imgsim

README

Imgsim

Imgsim is a library allows you to compute a fast perceptual hashes of an image. These hashes can then be used to compare images for similarity. Similar looking images will get similar perceptual hashes. Unlike cryptographic hashes that would be very different for images with slight differences. This makes them suitable to compare how similar images are.

Average hash

An average hash is an example of a perceptual hash.

For an introduction see: Average hash

Difference hash

Difference hashes are said to be more resillient to changes in the image then the Average hash.

For an introduction see: Difference hash

Installation

The package is go-gettable: go get -u github.com/Nr90/imgsim.

Example

package main

import (
	"fmt"
	"image/png"
	"os"

	"github.com/Nr90/imgsim"
)

func main() {
	imgfile, err := os.Open("assets/gopher.png")
	defer imgfile.Close()
	if err != nil {
		panic(err)
	}
	img, err := png.Decode(imgfile)
	if err != nil {
		panic(err)
	}
	ahash := imgsim.AverageHash(img)
	fmt.Println(ahash)
	dhash := imgsim.DifferenceHash(img)
	fmt.Println(dhash)
}

Documentation

Overview

Package imgsim is a library allows you to compute a fast perceptual hashes of an image. These hashes can then be used to compare images for similarity. Similar looking images will get similar perceptual hashes, unlike cryptographic hashes that would be very different for images with slight differences. This makes them suitable to measure how similar images are.

Index

• func Distance(a, b Hash) int
• type Hash
  • func AverageHash(img image.Image) Hash
  • func DifferenceHash(img image.Image) Hash
  • func (h Hash) String() string

Functions

func Distance

func Distance(a, b Hash) int

Distance calculates the number of different bits in the hash

Types

type Hash

type Hash uint64

Hash contains the perceptual hash stored as bits in a 64 bit unsigned integer.

func AverageHash

func AverageHash(img image.Image) Hash

AverageHash calculates the average hash of an image. First the image is resized to 8x8. Then it is converted to grayscale. Lastly the average hash is computed.

func DifferenceHash

func DifferenceHash(img image.Image) Hash

DifferenceHash calculates the average hash of an image. First the image is converted to grayscale Then it is resized to 9x8. Lastly the average hash is computed.

func (Hash) String

func (h Hash) String() string