1. CCD size, ie the target of the camera. The original is 1/2 inch, now 1/3 inch has been popularized, 1/4 inch and 1/5 inch have also been commercialized.
2. The CCD pixel is the main performance indicator of the CCD, which determines the clarity of the displayed image. The higher the resolution, the better the performance of the image detail. The CCD is made up of an array of photosensitive elements. Each element is called a pixel. The more pixels, the clearer the image. Most of the market is currently demarcated by 250,000 and 380,000 pixels, and those over 380,000 pixels are high-definition cameras.
3. Horizontal resolution. The typical resolution of a color camera is between 320 and 500 television lines, with 330, 380, 420, 460, and 500 lines. The resolution is represented by TV lines (referred to as line TV LINES), and the resolution of the color camera is between 330 and 500 lines. The resolution is related to the CCD and the lens, and it is also directly related to the frequency bandwidth of the camera circuit channel. The usual rule is that the frequency bandwidth of 1 MHz is equivalent to the resolution of 80 lines. The wider the band, the clearer the image and the larger the line value.
4. Minimum illumination, also known as sensitivity. It is the degree of sensitivity of the CCD to ambient light, or the darkest light the CCD needs to image normally. The unit of illuminance is LUX. The smaller the value, the less light is needed and the more sensitive the camera is. Moonlight and Starlight cameras with high sensitivities can work in very dark conditions.
1~3lux is general illuminance Moonlight type: The illuminance required for normal operation is about 0.1 LUX Starlight type: The illuminance required for normal operation is 0.01 LUX or less The infrared type uses infrared lamp illumination, and can be imaged without light (black and white)
5. Scan system. There are PAL and NTSC points. China uses the interlaced scanning (PAL) format (CCIR in black and white) with a standard of 625 lines and 50 fields. Only non-standard systems are used in medical or other professional fields. In addition, the transcript is NTSC format, 525 lines, 60 fields (black and white EIA).
6. Camera power supply. AC 220V, 110V, 24V, DC 12V or 9V.
7. Signal to noise ratio. The typical value is 46db. If it is 50db, the image has a little noise, but the image quality is good. If it is 60db, the image quality is good and no noise occurs.
8. Video output. Mostly 1Vp-p, 75Ω, using BNC connectors.
9. Lens mounting method. There are C and CS methods, the difference between the two is that the photosensitive distance is different.
10. Adjustable function of CCD color camera
(1) Selection of synchronization methods
A. For a single camera, the main synchronization methods are the following three:
Internal synchronization - Uses the crystal oscillator circuit inside the camera to generate the synchronization signal to complete the operation.
Out-of-sync - A synchronization signal generated by an external sync signal generator is sent to the external sync input of the camera for synchronization.
Power synchronization - also known as linear lock or line lock, uses the camera's AC power to complete the vertical push synchronization, ie camera and power supply neutral synchronization.
B. For multi-camera systems, it is desirable that all video input signals are vertically synchronized so that when converting the camera output, no picture distortion will result, but due to the power supply of each camera in the multi-camera system It may be taken from different phases in the three-phase power supply, or even the entire system is out of sync with the AC power supply. The measures that can be taken at this time are:
Both use the synchronization signal generated by the same external synchronization signal generator to feed the external synchronization input of each camera to adjust the synchronization.
Adjust the "phase adjustment" potentiometer of each camera. Because the vertical sync of the camera is in phase with the positive edge of the alternating current, the phase delay circuit can be used for each camera. Different phase shifts to achieve proper vertical synchronization with a phase adjustment range of 0-360 degrees.
(2) Automatic Gain Control All cameras have a video amplifier that amplifies the signal from the CCD to a level that can be used. The amplification, or gain, is equivalent to a high sensitivity, making it sensitive to low light. However, in a bright light environment, the amplifier will be overloaded, distorting the video signal. For this purpose, it is necessary to use a camera's automatic gain control (AGC) circuit to detect the level of the video signal and turn the AGC on and off in time to allow the camera to operate over a large range of illumination, ie, the dynamic range, ie, The sensitivity of the camera is automatically increased in low light conditions to increase the intensity of the image signal to obtain a clear image.
(3) Backlight Compensation Generally, the AGC working point of the camera is determined by averaging the entire field of view, but if the field of view contains a very bright background area and a very dark foreground target, then The AGC working point determined at this time may not be suitable for the foreground target, and the background light compensation may improve the foreground target display condition.
When the background light compensation is on, the camera only averages one sub-area of ​​the entire field of view to determine its AGC working point. If the foreground target is located in the sub-area, the visibility of the foreground target is expected to improve. .
(4) Electronic shutter
In the CCD camera, the shutter is operated with the charge accumulation time of the optically-controlled image surface. The electronic shutter controls the accumulation time of the camera CCD. When the electronic shutter is closed, the CCD accumulation time is 1/60 second for the NTSC camera and 1/50 second for the PAL camera. When the camera's electronic shutter is open, for the NTSC camera, its electronic shutter covers the range from 1/60 second to 1/10000 second with 261 steps; for the PAL type camera, the electronic shutter has 311 steps. Covers the range from 1/50 second to 1/10000 second. As the speed of the electronic shutter increases, the light focused on the CCD decreases during the time allowed by each video field, resulting in a lower camera sensitivity; however, a higher shutter speed creates a "pause" in viewing the moving image. The "action" effect, which will greatly increase the camera's dynamic resolution.
(5) White Balance
White balance is only used in color cameras. Its purpose is to realize the camera image can accurately reflect the scene conditions, there are manual white balance and automatic white balance in two ways.
A, automatic white balance Continuous mode - this time the white balance setting will be continuously adjusted with the change of the color temperature of the scene, the range is 2800~6000K. This method is most suitable for situations where the color temperature of the scene is constantly changing during shooting, so that the color is natural, but continuous white balance cannot produce the best color effect when there is little or no white in the scene.
Button mode - first aim the camera at a white target such as white wall, white paper, and then switch the automatic mode switch from manual to set position, keep it in this position for a few seconds or until the image appears white, in white balance After being executed, the automatic mode switch is switched back to the manual position to lock the white balance setting. At this time, the white balance setting will remain in the camera's memory until the execution is changed again. The range is from 2300 to 10000 K. During this period, this setting will not be lost even if the camera is powered off. Setting the white balance by buttons is the most accurate and reliable, suitable for most applications.
B. Manual White Balance Manual White Balance will turn off the automatic white balance. At this time, there are as many as 107 levels for changing the red or blue status of the image. For example, increase or decrease each level of red, increase or decrease each of blue grade. In addition to sub-times, some cameras have fixed the white balance at 3200K (incandescent level) and 5500K (dawn level) commands.
(6) Color adjustment For most applications, it is not necessary to make color adjustments on the camera. If adjustments are required, adjustments must be made so as not to affect other colors. The adjustable color modes are:
The red-yellow color increases, moving red to magenta one step.
The red-yellow color decreases, and the red color moves to yellow one step at a time.
Blue—The yellow color increases, moving the blue one step to the cyan.
Blue-yellow color decreases. Move blue to magenta one step at this time.
2. The CCD pixel is the main performance indicator of the CCD, which determines the clarity of the displayed image. The higher the resolution, the better the performance of the image detail. The CCD is made up of an array of photosensitive elements. Each element is called a pixel. The more pixels, the clearer the image. Most of the market is currently demarcated by 250,000 and 380,000 pixels, and those over 380,000 pixels are high-definition cameras.
3. Horizontal resolution. The typical resolution of a color camera is between 320 and 500 television lines, with 330, 380, 420, 460, and 500 lines. The resolution is represented by TV lines (referred to as line TV LINES), and the resolution of the color camera is between 330 and 500 lines. The resolution is related to the CCD and the lens, and it is also directly related to the frequency bandwidth of the camera circuit channel. The usual rule is that the frequency bandwidth of 1 MHz is equivalent to the resolution of 80 lines. The wider the band, the clearer the image and the larger the line value.
4. Minimum illumination, also known as sensitivity. It is the degree of sensitivity of the CCD to ambient light, or the darkest light the CCD needs to image normally. The unit of illuminance is LUX. The smaller the value, the less light is needed and the more sensitive the camera is. Moonlight and Starlight cameras with high sensitivities can work in very dark conditions.
1~3lux is general illuminance Moonlight type: The illuminance required for normal operation is about 0.1 LUX Starlight type: The illuminance required for normal operation is 0.01 LUX or less The infrared type uses infrared lamp illumination, and can be imaged without light (black and white)
5. Scan system. There are PAL and NTSC points. China uses the interlaced scanning (PAL) format (CCIR in black and white) with a standard of 625 lines and 50 fields. Only non-standard systems are used in medical or other professional fields. In addition, the transcript is NTSC format, 525 lines, 60 fields (black and white EIA).
6. Camera power supply. AC 220V, 110V, 24V, DC 12V or 9V.
7. Signal to noise ratio. The typical value is 46db. If it is 50db, the image has a little noise, but the image quality is good. If it is 60db, the image quality is good and no noise occurs.
8. Video output. Mostly 1Vp-p, 75Ω, using BNC connectors.
9. Lens mounting method. There are C and CS methods, the difference between the two is that the photosensitive distance is different.
10. Adjustable function of CCD color camera
(1) Selection of synchronization methods
A. For a single camera, the main synchronization methods are the following three:
Internal synchronization - Uses the crystal oscillator circuit inside the camera to generate the synchronization signal to complete the operation.
Out-of-sync - A synchronization signal generated by an external sync signal generator is sent to the external sync input of the camera for synchronization.
Power synchronization - also known as linear lock or line lock, uses the camera's AC power to complete the vertical push synchronization, ie camera and power supply neutral synchronization.
B. For multi-camera systems, it is desirable that all video input signals are vertically synchronized so that when converting the camera output, no picture distortion will result, but due to the power supply of each camera in the multi-camera system It may be taken from different phases in the three-phase power supply, or even the entire system is out of sync with the AC power supply. The measures that can be taken at this time are:
Both use the synchronization signal generated by the same external synchronization signal generator to feed the external synchronization input of each camera to adjust the synchronization.
Adjust the "phase adjustment" potentiometer of each camera. Because the vertical sync of the camera is in phase with the positive edge of the alternating current, the phase delay circuit can be used for each camera. Different phase shifts to achieve proper vertical synchronization with a phase adjustment range of 0-360 degrees.
(2) Automatic Gain Control All cameras have a video amplifier that amplifies the signal from the CCD to a level that can be used. The amplification, or gain, is equivalent to a high sensitivity, making it sensitive to low light. However, in a bright light environment, the amplifier will be overloaded, distorting the video signal. For this purpose, it is necessary to use a camera's automatic gain control (AGC) circuit to detect the level of the video signal and turn the AGC on and off in time to allow the camera to operate over a large range of illumination, ie, the dynamic range, ie, The sensitivity of the camera is automatically increased in low light conditions to increase the intensity of the image signal to obtain a clear image.
(3) Backlight Compensation Generally, the AGC working point of the camera is determined by averaging the entire field of view, but if the field of view contains a very bright background area and a very dark foreground target, then The AGC working point determined at this time may not be suitable for the foreground target, and the background light compensation may improve the foreground target display condition.
When the background light compensation is on, the camera only averages one sub-area of ​​the entire field of view to determine its AGC working point. If the foreground target is located in the sub-area, the visibility of the foreground target is expected to improve. .
(4) Electronic shutter
In the CCD camera, the shutter is operated with the charge accumulation time of the optically-controlled image surface. The electronic shutter controls the accumulation time of the camera CCD. When the electronic shutter is closed, the CCD accumulation time is 1/60 second for the NTSC camera and 1/50 second for the PAL camera. When the camera's electronic shutter is open, for the NTSC camera, its electronic shutter covers the range from 1/60 second to 1/10000 second with 261 steps; for the PAL type camera, the electronic shutter has 311 steps. Covers the range from 1/50 second to 1/10000 second. As the speed of the electronic shutter increases, the light focused on the CCD decreases during the time allowed by each video field, resulting in a lower camera sensitivity; however, a higher shutter speed creates a "pause" in viewing the moving image. The "action" effect, which will greatly increase the camera's dynamic resolution.
(5) White Balance
White balance is only used in color cameras. Its purpose is to realize the camera image can accurately reflect the scene conditions, there are manual white balance and automatic white balance in two ways.
A, automatic white balance Continuous mode - this time the white balance setting will be continuously adjusted with the change of the color temperature of the scene, the range is 2800~6000K. This method is most suitable for situations where the color temperature of the scene is constantly changing during shooting, so that the color is natural, but continuous white balance cannot produce the best color effect when there is little or no white in the scene.
Button mode - first aim the camera at a white target such as white wall, white paper, and then switch the automatic mode switch from manual to set position, keep it in this position for a few seconds or until the image appears white, in white balance After being executed, the automatic mode switch is switched back to the manual position to lock the white balance setting. At this time, the white balance setting will remain in the camera's memory until the execution is changed again. The range is from 2300 to 10000 K. During this period, this setting will not be lost even if the camera is powered off. Setting the white balance by buttons is the most accurate and reliable, suitable for most applications.
B. Manual White Balance Manual White Balance will turn off the automatic white balance. At this time, there are as many as 107 levels for changing the red or blue status of the image. For example, increase or decrease each level of red, increase or decrease each of blue grade. In addition to sub-times, some cameras have fixed the white balance at 3200K (incandescent level) and 5500K (dawn level) commands.
(6) Color adjustment For most applications, it is not necessary to make color adjustments on the camera. If adjustments are required, adjustments must be made so as not to affect other colors. The adjustable color modes are:
The red-yellow color increases, moving red to magenta one step.
The red-yellow color decreases, and the red color moves to yellow one step at a time.
Blue—The yellow color increases, moving the blue one step to the cyan.
Blue-yellow color decreases. Move blue to magenta one step at this time.