A method of microcomputer‐aided two‐dimensional densitometry: An apparatus equipped with a chargecoupled device camera, and an algorithm of microcomputer programming

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Abstract
A simple apparatus and a convenient program for evaluation of two‐dimensional electrophoretograms have been developed. The hardware system comprises a charge‐coupled device (CCD) camera, four pages of frame memory (FM), a page of display memory (DM), a video‐monitor cathode‐ray tube (CRT), a digitizer (DIG) and two ports of parallel interfaces (PIO). A small desk‐top microcomputer is connected to the apparatus via the interfaces. The system program named frame‐imagememory controller (FIMC) has been developed under an assembler of the microcomputer. FIMC is a package of subroutines, and utility programs for two‐dimensional densitometry can be written in BASIC language simply with the help of FIMC. Unevenness of basal gray level, caused by the nonuniformity of illumination in the camera's field of view, is eliminated from the pixel data by a method of blank subtraction. Background gray level, caused by protein staining procedures, is corrected by a method of local background subtraction. The two‐dimensional densitometry system, equipped with a CCD camera, is applicable not only to transparent gels but also to opaque membranes, and it shows a high reliability in optical measurement in the range of 0–2 O.D.