Automatic image annotation by a loosely joint non‐negative matrix factorisation

Abstract

Nowadays, the number of digital images has increased so that the management of this volume of data needs an efficient system for browsing, categorising and searching. Automatic image annotation is designed for assigning tags to images for more accurate retrieval. Non‐negative matrix factorisation (NMF) is a traditional machine learning technique for decomposing a matrix into a set of basis and coefficients under the non‐negative constraints. In this study, the authors propose a two‐step algorithm for designing an automatic image annotation system that employs the NMF framework for its first step and a variant of K‐nearest neighbourhood as its second step. In the first step, a new multimodal NMF algorithm is proposed to extract the latent factors which reflect the content of images. This is done by jointly factorising the visual and textual data feature matrices so that they have close representation, although not necessarily the same. In the second step, after mapping images to the latent factors space a few tags are predicted for the new images based on a weighted average of similar data. They evaluated the performance of the proposed method and compared it to the state‐of‐the‐art literature. Comparison results demonstrate the effectiveness and potential of the proposed method in image annotation applications.