Without control of the exposure the image brightness will change depending on the frequency of the EXSYNC signal supplied to the camera. This signal is usually derived from the speed at which the object is moving past the camera, for instance from an encoder. If no exposure control is used, the camera will collect light for the time between EXSYNC signals, so as the speed changes, the image brightness will change.
Setting the exposure time to the maximum time available between EXSYNC pulses when the system is running at its fastest will guarantee that the image brightness will remain constant, regardless of the speed of the object. The exposure time can be controlled either by an extra control signal, or by setting an exposure time in the camera.
Binning in single line scan cameras can traditionally only be done horizontally, where the sensor is clocked with two or more pixels being "binned" together. The accumulated charges from each pixel are combined, which reduces the horizontal resolution, but increases both the sensitivity and the signal-to-noise ratio.
Some of the latest CMOS single line sensors also feature a vertical binning feature. Here two lines are captured in sequence and then combined in the camera giving all the advantages of binning in both directions.