The main technical indicators of CCD color camera

The main technical indicators of CCD color camera 1 . CCD size, also known as color camera target. The original is 1/2 inch, now 1/3 inch has become popular, 1/4 inch and 1/5 inch have also been commercialized.

2. The CCD pixel, which is the main performance indicator of the CCD, 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 current market is delineated by 250,000 and 380,000 pixels, and those over 380,000 pixels are high-definition color cameras.

3. Horizontal resolution. The typical resolution of a color camera is between 320 and 500 TV 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. The minimum illuminance, 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. High-sensitivity cameras such as Moonlight and Starlight can work in very dark conditions.

1~3lux is general illuminance Moonlight type: The illumination required for normal work is about 0.1LUX. Starlight type: The illuminance required for normal operation is 0.01LUX. The infrared type uses infrared light to illuminate and can be imaged without light (black and white)

5. Scanning 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, Japan has NTSC format, 525 lines, and 60 fields (black and white EIA).

6. Color 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 method A. For a single surveillance camera, the main synchronization methods are as follows:

Internal synchronization - Use the crystal oscillator circuit inside the monitoring camera to generate the synchronization signal to complete the operation.

External Synchronization—Synchronization is accomplished by sending a synchronization signal generated by an external synchronization signal generator to the camera's external synchronization input.

Power synchronization - also known as linear lock or line lock, uses the AC power of the surveillance camera to complete the vertical push synchronization, which is the camera and power supply neutral synchronization.

B. For multi-monitoring camera systems, it is desirable that all video input signals are vertically synchronized so that when the camera output is transformed, no picture distortion color is caused, but the power supply of each camera in the multi-camera system may be taken from the three-phase power supply. The different phases in the system and even the entire system are out of sync with the AC power supply. The measures that can be taken at this time are:

All the synchronization signals generated by the same external synchronization signal generator are sent to the external synchronization input of each camera to adjust the synchronization.

Adjust the “phase adjustment” potentiometer of each camera. Since the vertical synchronization of the camera is in phase with the positive zero crossing of the rising edge of the AC, the phase delay circuit can make each camera have a different phase shift. Get the right vertical sync, phase adjustment range 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. Its amplification, which is the gain, is equivalent to a high sensitivity, making it sensitive to low light. In a bright light environment, the amplifier will be overloaded, distorting the video signal. For this purpose, the camera's automatic gain control (AGC) circuit is used to detect the level of the video signal and the AGC is switched on and off in time so that the camera can operate within a large range of illumination. This is the dynamic range, that is, when the illumination is low. The sensitivity of the camera is automatically increased to increase the intensity of the image signal to obtain a clear image.

(3) Background light compensation The camera's AGC working point is usually 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 work point may not be suitable for the foreground goal, 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 this sub-area, the visibility of the foreground target is expected to improve.

(4) Electronic shutter In the CCD camera, the shutter is operated by the charge accumulation time of the surface of the optically-controlled image. The electronic shutter controls the camera CCD accumulation time. 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 electronic shutter of the camera is turned on, for the NTSC camera, its electronic shutter covers the range from 1/60 second to 1/10000 second in 261 steps; for the PAL type camera, its electronic shutter covers 311 steps in 1/50 second. To 1/10000 second range. As the speed of the electronic shutter increases, the amount of light focused on the CCD decreases during the time allowed by each video field. As a result, the camera's sensitivity decreases. However, a higher shutter speed produces a "pause" for viewing the moving image. The 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 color temperature of the scene changes, the range of 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 a white wall, white paper, and then manually switch the automatic mode switch to the set position, hold it there for a few seconds or until the image appears white, and perform white balance After that, switch the automatic mode switch back to the manual position to lock the white balance setting. The white balance setting will remain in the camera's memory until it is changed again. The range is from 2300 to 10000 K. During this period, even Power loss to the camera will not lose this setting. 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 the times, some cameras have white commands that are fixed at 3200K (incandescent level) and 5500K (daylight level).

(6) Color adjustment For most applications, color cameras do not need to be color-adjusted, and adjustments need to be carefully adjusted to avoid affecting 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.

3. Digital adjustment control method The new camera adopts digital adjustment control to adjust the aforementioned optional parameters. At this time, it is not necessary to manually adjust the potentiometer but use the auxiliary control code. These adjustment parameters are stored in the digital memory unit. , increased stability and reliability.