Active learning for object-based image classification using predefined training objects

• Published in: International journal of remote sensing 2018-05, Vol.39 (9), p.2746-2765
• Main Authors: Ma, Lei, Fu, Tengyu, Li, Manchun
• Format: Article
• Language: English
• Subjects: Active learning; Classification; classification uncertainty; Entropy; Entropy (Information theory); Evaluation; Image acquisition; Image analysis; Image classification; Image processing; Image resolution; Image segmentation; Machine learning; Mathematical models; mixed objects; Object recognition; object-based classification; Random sampling; Remote sensing; Sampling; segmentation; Stability; Stability analysis; Strategy; Technology; Training; Uncertainty
• ISSN: 0143-1161; 1366-5901
• DOI: 10.1080/01431161.2018.1430398

Object-based image analysis (OBIA) is a new remote-sensing-based image processing technology that has become popular in recent years. In spite of its remarkable advantages, the segmentation results that it generates feature a large number of mixed objects owing to the limitations of OBIA segmentation technology. The mixed objects directly influence the acquisition of training samples and the labelling of objects and thus affect the stability of classification performance. In light of this issue, this article evaluates the influence of classification uncertainty on classification performance and proposes a sampling strategy based on active learning. This sampling strategy is novel in two ways: (1) information entropy is used to evaluate the classification uncertainty of segmented objects; all segmented objects are classified as having zero or non-zero entropies, and the latter are arranged in terms of decreasing entropy. (2) Based on an evaluation of the influence of classification uncertainty on classification performance, an active learning technology is developed. A certain proportion of zero-entropy objects is acquired via random sampling used as seed training samples for active learning, non-zero-entropy objects are used as a candidate set for active learning, and the entropy query-by-bagging (EQB) algorithm is used to conduct active learning to acquire optimal training samples. In this study, three groups of high-resolution images were tested. The test results show that zero-entropy and non-zero-entropy objects are indispensable to the classifier, where the optimal range of the ratio of combination of the two is between 0.2 and 0.6. Moreover, the proposed sampling strategy can effectively improve the stability and accuracy of classification.