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1. What is a camera?
A camera is an electronic device that captures images and converts them into electrical signals. It typically uses a semiconductor imaging sensor, such as a CCD or CMOS chip, which allows it to offer advantages like high sensitivity, resistance to glare, minimal distortion, compact size, long lifespan, and good shock resistance. These features make cameras ideal for a wide range of applications, from everyday use to specialized surveillance systems.
2. How the camera works
When a camera captures an image, the lens focuses the light from the subject onto the image sensor. Each pixel on the sensor accumulates an electric charge proportional to the intensity of the light it receives. Under the control of video timing signals, this charge is then transferred pixel by pixel. The signal is then filtered, amplified, and processed to generate a video output. This video signal can be connected to a monitor or television, allowing users to view the captured image in real time.
3. Selection of resolution
Resolution is a key factor in determining image quality. It is measured in line pairs per millimeter (lp/mm) and refers to the number of alternating black and white lines that can be distinguished in the image. Black and white cameras typically have a resolution between 380 and 600 lines, while color cameras usually range from 380 to 480 lines. Higher resolution means sharper and more detailed images. For general surveillance, a 400-line black and white camera is often sufficient. However, for specialized applications such as medical imaging or forensic analysis, a 600-line camera may be necessary to achieve clearer results.
4. Imaging Sensitivity
Sensitivity refers to how well a camera performs in low-light conditions. It is usually expressed in lux, which measures the amount of light required for proper exposure. A black and white camera typically has a sensitivity range of 0.02 to 0.5 lux, while color cameras require more light, usually above 1 lux. Cameras with a sensitivity of 0.1 lux are suitable for standard surveillance, while those with 0.02 lux are better for nighttime or dimly lit environments. When using near-infrared lighting, low-light cameras are essential. Additionally, the sensitivity of a camera is also affected by the lens. For example, a lens with an f/0.75 aperture is equivalent to an f/1.2 lens at 2.5 lux, and an f/1.0 lens at 3.4 lux.
5. Electronic shutter
The electronic shutter controls how long the sensor is exposed to light. Its speed ranges from 1/50 to 1/100,000 seconds. Most cameras operate in automatic mode, adjusting the shutter speed based on ambient lighting to ensure clear images. Some models allow manual adjustment for specific applications where precise control is needed.
6. External Synchronization and External Trigger
External synchronization ensures that multiple video devices operate in sync, so their video signals align in terms of frame and line timing. This is achieved by inputting a composite sync (C-sync) or composite video signal into the camera. However, external synchronization does not guarantee a continuous frame of video from a specific moment. For such cases, cameras with external triggering capabilities are required.
7. Spectral response characteristics
Camera sensors are made of silicon, which is sensitive to near-infrared light, extending the spectral response up to about 1.0 micrometers. The peak sensitivity occurs at green wavelengths (around 550 nm). In low-light or nighttime surveillance, near-infrared illumination can be used, allowing the camera to capture images even when the human eye cannot see. The sensor also includes a UV-absorbing layer, making it insensitive to ultraviolet light. Color cameras, which use red, green, and blue filters, are generally less sensitive to infrared and ultraviolet light.
8. Chip size
The size of the image sensor plays a role in both the camera's physical dimensions and the field of view. Common sizes include 1/2", 1/3", and 1/4". Smaller sensors allow for more compact designs, but they also result in a narrower angle of view. Larger sensors provide a wider field of view when paired with the same lens. For example, a 1/2" sensor measures approximately 6.4mm x 4.8mm, while a 1/3" sensor is around 4.8mm x 3.6mm.
The camera system is typically installed on-site and consists of several components, including the camera body, lens, protective housing, mounting bracket, and pan-tilt head. Its main function is to capture the area under surveillance and convert the visual information into electrical signals. Cameras come in two main types: color and black and white. Black and white cameras generally offer higher sensitivity, making them more suitable for low-light environments. If the goal is to monitor movement or location, a black and white camera is often preferred. However, if identifying colors, such as clothing or surroundings, is important, a color camera is more appropriate.
Camera specifications vary in terms of sensor size, with common options being 1/3 inch, 1/2 inch, and 2/3 inch. Installation methods also differ, with fixed mounts and pan-tilt units available depending on the application requirements.