Backlight Compensation
Backlight compensation can get ideal exposure of object which is in front of the strong luminance background, no matter object moving to center, top, bottom, left, right or any other position of screen. For a common WDR (wide dynamic range) camera, it has an electronic shutter with only 1/60 second speed and has an aperture with only F2.0. However, if there is a strong luminous background or luminous point, camera will consider them into the determination of exposure grade. Actually speaking, this is not a good method to get ideal exposure, because when electronic shutter is moving fast, aperture will be closed and lead to too dark to see object. In order to solve this problem, a skill which is called backlight compensation is widely applied to many cameras according to the weighting theory of area. By such method, image is firstly divided into 7 pieces or 6 pieces (two regions are repeated), and each region can respectively weight so as to calculate exposure grade. For example, central part is weighted as 9 times as other parts. Thus the central object is watched clearly, because exposure grade is mainly depended by luminance of central part. Nevertheless, there is a big weakness that if main object moves from central position to other positions of image, object will become very dark, because it is put aside by weighted region.
