The vast majority of images are stored in compressed JPEG format. When performing content-based image retrieval, faster feature extraction is possible when calculating them directly in the compressed domain, avoiding full decompression of the images. Algorithms that operate in this way calculate image features based on DCT coefficients and hence still require partial decoding of the image to arrive at these. In this paper, we introduce a JPEG compressed domain retrieval algorithm that is based not directly on DCT coefficients but on differences of these, which are readily available in a JPEG compression stream. In particular, we utilise solely the DC stream of JPEG files and make direct use of the fact that DC terms are differentially coded. We build histograms of these differences and utilise them as image features, thus eliminating the need to undo the differential coding as in other methods. In combination with a colour histogram, also extracted from DC data, we show our approach to give (to our knowledge) the best retrieval accuracy of a JPEG domain retrieval algorithm, outperforming other compressed domain methods and reaching a performance close to that of the best performing MPEG-7 descriptor.
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