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Figure 4 Fi g. 4a is a drawing of the différent events présent on a slide : from the left to the right, a carcinoma in situ cell, a normal intermediate, a granulocyte, a squamous cell covered by a leukocyte, an artefact (clump of cells or dust or staining artefact), and a bunch of degenerative leukocytes with reduced contrast. Fi g. 4b shows the profiles of ail these cells in a re¬ lief représentation. The three top-hats of fi g. 4c will be suffi¬ rent for the récognition of the carcinoma in situ cell and the setting aside of ail other cells and artefacts. The hat A detects the suspect cell and the granulocytes, but ignores the normal in¬ termediate cells because they are low-contrasted and also ignores the large artefact because the corresponding peak cannot enter into the hat A. Since the détection stage also detects granulocy¬ tes, it must be followed by an élimination procédure. The higher and narrower hat B detects highly contrasted leukocytes. If we eliminate ail leukocytes and parti cl es covered by leukocytes, there remain only the carcinoma in situ cells and the bunctes of de¬ generative leukocytes. Since these leukocytes présent a narrow white peak between themselves they may be detected by an upside down top-hat C, and can thus be eliminated. Finally, and theore-