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Hamming embedding

Hamming embedding is an approximate nearest neighbor search technique used in image retrieval that maps high-dimensional local feature descriptors into compact binary signatures to improve matching accuracy. In visual bag-of-words representations, continuous image descriptors are partitioned into discrete visual words, which can introduce quantization errors by grouping dissimilar features into the same cluster. Hamming embedding addresses this by projecting the descriptor space assigned to each visual word into a lower-dimensional space and binarizing the resulting values using coordinate-wise thresholds. During retrieval, two descriptors are considered a valid match only if they share the same visual word and the Hamming distance between their binary signatures remains below a predefined threshold, effectively filtering out false positive matches while preserving high computational efficiency within inverted index structures.

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Hamming Embedding and Weak Geometric Consistency for Large Scale Image Search

Hamming Embedding and Weak Geometric Consistency for Large Scale Image Search

Hervé Jégou, Matthijs Douze, Cordelia Schmid

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Why you should read this

Presents Hamming embedding and weak geometric consistency to refine visual-word descriptor matching and filter geometrically inconsistent features directly within an inverted file, substantially increasing retrieval accuracy on million-scale image databases.

This paper improves recent methods for large scale image search. State-of-the-art methods build on the bag-of-features image representation. We, first, analyze bag-of-features in the framework of approximate nearest neighbor search. This shows the sub-optimality of such a representation for matching descriptors and leads us to derive a more precise representation based on 1) Hamming embedding (HE) and 2) weak geometric consistency constraints (WGC). HE provides binary signatures that refine the matching based on visual words. WGC filters matching descriptors that are not consistent in terms of angle and scale. HE and WGC are integrated within the inverted file and are efficiently exploited for all images, even in the case of very large datasets. Experiments performed on a dataset of one million of images show a significant improvement due to the binary signature and the weak geometric consistency constraints, as well as their efficiency. Estimation of the full geometric transformation, i.e., a re-ranking step on a short list of images, is complementary to our weak geometric consistency constraints and allows to further improve the accuracy.

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2026-09-16