ElasticHash

Introduction

ElasticHash implements efficient similarity search by using a two-stage method for efficiently searching binary hash codes using Elasticsearch. In the first stage, a coarse search based on short hash codes is performed using multi-index hashing and ES terms lookup of neighboring hash codes. In the second stage, the list of results is re-ranked by computing the Hamming distance on long hash codes.

The only requirement ist that binary codes to be indexed need to be 256 bits long as currently only 256 bit codes are supported.

For a whole image similarity search system, including model training and model serving, see https://github.com/umr-ds/ElasticHash.

Install

pip install elastichash

Usage

• Create an Elastisearch client to use it with ElasticHash

  es = Elasticsearch(elasticsearch_endpoint)
  eh = ElasticHash(es)
  

• New items can be added by calling add(code) where code can be a list, string or numpy array together with additional fields

  eh.add(code, additional_fields={"image_path": "/path/to/an/image"})
  

• After adding a suffiently large amount of codes (e.g. 10,000), decorrelate() needs to be called to rearrange the binary hashcode permutations
• To search documents by their hash code use search(code)