Abstract: A technique for measuring the distance between the edges of a feature positioned on a substrate wherein the feature is illuminated with light on either side of the edges and the light intensities at either side of each of the edges are detected and are balanced at the detected light intensities regions sufficiently removed from the edges to prevent an adverse diffractive effect thereon so as to produce regions of minimum light intensity at the edges, the positions of which can be determined and the distance between said regions of minimum intensity can be measured.

Abstract: A radio data system transmits message groups comprising four blocks of which the first block always carries the program identification code for the transmitting network (P1(TN)). One type of message group, identified by a corresponding group type code (GT) in a second block always carries a program identification code for another network (PI(ON) in a fourth block and carries various corresponding items of information in a third block. Which of these various items is in the third block is identified by a user code (UC) in the second block. The items of information in the third block may in particular include alternative frequency codes for the other network identified in the fourth block.

Abstract: A method and apparatus for processing image signals read out from a recording medium in which different kinds of image signals are stored. One frame of the image signals from the recording medium is stored in sequence until a time at which the kind of image signals is switched. The stored image signals are read out and the level thereof are gradually decreased from the switched time, and simultaneously the level of the image signals read out from the recording medium subsequent to the stored image signals are gradually increased. Then, the level of the decreased image signals are added with the level of the increased image signals.