Goodpoint: unsupervised learning of key point detection and description

Abstract

Subject of Research. The paper presents the study of algorithms for key point detection and description, widely used in computer vision. Typically, the corner detector acts as a key point detector, including neural key point detectors. For some types of images obtained in medicine, the application of such detectors is problematic due to the small number of detected key points. The paper considers a problem of a neural network key point detector training on unlabeled images. Method. We proposed the definition of key points not depending on specific visual features. A method was considered for training of a neural network model meant for detecting and describing key points on unlabeled data. The application of homographic image transformation was basic to the method. The neural network model was trained to detect the same key points on pairs of noisy images related to a homographic transformation. Only positive examples were used for detector training, just points correctly matched with features produced by the neural network model for key point description. Main Results. The unsupervised learning algorithm is used to train the neural network model. For the ease of comparison, the proposed model has a similar architecture and the same number of parameters as the supervised model. Model evaluation is performed on the three different datasets: natural images, synthetic images, and retinal photographs. The proposed model shows similar results to the supervised model on the natural images and better results on retinal photographs. Improvement of results is demonstrated after additional training of the proposed model on images from the target domain. This is an advantage over a model trained on a labeled dataset. For comparison, the harmonic average of such metrics is used as: the accuracy and the depth of matching by descriptors, reproducibility of key points and image coverage. Practical Relevance. The proposed algorithm makes it possible to train the neural network key point detector together with the feature extraction model on images from the target domain without costly dataset labeling and reduce labor costs for the development of the system that uses the detector.