Digital Image Processing for Scanning Acoustic Microscopy

Ahrmct-The use of a versatile digital image storage and processing system for scanning acoustic micrmcopy is described. In addition to the data capture and storage functions, different types of image processing functions of particular relevance to scanning acoustic microscopy have been incorporated These ipclude real-time grey scale enhancement and a variety of ofStine edge enhancement, spatial fdtering, and pseudocolor processing algorithms. These facilities can enhance particular aspects of the image or 6lter out unwanted artifacts. Typical results are presented. The further potential of digital processing for scanning acoustic microscopy is discussed. recurring problem associated with the use of imaging apparatus is the production of a display which will do justice to the quality of the data acquired and which is able to take advantage of the powerful electronic techniques for image storage and processing. The image processing described in this paper arose out of necessity, in the course of working with a relatively new form of imaging-scanning acoustic microscopy. Our approach has therefore been to present our results as an example of the application of general image processing techniques to a set of specific problems, arising from this form of microscopy. The scanning acoustic microscope (SAM) was first demonstrated by Quate and Lemons in 1973 [l]. Since then it has been developed sufficiently to allow its use as a tool for investigation of a wide range of materials as well as biological samples. It is particularly appropriate for the examination of the interior of optically opaque media [2] - [4]. In the basic operation of a SAM (reflection or transmission) [5], the object is immersed in a liquid (normally water) and place at the focal plane of an acoustic lens where it is interrogated by a focused ultrasonic beam. The object is subsequently scanned over the entire field of view in a raster manner so that the image is formed point by point. In a typical instrument the two orthogonal displacements of the scanner are measured by means of position encoders. Both amplitude and phase data may be recorded at each point in the scan. As the information and the position encoder outputs are produced in an analog form it was, until recently, accepted practice to resort