may be present which then specify the type light or dark and the orientation of the line end in any other cases the identification is terminated with an error message after type and orientation of the structure have been specified now the measuring of the same is started the measuring is subsequently described with reference to the line end serif opc structure shown in fig3 a and 3b the strategy of edge probing depends on the preceding identification in the following the measuring of a u201c dark upper line end u201d with line end serifs 500 is described the generalization to other structure types and orientations is trivial the first sampling is performed row wise in the x direction as shown in fig3 a wherein in fig3 a one starts at the bottom and proceeds row by row to the top to the line end see arrow 502 in fig3 a a row 504 is shown as an example if required also two or several rows each may be combined into one for each row the brightness profile 506 is extracted and from that using the threshold value s the positions of the two transitions light dark are determined with a greatest possible accuracy in the area of the line end serifs four transitions are present here only the outer two transitions are measured the sampling is terminated when no transition is visible any more in the profile i e at the upper end of the line end serifs thus the two edge courses left and right are obtained as a series of value pairs x left and x right firstly the maxima points of the structure lying farthest out are determined left and right then the minima point of the structure lying farthest in of the edge courses from.