vitali-fedulov / imagehash2

Fast image similarity search with hash tables (Golang). Version 2 (LATEST)

Fast similar image search with Go (LATEST version)

Resized and near-duplicate image search for very large image collections (thousands, millions, and more). The package generates 'real' hashes to be used in hash-tables, and consumes very little memory. It is recommended to cross-check the similarity result with more precise images4 package.

Demo (a usage scenario for image similarity search).

Algorithm for nearest neighbour vector search by vector quantization.

Go doc.

Major (semantic) versions have their own repositories and are mutually incompatible:

Major version	Repository	Comment
2	imagehash2 (this)	recommended, with improved precision
1	imagehash	as fast, but has a generalization defect

Parameters

The most important parameter is numBuckets. It defines granularity of hyper-space quantization. The higher the value, the more restrictive the comparison is. And, when used together with images4 package, higher numBuckets considerably accelerates the search process, because fewer image ids fall into a single quantization cell.

The second parameter is epsilon, which can be safely set to 0.25.

Example of comparison for 2 photos

The demo shows only the hash-based similarity comparison (without making actual hash table). But the hash table, typically a Golang map, is implied in full implementation.

package main

import (
	"fmt"
	"github.com/vitali-fedulov/imagehash2"
	"github.com/vitali-fedulov/images4"
)

const (
	// Recommended initial parameters.

	// Increase this value to get higher precision.
	numBuckets = 4

	// No need to change epsilon value.
	epsilon = 0.25
)

func main() {

	// Open and decode photos (skipping error handling for clarity).
	img1, _ := images4.Open("1.jpg")
	img2, _ := images4.Open("2.jpg")

	// Icons are compact image representations needed for comparison.
	icon1 := images4.Icon(img1)
	icon2 := images4.Icon(img2)

	// Hash table values.

	// Value to save to the hash table as a key with corresponding
	// image ids. Table structure: map[centralHash][]imageId.
	// imageId is simply an image number in a directory tree.
	// And centralHash type is uint64.
	centralHash := imagehash2.CentralHash9(icon1, epsilon, numBuckets)

	// Hash set to be used as a query to the hash table. Each hash from
	// the hashSet has to be checked against the hash table.
	hashSet := imagehash2.HashSet9(icon2, epsilon, numBuckets)

	foundSimilarImage := false

	// Checking hash matches. In full implementation to search in many
	// images, this will be done on the following hash table of type
	// map[centralHash][]imageId. Where centralHash type is uint64.
	for _, hash := range hashSet {
		if centralHash == hash {
			foundSimilarImage = true
			break
		}
	}

	// Comparison result.
	if foundSimilarImage {

		fmt.Println("Images are *approximately* similar.")

		// It is recommended to cross-check the result with
	        // the higher-precision func Similar from package images4.
		if images4.Similar(icon1, icon2) == true {
			fmt.Println("Images are similar")
		}

	} else {
		fmt.Println("Images are distinct.")
	}

}