Cameras

Cameras

Copyright: © 2014 |Pages: 25
DOI: 10.4018/978-1-4666-4896-8.ch021
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Abstract

The very first element in the video surveillance system is the device that captures the images, which is the camera. This is a very important chapter in the book as it discusses the concepts of analog and digital cameras, its various designs, and camera specifications. Proper camera choice as well as setting is a very important issue in video surveillance system installation and design.
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1. Introduction

The notion camera stems from the Latin word camera which translates to room and when we go further into the origin of this word we come to the Latin expression “camera obscura”, which means “dark room.” “Camera obscura” was a lightproof room, of a box shape, where a convex lens was placed at one end and a screen that reflected the image at the other end of it. It assisted artists to produce paintings in the Middle Ages.

In the nineteenth century, “camera” referred to a device for recording images on film that consisted of a lightproof box, a lens through which light entered and was focused, a shutter that controlled the duration of the lens opening, and an iris that controlled the amount of light that passed through the glass.

The first negative film image was produced in 1826 by Joseph Nicéphore Niépce and it is considered to be the birth of photography.

The lens of a video camera first receives the light reflected from a focused scene and then concentrates it for the camera’s image sensor. The image sensor functions by converting the image from the lens into a time-varying electronic signal. This signal is processed by the camera’s electronics, and a transmitter (two-wire unshielded twisted-pair UTP, coaxial cable, fiber optics, or wireless) sends it to a monitor.

Figure 1 illustrates a simple system: camera, lens, and monitor.

Figure 1.

The simplest configuration: one video camera and one monitor

Cameras (monochrome/color, solid-state/thermal IR) scan the vertical and horizontal pixels picked up by the camera’s sensor.

These pixels are converted into a signal representative of the scene’s color and light information as a function of time. The scene can then be recorded or reconstructed on a remote monitor.

Video cameras collect information about a scene point-by-point until they have one frame that shows a complete scene. This process differs from human eyes, film cameras, and low light level light intensifiers, which see an entire scene all at once.

Video cameras function much like typewriters: the element moves from left to right until it reaches the right corner, then returns to the left and begins a new line. Most video cameras work this way, adding a second “carriage return” after each line until the end of the page or bottom of the screen. This is how they complete one field, or half of the video image (Kruegle, 2007).

Then the scanner moves back up to the second line (the first blank line on the screen) and fills in all the remaining blank lines, completing the second field or a full video frame. This repeats for each frame. This process is called interlaced scanning. Some cameras, and also computer monitors, utilize progressive scanning, which fills in one line after another without skipping any.

Again, the camera sensor converts either an IR light image or a visual image into an image that the camera’s scanner can read in a point-by-point or line-by-line fashion. It then creates a time-dependent electrical signal to represent the light intensity of the focused scene.

Color cameras require this process to be repeated three times in order to convert red, green, and blue inputs into an electrical signal.

Analog video cameras always include:

  • 1.

    An image censor.

  • 2.

    A synchronized electronic scanning system.

  • 3.

    Timing electronics.

  • 4.

    Electronics for amplifying and processing video.

  • 5.

    Electronics for synchronizing and combining video signals.

The electronics for synchronizing and combining create a complete video output signal.

Scanning must be fast (at least 30 fps) to record scenes with movement.

Synchronizing signals must be adequate in order to produce stable displays and recordings.

Digital video cameras contain:

  • 1.

    An image sensor.

  • 2.

    Circuitry for reading horizontal and vertical pixels.

  • 3.

    Digital signal processing DSP circuits.

  • 4.

    Electronics for synchronizing and combining video signals (for a complete video output signal).

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