Image classification using spatial pyramid robust sparse coding

Recently, the sparse coding based codebook learning and local feature encoding have been widely used for image classification. The sparse coding model actually assumes the reconstruction error follows Gaussian or Laplacian distribution, which may not be accurate enough. Besides, the ignorance of spatial information during local feature encoding process also hinders the final image classification performance. To address these obstacles, we propose a new image classification method by spatial pyramid robust sparse coding (SP-RSC). The robust sparse coding tries to find the maximum likelihood estimation solution by alternatively optimizing over the codebook and local feature coding parameters, hence is more robust to outliers than traditional sparse coding based methods. Additionally, we adopt the robust sparse coding technique to encode visual features with the spatial constraint. Local features from the same spatial sub-region of images are collected to generate the visual codebook and encode local features. In this way, we are able to generate more discriminative codebooks and encoding parameters which eventually help to improve the image classification performance. Experiments on the Scene 15 dataset and the Caltech 256 dataset demonstrate the effectiveness of the proposed spatial pyramid robust sparse coding method.

► We propose a new image classification method by spatial pyramid robust sparse coding. ► Images are spatially partitioned into sub-regions for codebook generation and local feature encoding. ► We alternatively optimize over codebook and encoding parameters by maximum likelihood. ► We achieve comparable performances with other methods on two public datasets.