordinary surveillance occasions; in the night time or the environment of the light is weaker, it is recommended to use a 0.02Lux camera. The 0.1Lux camera is used for ordinary surveillance occasions; when used at night or when the ambient light is weak, 0.02Lux is recommended. 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 to the ambient illuminance: summer sunshine 100000Lux cloudy weather outdoor 10000Lux TV studio 1000Lux 60cm desktop from 60W lamp 300Lux indoor fluorescent lamp 100Lux Dusk indoor 10Lux 20cm candlelight 10-15Lux Night street lamp 0.1Lux
5. Electronic shutter
Electronic shutter time between 1/50-1/100000 seconds, the camera's electronic shutter is generally set to automatic electronic shutter mode, according to the environment of the brightness of the shutter time automatically adjusted to get a clear image. Some cameras allow users to manually adjust the shutter time to adapt to some special applications.
6. External synchronization and external triggering
External synchronization refers to the same synchronization signal between different video devices to ensure that the video signal synchronization, which can ensure that the output of the video signal from different devices have the same frame, line start and stop time. In order to achieve external synchronization, it is necessary to input a composite synchronization signal (C-sync) or composite video signal to the camera. External synchronization does not guarantee that the user will get a complete and continuous frame from the specified moment, to achieve this function, you must use some special cameras with external triggering capabilities.
7. Spectral Response Characteristics
The CCD device is made of silicon and is 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" and so on, the smaller the size of 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 specification Imaging surface size (width X height) Diagonal 1/2 6.4x4.8mm 8mm 1/3 4.8x3.6mm 6mm