Using CCTV Chicago Public Video Surveillance Chicago Systems for Crime Control


CCTV Systems Chicago, IL

A. Video Quality
Video Quality is the video delivered to end users that allows them to recognize objects.
Other terms used to refer to video quality are “visual intelligibility” and “visual acuity.” These equate to
a visual extension of a “can you hear me” audio test, rephrased as “can you see me?” This guide reflects
this concept; as it allows a user to specify end-to-end system performance or individual component
performance. This guide is based on the following key concepts:
• Every application is trying to recognize a desired target to a particular level of discrimination.
• The ability to perform a specified task determines the required video quality being delivered.
B. Use Case
The first step to getting the appropriate video quality to match a user’s needs is to clearly define
functional requirements, or use case. At the most basic level, this depends on the answers to only two
1. What is in the scene of interest, or scene content?
2. What is the desired task to be accomplished from viewing that scene?
The answers to these two questions define the use case. All emergency response video systems must
present a scene of interest to a remote user in sufficient detail for the user to make a decision or
perform a task based on recognition of what is happening in the scene. For example, the end user must
be able to read the characters in a license plate or determine the identities of individuals at a local
convenience store while performing surveillance

Use Characteristics for CCTV Systems Chicago IL
1. Discrimination Level
Video may be used to identify a wide range of detail, from motion detection to positive identification of
a person for forensic evidence. Not every video system needs to perform positive identification. The
video system selected should conform to the application requirements, without over- or under-
specifying the system.
2. Usage Timeframe for CCTV Systems Chicago IL
To what level of discrimination does the user need to recognize the target?
If a user needs to determine only whether there are people present in a scene, “General Elements of the
Action” would suffice. If the user requires large-scale recognition, such as the distinction between a car

and a van, then “Target Class Recognition” fits the users’ system needs. A value of “Target
Characteristics” indicates the need to recognize gender and markings, and distinguish smaller actions,
and “Target Positive ID” indicates the most specific discrimination level.
Scene Content
3. Target Size for CCTV Systems Chicago IL
The size of the region of interest (target) with respect to the size of the field of view directly affects the
ability to recognize that target when the camera is at its maximum optical zoom. The larger the target,
relative to the field of view, the more details can be discerned. The perceived target size is dependent
on the actual target size, its distance from the camera, and the camera’s field of view. Figures 4 and 5
demonstrate the difference between a large target size and a small target size. PSCR is developing
measurements to more precisely define target size.

4. Motion in the scene (e.g., background, target or camera)
Motion can come from the target (e.g., a car driving by), the background (e.g., a large crowd), or from
the camera itself moving (e.g., a dash-mounted camera in a police car). Motion affects the length of
time a desired target is shown in the video frame, and can cause the target to blur. High motion can be
caused by either many moving objects within the scene (see Figure 6) or a single object moving quickly.

5. Lighting Level for CCTV Systems Chicago IL
Lighting levels can vary from very dark (e.g., nighttime or indoors) to very bright (e.g., daylight or
spotlight), affecting the ability of the camera to capture the image. The presence of both very bright
areas and very dark areas in the frame simultaneously is known as high dynamic range, and can impair
target recognition, as shown in Figure 7.

The combinations of the end user’s specific needs in these five areas comprise the Generalized Use
Class. There are many more aspects that affect video, and each of these parameters has an infinite
number of possible values. This document addresses the most important aspects and defines a
manageable number of choices for each. VQiPS WG made a concerted effort to provide a balance
between complexity and simplification. We specialize in CCTV Systems Chicago IL.


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