1. A method for defect analysis, comprising: identifying, by a computer system, respective single-class classifiers for a plurality of defect classes, the plurality of defect classes characterized by respective ranges of inspection parameter values, each single-class classifier being configured for a respective class to identify defects belonging to the respective class based on the inspection parameter values, while identifying the defects not in the respective class as unknown defects; identifying, by the computer system, a multi-class classifier configured to assign each defect to one of the plurality of the defect classes based on the inspection parameter values; receiving, by the computer system inspection data with respect to a defect found in a sample; and automatically applying both the single-class and multi-class classifiers to the inspection data, using the computer system, to assign the defect to one of the defect classes.