Monitoring camera electronic shutter application status and technical analysis

Tag: surveillance camera automatic aperture

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For an interlaced system, each complete picture is composed of two pictures of an odd field and an even field, that is, a total of 25 odd fields and 25 even fields per second, that is, 50 pairs. In the picture, the charge is accumulated on each CCD. If the transfer process of several fields of charge can be paused, the charge inside the photosensitive element can be temporarily stored until the charge is transferred to the scene for multiple times. The accumulation of charge to a larger number will undoubtedly increase the intensity of the signal and thus increase the brightness of the picture, but the consequence of this is to reduce the frame rate of the camera and cause frame loss. Therefore, the market is accumulating charges in this multi-field accumulation. Illumination cameras are usually only suitable for monitoring still scenes or non-sports scenes, so that even if you drop frames, you can't see them.

High speed electronic shutter

The high-speed electronic shutter allows the camera to clearly capture high-speed moving objects. Ordinary cameras can cause tailing when shooting high-speed or fast moving objects. This is because the electronic shutter speed of ordinary cameras is not fast enough, that is, the CCD sensing time is too long in one cycle, and the charge is accumulated on the CCD under the control of DSP. During this time, the different photosensitive positions of the object on the CCD have become like images, so the picture we see is an object with blur and tailing. How to avoid the tailing phenomenon? After understanding the cause of the tailing, we are very clear, as long as the camera's electronic shutter speed is fast enough, so that the CCD's sensing time is in each cycle (note that the cycle is not Change, still 1/50 second), the object will only be sensitive at one position of the CCD, then the image of this frame will be imaged in one position, if the actual photographic time of the CCD in each imaging cycle It is so short, then the motion of the object is clear on the continuous picture of the output. In general, as long as the frame rate per second reaches 15 or more, the image feels continuous, and the frame rate of the general PAL system is 25, so the continuity of the image can be guaranteed. In connection with real life, we can often see pictures of bullets or missiles flying on TV. These pictures are shot with high-speed cameras. The bullet's flight path is quite clear, and the camera's high-speed shutter plays an important role.

Fill light assist

The speed of the electronic shutter speed is accelerated, which causes the photographic time of the CCD to be greatly shortened. The consequence is that the charge accumulation is seriously insufficient, causing the picture to become dark. This is almost an irreconcilable contradiction. If it is to be solved, only the method of filling light can be adopted. The principle of the mouth is like this.

The camera used in the traffic bayonet has a high-speed electronic shutter function. This function ensures that when shooting a high-speed vehicle, since the electronic shutter speed is fast enough, the vehicle is only imaged at one position of the CCD every time, so the vehicle's motion track is clear. However, it is relatively dim. At the same time, when the electromagnetic coil of the local area feels that the vehicle is overspeed, the signal is fed back to the fill light, and the fill light is instantly lit. The CCD receives a large amount of object reflection during the allowed light-sensing time. The number of charges increases rapidly, so the license plate is clearly visible in the frame where the fill light is lit. This is why we can often see some lights blinking at the intersection. Of course, when the fill light flashes, it can be completely The software control of the control terminal can also fill light when the vehicle is not overspeed, and take bright and clear photos of the vehicle when needed.

Therefore, when shooting high-speed or fast-moving objects, it is generally preferred to use a high-speed electronic shutter camera that clearly shows the motion of the object, which is very suitable for shooting people or running pictures of the vehicle.

Auto iris effect

The automatic electronic shutter can also achieve the effect of automatic aperture. If the aperture is relatively small, the automatic electronic shutter will automatically adjust to the slow state, increasing the CCD sensing time to increase the brightness of the picture, but inevitably causing image smear. Correspondingly, if the aperture is too large, the amount of incoming light is too much, and the picture is very bright, then the automatic electronic shutter will automatically adjust to the fast state, reduce the actual sensitization time of the CCD, reduce the amount of charge accumulation on the CCD, and balance the picture. brightness.

Wide dynamic camera

At present, mature wide dynamic cameras on the market usually use CCD to image twice or multiple times. In the case of strong contrast between light and dark, the camera first exposes the scene with normal shutter speed. At this time, because the normal shutter speed is slow, the darker objects in the picture will be imaged normally, but because of the long sensing time, the bright objects in the scene will appear to be too bright, and then the camera will re-exposure with a faster shutter. At this time, the CCD sensing time is insufficient, and the imaging of bright objects is appropriate, but the darker objects in the original scene will be darker. The DSP function of the camera will combine the two sub-pictures to form a dark and dark scene. The brightness of each part of the object is more suitable for image output.

Since the wide dynamic camera inevitably uses the electronic shutter of normal speed, it will cause tailing when shooting fast objects. Therefore, it is not suitable for use as a traffic jam camera, and is only suitable for use in a cell door, etc. Occasionally, the speed of the vehicle is not fast, and because the contrast between the nighttime lights and the license plate is quite strong, this is precisely the suitable application for wide dynamic cameras.

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