Scan Conversion and Noise Reduction Using a Framestore

Abstract

Analogue scan conversion has been incorporated into several dedicated STEM systems1 to produce a composite video signal for display on a TV monitor, with the image updated at the microscope frame scan frequency. Greater flexibility is provided by completely digital methods which have proved particularly useful at relatively slow scan rates2 and recently an experimental 6-bit intensity system for a TEM TV camera has been described by Herrmann3. This paper reports an experimental adaptation of a commercially available (Microconsultants) broadcast framstore system to acquire, process and display images, and potentially also other data, with 8-bit intensity resolution over a wide range of scan rates. The unit that was adapted for this purpose is a development of the standard 'Intellect' system which uses digitally controlled 512x512 sampling of the normal analogue signals at a rate which can be selected to be suitable for use with either TV or slow scans of the record type. A simple hardware modification to the input interface permits intermediate rates such as SEM visual images which have proved to be the most useful ranges for the initial applications. The framestore has been interfaced to a JEM100C ASID-4D Temscan and also to an HVEM TV camera used for recording dynamic experiments. Interfacing to the SEM control box was straightforward using the display blanking pulses with 50Ω line drivers to synchronise the rates of sampling the line and frame scans. The original system was designed to accept only inputs to NTSC TV standards with which the TV camera is directly compatible.