Glossary of car rear view camera system


☆BLC  
According to special area of measuring light and adjust the electrical shutter, the exposal value will be normal in the measuring area. 
 
☆Electronic Shutter  
Electronic Shutter, one of the major features of CCD camera, is not really a moving shutter, but a clever piece 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, resulting in precise control over the video level. Even at a shutter speed of 1/100,000th of a second, the CCD camera is still delivering 60 images per second, but each image is gathered over a much shorter period of time. The end result is a fantastic picture, with no fading, no adjustments, and best of all, unbelievable reliability. 
 
☆Gamma value  
It is a corrective value to take in account the fact that picture display re-produced by monitor is not linear. Generally it is set at 0.45; however with some industrial applications it is preferably set to 1. By changing gamma value the contrast of image is also changed. 
 
☆AC Adapter 
Alternating Current Adapter; when plugged to AC Power (usually 117V AC/60Hz in the United States) it produces 12V DC, 24V AC or others. "UL Listed" and "Regulated" recommended. It is also called Power Transformer.


12V DC
Most board cameras, mini cameras and about one third of the professional cameras work with 12V DC 100mA to 200mA for B/W cameras and 150mA to 300mA for color ones.


24V AC
About two thirds of the professional cameras work with 24V AC, 20V AC to 40V AC. The cameras usually have screw type connections and you don't need to worry about the polarity. This power is usually supplied with AC Adapter and you need to prepare separate power cable for the connection. Unlike 12VDC, this power can be transmitted to a long distance up to 450ft and is proper for the cameras that are to be installed out-door or when you don't have the power outlet near the camera. 
 
☆F/f  
Focal Length=(Distance to subject / Width of subject) x 4.5mm
 
For example, if you want to watch a subject of 5.5ft width at 10ft distance with a 1/3" CCD camera, you will need a 8.0mm FL lens. That is, 10ft / 5.5ft x 4.5mm = 8.18mm . A 8.0mm FL lens mounted on 1/3" CCD camera will cover the subject you want to watch.
Optical or lens speed. Smaller f-number means faster lens.
Optical Speed is about how fast a lens collects lights and is defined by the f-number like f/1.2, f/2.0, etc. This speed is determined by the Focal Length (FL) and the Diameter (D) of a lens; f-number = FL/D.
In conclusion, the lower the f-number, the more lights reaching the camera sensor and the better the video picture. The f-numbers are usually marked at the iris rings of lenses. 
 
☆Resolution 
Expressed by TV lines or pixels, it indicates the quality level of video images.

The industry of CCD video camera sensor uses pixels (picture elements) as its quality parameter. Medium resolution of B/W camera in EIA system is 510 horizontal pixels by 492 vertical pixels and is equivalent to 380 TV lines. High resolution is 768(H) x 492(V) pixels and equivalent to 570 TV lines. Color camera's medium resolution means 330TV lines and high resolution needs more than 460 TV lines.

The monitors in NTSC system have 525 vertical scanning lines regardless of their size. The horizontal 700 TV lines of B/W monitors represents medium level and more than 900 TV lines means high resolution in EIA system. The color monitor's horizontal resolution of 300 TV lines means medium quality and that of more than 450 TV lines means high resolution. 
 
☆TV SYSTEM
  
1.CCIR/EIA is for B/W system  
(1)CCIR is made the technical recommendation for the European 625 line standard for video signals. 
(2)EIA is American standard for B/W camera system. 


2.PAL/NTSC is for color system.  
PAL is a color television system, which is used in Europe, Australia , parts of Africa and the Middle East . It has 625 horizontal scan lines and 25 frames per second. (Frame: A whole video image; is composed of two interlaced fields. A CCD chip produces 30 frames per second at NTSC system and 25 frames at PAL. ) 
NTSC formulates standards for American color television system. NTSC system has 525 horizontal scan lines and 30 frames per second. 
 
☆Camera Sensor 
Video image sensor
CCD or C-MOS chip


CCD (charge coupled device) consists of several hundred thousand individual picture elements (pixels) on a tiny 1/2", 1/3", or 1/4" chip. Each pixel responds to light falling on it by storing a tiny charge of electricity. The pixels are arranged on a precise grid, with vertical and horizontal transfer registers carrying the signals to the camera's video processing circuitry. This transfer of signals occurs sixty times per second. The 1/3" CCD chip is the most widely used sensor format these days; its size is 5.5mm (diagonal), 4.4mm (horizontal) and 3.3mm (vertical). The 1/4" sensor format, recently being used in color cameras, is 4mm (diagonal), 3.2mm (horizontal) and 2.4mm (vertical).


C-MOS (Complementary - Metal Oxide Semiconductor) chip, also a video image sensor, produces much lower quality picture than CCD chip 
 
☆S/N ratio signal/noise ratio  
It is a measure showing the amount of interference caused by noise. Its value is important especially at low light values. The higher its value, the better will be the picture quality at low light levels. 
 
☆AGC  
The video signal is amplified at low light levels by an automatic gain control circuit. Unfortunately noise is also amplified. In some cameras the gain level can be controlled manually. (MGC = manual gain control).