An image intensifier tube which obviates problems with stray reflections caused by bright lights utilizes an antireflection coating in the form of an interference filter on the cathode window. A user interface with at least two regions is output for display to a user. In this way, while the speed of packaging operation can be increased and the rate of replacement of the gas can be maintained at a high value, production of defective bagged products which would result from the biting of the articles in the seals consequent upon blow-up of some of the articles within the bag-shaped packaging material can be prevented advantageously. The black level calibration circuit determines a black level offset according to the first optical black information, and determines a black level calibration value for calibrating the active pixel information. The reading and writing of the data sub-blocks is evenly distributed between at least two area of a memory.