A method and apparatus are provided for selecting and analyzing a subpopulation of cells or cell objects for a certain parameter such as DNA using image analysis means. The cells are first stained with an alkaline phosphatase technique including a monoclonal antibody specific to a protein in at least one of the cell's cytoplasm or on a cell membrane, thereby marking any cells including the protein as to type. A second staining of the DNA in the nucleus is accomplished by a Feulgen technique that destroys the cell cytoplasm. After the staining and marking, the cells may then be gated using the image analysis means on the visual parameter such as colored DNA or colored antigen into a subpopulation that is to be measured. The selected cells may then be examined by digital image processing and measured for a parameter such as a true actual measurement of DNA in picograms. A quantitation of the measured parameter may be generated and provided.