ABSTRACT
Nothing short of a revolution has occurred with the recent appearance of laser printers, and others of comparable refinement (Fig. 107). Now it is possible to create a genuine half-tone picture by means of dots of different sizes, exactly as a photograph is reproduced in a book or newspaper-with the added bonus of publication-quality lettering. Rather than using dots of one size in randomized positions, as with dot density, the halftone dots are on a regular but very fine grid and are varied in size. This gives a less ‘scruffy’ effect and cleaner backgrounds which, combined with a continuous grey scale make it possible to show as wide a range of data from low to high as is required, so that positive and negative anomalies can be displayed clearly in a single plot. The type of plot, discussed above, in which normal positive anomalies due to pits and ditches are shown dark, alongside the weak negative anomalies of building foundations in white, is normally more effective than with dot density. Emphasis is added to weak anomalies by the reverse anomalies that accompany them. The full sensitivity range of modern instruments, especially magnetometers, can be fully exploited to reveal subtleties never before seen in archaeological prospecting.
