SACCAS. A semiautomated counting machine with an accommodating threshold selector.

SACCAS, the Stanford Automated Cell/Colony Autoradiograph Scanner, is a system designed to expedite the analysis of autoradiographs made from tumor cells. Cells are viewed for grain counting under reflected darkfield illumination. The image is transmitted to the computer's digitizing hardware via a TV camera. The ability of this machine to count tritium grains accurately and reproducibly depends upon proper thresholding of grains from the underlying nucleus. Thresholding is performed automatically using a gray-value-histogram evaluation algorithm. For 489 nuclei, the grain counts using SACCAS compared favorably to the manual counts of two experienced operators. The coefficients of variation were 12.8% between two manual counts and 13.0% between two machine counts. A plot of mean manual against mean SACCAS counts showed a correlation coefficient of 0.98.