CCD Camera Functions and Performance Indicators

CCD camera common functions and the major performance indicators include: the resolution, the lowest light, the signal-to-noise ratio, AGC, back light compensation, electronic shutter, White balance, and synchronous mode.

1.The resolution:

Resolution is an important parameter to evaluate cameras. It means that when a camera shoots the bars spaced at equal interval between black and white, the most number of lines could be seen on the screen of monitor (the resolution of the monitor ought to be higher than that of them). When the resolution is lower than this fixed line, a wilderness of gray shall appear on the screen.

The resolution of the camera used for industry is usually between 380~ 460 lines and that for broadcasting grade could reach around 700 lines. Resolution is subject to pixel of pick-up devices. It is obvious that the more the pixel of pick-up devices the image must be more legible and vice versa. The higher resolution, the higher class of the video camera or lower contrarily.

2.Minimum illumination

A unit measures the intensity of light. Full moonlight is about 0.1 lox whereas full daylight is about 10,000 lox. Most color cameras can produce decent images during deep twilight. Most black and white cameras need about as much light as produced by a full moon. With our new cameras, the only light you need is starlight on a dark night. This refers to the part of a video signal that carries the monochrome information.

3.S/N ratio

This is the ratio between the signal strength and the noise levels on an audio or video signal. It is the parameter for measuring quality of signals and sometimes used for expressing the sensitivity of an instrument, the higher the ratio is, the better the quality of the signal.

This is no simple task since numerous noise sources reside in a system—common ones include sensor noise, signal-conditioning electronic noise, analog-to-digital conversion uncertainty (modeled as noise), and software algorithm errors in extracting data from signals (modeled as noise).

4.Automatic Gain Control

This is a feature of many CCTV cameras that helps keep the strength of the output signal constant, even when the light level changes. For example, if the video signal is dark, it will attempt to increase the gain to bring the brightness up to a normal level. In other words, it boosts the signal strength at low light levels, and caps it at higher levels. Most cameras come with an AGC circuit. This circuit examines the brightness level of the video signal to keep it at a consistent level.

5.BackLight Compensation

The camera includes a BLC circuit. This circuit is used to help correct an image with more light behind the subject being viewed. Without backlight compensation, the subject appears dark with little detail. Using the backlight compensation will reduce the brightness of the light to allow the subject to appear brighter and bring out the details.

6.Electronic Shutter

Electronic Shutter, one of the major features of cameras, is not really a moving shutter, but a kind of signal processing. Under low light conditions, the CCD is allowed to gather signal at the electronic shutter speed of full 1/60th of a second. Under brighter lighting conditions, the video processing chip automatically responds by reading the CCD and then immediately "early purging" it, but each image is gathered over a much shorter period of time and the image is constantly monitored and optimized by advanced on board signal processing circuitry. The end result is a fantastic picture, with no fiddling, no adjustments, and best of all, unbelievable reliability.

7.White Balance

White Balance is used in Color cameras only. Different lighting sources provide different color temperatures. The white balance helps to correct these differences by adjusting the color processing to bring the color temperature to a fixed level. Without this balancing feature, due to the CCD’s poor adaptability, some colors would appear different (green instead of white in sunlight).It is divided into two kinds, one is AWB，Automatic White Balance, another is MWB, Manual White Balance.

AWB，Automatic White Balance is divided into Automatic Tracking White balance，ATW and Automatic White balance Control，AWC Automatic Tracking White balance is continuous adjustment with the change of color temperatures of objects，and the range is 2800~6000K。 Manual white balance is a setting that allows camera operators to match the exact lighting used. It is the professional way to shoot and is very easy to accomplish. The operator generally shoots a "white card" and presses a white balance button that adjusts the red, green and blue CCD signals so that the white card appears "white" and exhibits no color cast. This procedure, of course, must be performed every time you encounter different lighting conditions.

8.Sync system

Sync system has internal, Line-Lock and external sync. Devices with internal sync have an internal crystal to provide sync pulses without needing reference from any external device. The term Line-Lock refers to the 60 cycle AC (alternating current) supplied by the power company. This 60 cycle line frequency is the common reference used to lock the cameras together. For this reason only AC powered camera's have the Line-Lock feature. DC powered camera's are not capable of being Line-Locked. An external sync allows a piece of equipment to take its video synchronization from another unit, so that it can align itself with the system as a whole.