A method of removing a potential false positive result in a stained sample. The method includes the steps of: acquiring a spectral image set of a stained sample; performing linear spectral unmixing of the spectral image set to obtain a plurality of rule images; calculating an error image for the stained sample; thresholding at least one of the plurality of rule images, wherein thresholding is based on the error image; and removing a potential false positive result from the at least one of the plurality of rule images based on thresholding.