Patent US 4,045,772

A white blood cell classification system is provided for detecting and classifying white blood cells in a peripheral blood smear. The system includes optical scanning means for scanning the blood smear, a microscope for directing the optical scanning means on the blood smear and means responsive to the scanning means for generating a signal corresponding to the color of the blood smear at the positions scanned. Color processing means are provided which are responsive to the signal for providing a signal representative of the relative darkness of the areas scanned. Detection means are provided which are responsive to the signal. The detection means includes a mask which is normally enabled by the nucleus of of all the white cells but which is not enabled by either platelets, foreign material or red cells in the blood smear. Finally, focusing means responsive to the detection means are provided for moving the position of the focus of the microscope to the optimum position after each white cell is detected.