A method and apparatus for detecting rare cells in a biological sample is disclosed. A color image of the sample is generated and the color image is decomposed into its color components. A first mask is then generated based upon a first color characteristic of the rare cells. At least one color component of the color image is filtered using the mask to produce at least a first composite image which contains features having the first color characteristic. At least a second mask is then generated based upon other color characteristics of the rare cells and at least the first composite image is filtered using at least the second mask to create at least a second composite image. The color and/or shape of features in the at least second composite image are analyzed and a list of locations of probable rare cells is generated from the color and/or shape analysis.