1. A method of using a scanning microscope to rapidly form an image of a specimen, comprising: performing an initial scan or set of scans of a first area of the specimen composed of a first set of pixels to determine a first gray level for each of the pixels in the first set of pixels; analyzing the first gray levels of the pixels in the first set of pixels to identify first regions representing structures of interest in said first area, said first regions including fewer pixels than the number of pixels in the first set of pixels, wherein analyzing the first gray levels of the pixels includes comparing the first gray level of the pixels to thresholds, the thresholds depending on the gray level of adjacent pixels; performing additional scans of said first regions using the scanning microscope to determine second gray level values of only pixels of said first regions, the second gray level values being determined by integrating more scans than the number of scans used to determine the first gray levels, thereby improving an accuracy of the measured gray level value of pixels in the first regions while including fewer pixels in the additional scans; and progressively removing material from the specimen to reveal a new surface and each time a new surface is revealed, scanning a limited region of each new surface, the limited region being determined by the gray level of pixels in a previous scan.