ssim.js

What is ssim.js?

The ssim.js npm package is used for calculating the Structural Similarity Index (SSIM) between two images. SSIM is a method for measuring the similarity between two images, which is often used in the context of image quality assessment.

What are ssim.js's main functionalities?

Calculate SSIM between two images

This feature allows you to calculate the SSIM between two images. The `compare` function takes the paths to two images and returns a promise that resolves with the SSIM value.

const ssim = require('ssim.js');
const img1 = 'path/to/image1.png';
const img2 = 'path/to/image2.png';

ssim.compare(img1, img2).then(result => {
  console.log('SSIM:', result.ssim);
}).catch(err => {
  console.error(err);
});

Calculate SSIM for image buffers

This feature allows you to calculate the SSIM between two image buffers. The `compare` function can also take image buffers as input and returns a promise that resolves with the SSIM value.

const ssim = require('ssim.js');
const fs = require('fs');

const img1Buffer = fs.readFileSync('path/to/image1.png');
const img2Buffer = fs.readFileSync('path/to/image2.png');

ssim.compare(img1Buffer, img2Buffer).then(result => {
  console.log('SSIM:', result.ssim);
}).catch(err => {
  console.error(err);
});

Other packages similar to ssim.js

image-ssim

The image-ssim package is another library for calculating the Structural Similarity Index (SSIM) between two images. It provides similar functionality to ssim.js but may have different performance characteristics and API design.

sharp

The sharp package is a high-performance image processing library. While its primary focus is on image transformations (resizing, cropping, etc.), it also includes functionality for comparing images, including SSIM calculations. Sharp is known for its speed and efficiency.

gm

The gm (GraphicsMagick) package is a Node.js wrapper for the GraphicsMagick and ImageMagick tools. It provides a wide range of image processing capabilities, including image comparison and SSIM calculations. It is a more comprehensive tool for image manipulation compared to ssim.js.

README

SSIM.JS

Get a 0 to 1 score on how similar two images are

The closer SSIM is to 1 the higher the similarity. It correlates better with subjective ratings than other measures like PSNR and MSE. For instance:

Original, MSE = 0, SSIM = 1	MSE = 144, SSIM = 0.988	MSE = 144, SSIM = 0.913
MSE = 144, SSIM = 0.840	MSE = 144, SSIM = 0.694	MSE = 142, SSIM = 0.662

Table extracted from http://www.cns.nyu.edu/~lcv/ssim/

🖥 Install

npm install ssim.js

You can also use the web version directly from unpkg's CDN: https://unpkg.com/ssim.js@{{version}}/dist/ssim.web.js.

📝 Usage

Check out the playground for node and web usage examples.

SSIM.js takes in 2 image buffers and optional options parameter. You can find all options available here.

For examples on how to implement image loading strategies for both node and the web, check out this wiki page.

import ssim from "ssim.js";

const img1 = loadImage("./img1.jpg");
const img2 = loadImage("./img2.jpg");

const { mssim, performance } = ssim(img1, img2);

console.log(`SSIM: ${mssim} (${performance}ms)`);

📖 Documentation

If you run into any issues or want a more info, check the wiki.

The code is fully documented but feel free to create an issue here if you have any questions.

🏁 Metrics

Process	Status
Versioning
Dependencies

💡 Credits

This project is a direct port of algorithms published by Wang, et al. 2004 on "Image Quality Assessment: From Error Visibility to Structural Similarity". The original Matlab scripts are available here with their datasets. To view the steps taken to validate ssim.js results, check the wiki.

The current (default) implementation uses the Weber algorithm, originally developed by Dan Weber, 2020 at notatypical.agency.