Recompressing images to improve image retrieval performance

Virtually all images are stored in compressed form, most in (lossy) JPEG format. Compressing images however has been shown to cause a small but not negligible drop in performance for content-based image retrieval (CBIR) algorithms. In this paper, we show that it is possible to reverse this performance drop. We achieve this by what might at a first glance seem counter-intuitive, namely by compressing the images even more. In detail, what we perform is recompressing images (or rather re-quantising the DCT coefficients) to their lowest common image quality setting. We demonstrate, on a benchmark image retrieval database and using standard CBIR algorithms, that this results in improved image retrieval performance rivalling that of running the algorithms on uncompressed data.