The Minimum Illumination
The minimum illumination means a figure that the object brightness is as low as the regulated degree of a camera video signal output. Generally, the minimum illumination of a color camera is 2~~3LUX. An illumination testing should be with a premise of a lens aperture quotiety. With the same lens aperture quotiety, the minimum illumination lower the camera grade higher. Different from color cameras, the black and white cameras have no color-processing and just are sensitive to the brightness degree of light signal. So, the minimum illumination of black white camera is lower than that of color ones. The minimum illumination of black white camera can be 0.1LUX with F1.4, and the glimmer cameras can be lower. To the lens aperture quotiety, pls take a reference on the chapter of LENS.
The Nominal value of video signal is 1Vp-p and the standard one is 0.7Vp-p, whose minimum illumination is standard from 1/3 to 1/2. So the image under the minimum illumination can’t be as the day effect, and its clear degree is tested with TV signal test card, white and black strips alternate, requiring the black reflectivity near to 0% and the white reflectivity bigger than 89.9%. In locale, however, we can’t get the standard testing environment, for example, leaves and grasses have low reflectivity. When the contrast is low, it is not easy to get a clear image. So, it can’t use the minimum-illumination-measure of camera as the standard of locale illumination in a real use.
Camera signal-to-Noise Ratio
Signal-to-Noise Ratio is one index for measuring camera performance. For a bright scene, the monitor shows a clearer image, and it is not easily conscious of the hot interference. But for a light dark scene, the image on screen is caliginous and easily seen the snowflake. It has a direct relationship between the camera index of Signal-to-Noise ratio and the hot interference (The Hot Interference Impact on the image). It is to say that, it is high of the camera Signal-to-Noise when the impact on image is low.
The Signal-to-Noise Ratio is a ratio of signal voltage to noise one, notified by the mark S/N. Ordinarily, the signal voltage is far higher than the noise one. So we usually take the logarithm with 10 for admission from this ratio calculated with average values, and then multiply by coefficient 20, notified with the unit dB.
The Signal-to-Noise Ratio of camera is usual tested with turnoff AGC (Automatic Gain Control). When AGC turns on, it causes a higher noise level by raising the little signals. And, the CCD camera typical value of Signal-to-Noise Ratio is 45dB~55dB. To measure the Signal-to-Noise Ratio parameters, it should connect the video instrument for clutter-wave measuring directly onto the camera video fan-out
AGC——Automatic Gain Control. All cameras have the video magnifiers for an applied standard to blow up the CCD signals. The plus, enlarged value, is equal to a sensitivity effect. This video magnifier increases the camera sensitivity to catch images with weak light, but when light is strong, magnifier over-loading will make video signal aberrant. Thus, an Automatic Gain Control (AGC) can detect the video signal level. To get a clear image, timely turn on or off the AGC getting a larger illumination working range, namely dynamic rang, and raising automatically the camera sensitivity under the minimum illumination to enhance the image signal. The cameras with AGC function can strengthen its sensitivity under the minimum illumination, and the hot interference is delomorphic then, since the enlargement happens at the same time for both signal and noise.
ES---Electronic Shutter, an item compares to the camera machine shutter, like the sensitization time of controlling the CCD image sensor. Essentially CCD sensitization is to accrue signal charge. When time for sensitization is long, the signal charge is accrued much and the output signal currency amplitude is bigger. It can realize controlling the CCD sensitization time by adjusting the signal charge accruing time (adjusting the width of timepiece pulse).
WB--- White Balance, only for color camera, realizes that the camera image can reflect precisely the scenes or objects, with 2 kinds white balance of automatic one and manual one.
AWB---Automatic White Balance is divided into 2 kinds Automatic Tracking White balance (ATW, also called continuum white balance) and Automatic White balance Control (AWC).
Automatic Tracking White balance adjusts continuously following the change of scene color temperature, with range of 2800~6000K. It is most optimum that scene color temperature always change while recording with this way. The color can be showed most naturally. However, if there is little white color or even no this color of high color temperature objects and little dark scenes such as blue sky and white cloud or sunset, Automatic Tracking White balance can’t offer the best color effect.
Automatic White balance Control needs to take a reference from white object such as white wall and white paper by focusing the camera on them. Through the setup of menu or switch, it turns into the automatic way from the manual one, keeps the position for seconds or until the image getting white color, and turn back to the manual way to lock this white balance setup after the white balance on action and the setup has been saved in the camera memorizer until change again in need, with range of 2300~10000K. After this operation, even the camera power breaks the setup is not lost. This way of setting the white balance through button, is the most precise and reliable for most situation application..
Manual white balance works when the automatic white balance is turned off. With the manual device of regulating tone red or blue, you can regulate grades up to 107 levels by raising a level of red tune only or descending a blue one. Besides, some cameras also have the function of fixing the white balance on the levels of 3200k (the incandescent lampe level) or 5500k (the ordinary sunlight level)
Camera synchronization mode
There are 3 ways of camera synchronization mode: INT, LL and EXT
INT ---internal synchronous mode operates depending on which the crystal oscillator circuit in the camera produces the synchronized signal.
LL--- Line Locked, depends on the camera AC power source to synchronize the perpendicular movement. It is that the camera is synchronized with the power zero line.
EXT --- external synchronous mode depends on the synchronization signals transmitted from external synchronization signal generator to the camera corresponding input ports. The synchronization signals can be color-compound video signals or video black signals（VBS）, black-and-white- compound signals or synchronous compound signals（or video signal, VS）, compound vertical drive signals（or VD2）and compound video output signals.