browser-image-resizer

Introduction

This library allows for cross-browser image downscaling and resizing utilizing <canvas>. Note that this is browser-only utility and will not work in Node.js.

Installation

NPM/Yarn

• npm install git+https://github.com/misskey-dev/browser-image-resizer
• yarn add git+https://github.com/misskey-dev/browser-image-resizer

Usage

NPM/Yarn

Promises

import { readAndCompressImage } from 'browser-image-resizer';

const config = {
  quality: 0.5,
  maxWidth: 800,
  maxHeight: 600,
  debug: true
};

// Note: A single file comes from event.target.files on <input>
readAndCompressImage(file, config)
  .then(resizedImage => {
    // Upload file to some Web API
    const url = `http://localhost:3001/upload`;
    const formData = new FormData();
    formData.append('images', resizedImage);
    const options = {
      method: 'POST',
      body: formData
    };

    return fetch(url, options);
  })
  .then(result => {
    // TODO: Handle the result
    console.log(result);
  });

Async/Await

import { readAndCompressImage } from 'browser-image-resizer';

const config = {
  quality: 0.7,
  width: 800,
  height: 600
};

// Note: A single file comes from event.target.files on <input>
async function uploadImage(file) {
  try {
    let resizedImage = await readAndCompressImage(file, config);

    const url = `http://localhost:3001/upload`;
    const formData = new FormData();
    formData.append('images', resizedImage);
    const options = {
      method: 'POST',
      body: formData
    };

    let result = await fetch(url, options);

    // TODO: Handle the result
    console.log(result);
    return result;
  } catch (error) {
    console.error(error);
    throw(error);
  }
}

readAndCompressImage(file, config) => Promise

Inputs

• file: A File object, usually from an <input>
• config: See below

| Property Name | Purpose | Default Value | | ------------- |-------------| -----:| | quality | The quality of the image | 0.5 | | maxWidth | The maximum width for the downscaled image | 800 | | maxHeight | The maximum height for the downscaled image | 600 | | debug | console.log image update operations | false | | mimeType | specify image output type other than jpeg | 'image/jpeg' |

Outputs

A Promise that yields an Image Blob

Output Image Specification

The output image is derived from canvas.toDataURL.

• EXIF and other metadata will be erased.
• Rotation will be automatically corrected.
  • It is based on the specifications of recent versions of modern browsers and may not work with older browsers.
  • See https://github.com/w3c/csswg-drafts/issues/4666#issuecomment-610962845
  • Firefox support seems to be available from version 78. by mei23
• Color profile is srgb. Firefox 97 does not attach the ICC profile, but Chrome does.
• You can specify image/webp as the mimeType, but Safari will ignore quality (treated as 1).