Global shutter
In the old days of photography, an image was simply taken by opening a box with a photosensitive film inside for a short time. More advanced photo cameras have a so-called "shutter" that opens after the release button has been pressed. Now, the light encounters the film and creates an image.
At the end of the exposure time (which has been set by the user before) the shutter closes and the film can be forwarded. Even today, many photo cameras are based on this exposure method. Only the film is substituted by a CMOS sensor or CCD sensor.
For cameras that output image sequences, like video cameras, camcorders or industrial USB cameras, FireWire cameras or GigE cameras, a mechanical shutter is a problem. Its speed is limited and it wears out. Thus, in this case it is preferable to use an electronic shutter.
CCD sensors have a global shutter
If the electronic shutter exposes the whole image sensor simultaneously, we have a so-called "global shutter". In contrast to this, most CMOS sensors are unable to expose the complete sensor simultaneously. They only expose it line by line, starting at the top. In this case, the shutter is called a rolling shutter.
It is in their nature that CCD sensors have a global shutter. However, meanwhile there are also the first CMOS sensors on the market with a global shutter. Using a global shutter is preferable for industrial cameras.
