Writer Identification and Writer Retrieval Based on NetVLAD with Re-ranking

This paper addresses writer identification and retrieval which is a challenging problem in the document analysis field. In this work, a novel pipeline is proposed for the problem by employing a unified neural network architecture consisting of the ResNet-20 as a feature extractor and an integrated NetVLAD layer, inspired by the vectors of locally aggregated descriptors (VLAD), in the head of the latter part. Having defined this architecture, triplet semi-hard loss function is used to directly learn an embedding for individual input image patches. Generalised max-pooling is used for the aggregation of embedded descriptors of each handwritten image. In the evaluation part, for identification and retrieval, re-ranking has been done based on query expansion and $k$-reciprocal nearest neighbours, and it is shown that the pipeline can benefit tremendously from this step. Experimental evaluation shows that our writer identification and writer retrieval pipeline is superior compared to the state-of-the-art pipelines, as our results on the publicly available ICDAR13 and CVL datasets set new standards by achieving 96.5% and 98.4% mAP, respectively.