Main Functionality of CCD Camera

(1) Camera Format

Camera format is a measure of the size of the imaging area . It refers to the diagonal size of the imaging area.

Common optical formats include 1” , 2/3”, 1/2”, 1/3”, 1/4” and 1/5”. The respective diagonal length are as follows:

1 “ - Width 12. 8 mm , Height 9.6mm , Diagonal length 16mm .
2/3” - Width 8.8mm , Height 6.6mm , Diagonal length 11mm .
1/2” - Width 6.4mm , Height 4.8mm , Diagonal length 8mm .
1/3” - Width 4.8mm , Height 3.6mm , Diagonal length 6mm .
1/4” - Width 3.2mm , Height 2.4mm , Diagonal length 4mm .

Generally speaking, a larger CCD chip will have bigger area and therefore bigger area for taking light, thus increasing the sensitivity. In dim light condition, this will improve the picture quality and make the picture looks more natural.

(2) CCD Pixels

Images are made up of millions of picture elements called pixels . Active picture elements are the actual number of light-sensitive elements within the camera imaging device. Active picture elements are expressed with a vertical and horizontal number. A camera specified with 768H by 494V has 768 rows of horizontal elements and 494 rows of vertical picture elements.

The quality of a digital image, referred to as resolution, depends on the number of pixels used to create the image. The more the pixels are, the higher the resolution of the resulting image

(3) Horizontal Resolution

 Resolution is the ability of a camera to represent fine detail. The better theresolution, the more detail is perceivable to the observer. TV images are two dimensional, vertical and horizontal. Vertical resolution is measured by the number of alternate black and whitehorizontal lines that can be distinguished in the height of the camera image.

Horizontal resolution is measured by the number of alternate black and white vertical lines that can be distinguished in the width of thecamera image, multiplied by a correction factor (K factor) of 0.75 times to correct for the difference in the picture height to width ratio (3:4).

Vertical resolution is independent of system bandwidth it is often fixed for a given video standard (e.g. PAL or EIA). However, horizontal resolution remains variable and very much depends on to the quality of the transmission media (cables, etc.) and system bandwidth.

When "resolution" is discussed for camera comparison purposes it is generally presumed to be horizontal resolution.Horizontal resolution lies in the range from 320 to 500, expressed in TV Lines

4 ) Minimum Illumination

Minimum illumination is expressed in Lux. It is called sensitivity and refers to the minimum amount of light that will produce pictures.The lowerthe number, the more sensitive the camera is.

A camera requires 1.5 lux in order to capture a clear image. 0.1lux is equivalent to moonlight while 400 lux is equivalent to office lighting or a clear sunrise. The following are some typical light levels:

100000 Lux Sunny day
10000-100000 Lux Sunny day with some clouds
100-10000 Lux Overcast sky
100-1000 Lux Home/Office lighting
1-10 Lux Street lighting
0.1 Lux Full moon
0.01 Lux Young or Half moon
0.001 Lux Clear moonless night (starlight)
0.0001 Lux Dark cloudy moonless night (starlight)

CCD is categorized as

Standard Class. Minimum resolution is 1-3Lux.

Moonlight Class. Minimum resolution is 0.1Lux.

Starlight Class Miniimum resolution is 0.0005-0.001Lux

Infrared LED Class. Minimum resolution is 0Lux with the use of IR LED

Standard Camera	Starlight Class Camera

(5) Scanning System

Scanning system is categorized as PAL AND NTSC. PAL system (CCIR for B/W is adopted in China with 625 lines, 50 fields. NTSCsystem (EIA for B/W is adopted in Japan with 525 lines and 60 fields .)

(6) Power Supply

220V, 110 V and 24V is available for AC and 12V and 9V is available for DC supply.

(7) Signal to Noise (S/N) Ratio

Typical value for S/N ratio is 46dB. If the S/N ratio is over 50dB at zero AGC, this will give very accurate reproduction of the colors. Even when the AGC is automatically activated, the pictures remain sharp. there will be slight noise but the image quality is acceptable. If theS/N ratio is over 60dB, the image quality will be very good with very little noise.

( ８ ) Frames Per Second (FPS)

Frame rate, or frame frequency, is the measurement of the frequency (rate) at which an imaging device produces unique consecutive images called frames. Frame rate is most often expressed in frames per second (fps).

General speaking, FPS greater than 16 will be considered to be coherent. The higher the frame rate, the higher the degree of fluency screen. Universal video card can also reach 16-24 FPS. But for the highly-dynamic cameras, such as high-speed dome camera, the frame-rate which less than 24 per second, the screen will appear inconsistent, it is because the two are caused by different imaging principle.

Different demonstration of FPS