Digital imagery for making plates

Abstract. Although the resolution and depth of focus provided by scanning electron microscopy (SEM) revolutionized the examination of several groups of microfossils, conventional photographic techniques are normally outlined in instructions for preparation of micrographs for publication (Whittaker & Hodgkinson, 1991). While the quality of results attainable by following these methods is very high, digital image recording and processing techniques are now well developed and readily available. This note outlines some advantages of digital techniques in the preparation of SEM images for publication.

DIGITAL RECORDING

Secondary electron and other detectors attached to the SEM produce analogue (waveform) signals. In early instruments only these analogue signals were processed and displayed. Modern designs quantize signals from the detector as pixels (picture elements) which represent grey levels along scan lines. Pixel information is processed by the SEM on-board computer and saved as an image file. Importantly, the basic hardware to convert the analogue signal to digital form is simple and can be readily retro-fitted to early instruments. Our Philips PSEM 500 was adapted to record 128 grey levels at 800 pixels/line over 600 lines/frame, a minimum specification for professional work. Many micropalaeontologists will find that their SEM laboratories can supply digital files at higher resolutions. However, an essential point is to work with images recorded digitally directly from the SEM video channel, so avoiding potential degradation due to scanning of images recorded on film from the SEM monitors.

DIGITAL PROCESSING

I use Photostyler (a PC image editor by Aldus Corp.) for plate composition. It resembles. . .