Abstract: In this circuit, video signals with a continuously increasing or decreasing amplitude are applied to the signal input of a threshold difference comparator at whose reference inputs selectively determined high and low threshold signals are applied. The output of the threshold difference comparator is applied at the first input of a threshold AND gate having a second input connected to a clock. The output of the threshold AND gate supplies a clock pulse sequence which has a duration corresponding with the time during which the input video signal has an amplitude which continuously increases or decreases from one of the threshold reference amplitudes to the other. The clock pulse sequences contained in successive measuring intervals have their respective pulses counted by a counter, and are stored in a buffer. A measurement series is performed corresponding to different focus settings, optimum focus adjustment being achieved when a minimum count of clock pulses in a clock pulse sequence is obtained.

Abstract: Method and apparatus for automatic optical inspection of a substantially two-dimensional pattern using digital image processing techniques are described. In a first processing step, all regions of a digitized stored image derived from the two-dimensional pattern are scanned for edges or lines, that is, transitions between regions having optically different characteristics. The scanned edge regions are marked in the image storage. In a subsequent second processing step all non-marked regions of the image storage are scanned and tested for the presence of permissible grey levels. A meander-shaped scanning track is used for scanning the edge or lined regions. The apparatus for implementing this method includes special latch circuitry for eliminating the further processing of marked regions, thus increasing the overall speed at which the two-dimensional pattern can be optically inspected.