CCTV Video Surveillance System Design Questions and Answers — Questions and Answers
Question 1: A system designer needs to select a camera to provide evidential-quality video to identify a person's face at a distance of 10 meters. According to the DORI standard (IEC EN 62676-4), what is the minimum required pixel density for the 'Identification' level?
- 62 Pixels per Meter (PPM)
- 125 Pixels per Meter (PPM)
- 250 Pixels per Meter (PPM) (Correct answer)
- 25 Pixels per Meter (PPM)
Correct answer: 250 Pixels per Meter (PPM)
The DORI standard specifies different pixel densities for varying levels of detail. For 'Identification,' which enables the identity of an individual beyond a reasonable doubt, the standard requires a minimum of 250 Pixels per Meter (PPM).
Question 2: A client wants to install a camera pointed towards a building entrance that has a glass door, leading to strong sunlight during the day. This lighting condition causes individuals entering the building to appear as dark silhouettes. Which camera feature is specifically designed to correct this issue by balancing the light for the entire scene?
- Backlight Compensation (BLC)
- Wide Dynamic Range (WDR) (Correct answer)
- Highlight Compensation (HLC)
- Digital Noise Reduction (DNR)
Correct answer: Wide Dynamic Range (WDR)
Wide Dynamic Range (WDR) technology is designed to handle scenes with a high contrast between bright and dark areas, such as a bright background and a dark foreground. It captures multiple exposures of the scene and combines them to create a single image where details in both the bright and dark areas are visible. BLC brightens the entire image, which can wash out the already bright background, while HLC is for suppressing bright sources like headlights.
Question 3: When specifying a camera for a dimly lit warehouse that operates at night, which camera specification is most critical for determining its ability to produce a clear image in low-light conditions without relying on infrared illuminators?
- Focal Length
- IP Rating
- Lux Rating (Correct answer)
- Frame Rate (FPS)
Correct answer: Lux Rating
The Lux rating of a camera indicates the minimum amount of ambient light required to produce a usable image. A lower lux rating means the camera is more sensitive to light and can perform better in darker environments.
Question 4: You are designing a video surveillance system for a small retail store with 8 cameras, each recording 1080p video (approximately 4 Mbps bitrate) continuously. The client requires a video retention period of 30 days. Which of the following is the closest estimate for the total required storage capacity?
- 2 Terabytes
- 4 Terabytes
- 10 Terabytes (Correct answer)
- 20 Terabytes
Correct answer: 10 Terabytes
To calculate the storage: (4 Mbps per camera * 8 cameras) = 32 Mbps total bitrate. Convert Mbps to GB per day: (32 Mbps / 8 bits/byte * 3600 seconds/hour * 24 hours/day) / 1000^3 bytes/GB ≈ 345.6 GB/day. For 30 days: 345.6 GB/day * 30 days ≈ 10,368 GB, which is approximately 10.4 TB. Therefore, 10 Terabytes is the closest and most appropriate estimate among the choices.
Question 5: A designer is selecting a lens and camera combination to monitor a specific doorway that is 20 meters away. To ensure the doorway fills a significant portion of the camera's view, which two factors are most important to use in a Field of View (FoV) calculation?
- Camera Resolution and Frame Rate
- Lens Focal Length and Sensor Size (Correct answer)
- IP Rating and Lux Rating
- Video Compression and Bitrate
Correct answer: Lens Focal Length and Sensor Size
The Field of View (FoV) is determined by the camera's sensor size and the focal length of the lens. A longer focal length will produce a narrower field of view, making distant objects appear larger, while the sensor size defines the overall area that can be captured. These two parameters are essential for calculating the viewing angle and ensuring the target is framed correctly.
Question 6: Which of the following factors has the most significant impact on the network bandwidth required for an IP camera stream?
- Camera's physical dimensions
- Type of camera mount used
- Time of day
- Resolution and frame rate (Correct answer)
Correct answer: Resolution and frame rate
The resolution (e.g., 1080p, 4K) and frame rate (frames per second, FPS) are primary determinants of the amount of data generated by a camera. Higher resolution and higher frame rates create larger video files, which in turn require more network bandwidth to transmit the video stream effectively.
CCTV Video Surveillance System Design Questions and Answers
A system designer needs to select a camera to provide evidential-quality video to identify a person's face at a distance of 10 meters.
According to the DORI standard (IEC EN 62676-4), what is the minimum required pixel density for the 'Identification' level?