Abstract-Efficient defect classification is one of the most important preconditions to achieve online quality inspection for hot-rolled strip steels. It is extremely challenging owing to various defect appearances, large intra-class variation, ambiguous inter-class distance, and unstable gray values. In this paper, a generalized completed local binary patterns (GCLBP) framework is proposed. Two variants of improved completed local binary patterns (ICLBP) and improved completed noise-invariant local-structure patterns (ICNLP) under the GCLBP framework are developed for steel surface defect classification. Different from conventional LBP variants, descriptive information hidden in nonuniform patterns is innovatively excavated for better defect representation. This work focuses on the following aspects: First, a lightweight searching algorithm is established for exploiting the dominant nonuniform patterns (DNUPs). Second, a hybrid pattern code mapping mechanism is proposed to encode all the uniform patterns and DNUPs. Third, feature extraction is carried out under the GCLBP framework. Finally, histogram matching is efficiently accomplished by simple nearest neighbor classifier (NNC). The classification accuracy and time-efficiency are verified on a widely recognized texture database (Outex) and a real-world steel surface defect database (NEU). The experimental results promise that the proposed method can be widely applied in online AOI instruments for hot-rolled strip steel.Index Terms-Surface defects, image classification, hot-rolled strips, local binary patterns (LBP), automatic optical inspection (AOI) instrument.