Easily compose images together without messing around with canvas

Canvas can be kind of a pain to work with sometimes, especially if you just need a canvas context to do something relatively simple like merge some images together. merge-images abstracts away all the repetitive tasks into one simple function call.

Images can be overlaid on top of each other and repositioned. The function returns a Promise which resolves to a base64 data URI. Supports both the browser and Node.js.

npm install --save merge-images

or for quick testing:

<script src="https://unpkg.com/merge-images"></script>

With the following images:

/body.png	/eyes.png	/mouth.png

You can do:

import mergeImages from 'merge-images';

mergeImages(['/body.png', '/eyes.png', '/mouth.png'])
  .then(b64 => document.querySelector('img').src = b64);
  // data:image/png;base64,iVBORw0KGgoAA...

And that would update the img element to show this image:

Those source png images were already the right dimensions to be overlaid on top of each other. You can also supply an array of objects with x/y co-ords to manually position each image:

mergeImages([
  { src: 'body.png', x: 0, y: 0 },
  { src: 'eyes.png', x: 32, y: 0 },
  { src: 'mouth.png', x: 16, y: 0 }
])
  .then(b64 => ...);
  // data:image/png;base64,iVBORw0KGgoAA...

Using the same source images as above would output this:

The opacity can also be tweaked on each image.

mergeImages([
  { src: 'body.png' },
  { src: 'eyes.png', opacity: 0.7 },
  { src: 'mouth.png', opacity: 0.3 }
])
  .then(b64 => ...);
  // data:image/png;base64,iVBORw0KGgoAA...

By default the new image dimensions will be set to the width of the widest source image and the height of the tallest source image. You can manually specify your own dimensions in the options object:

mergeImages(['/body.png', '/eyes.png', '/mouth.png'], {
  width: 128,
  height: 128
})
  .then(b64 => ...);
  // data:image/png;base64,iVBORw0KGgoAA...

Which will look like this:

Usage in Node.js is the same, however you'll need to also require node-canvas and pass it in via the options object.

const mergeImages = require('merge-images');
const Canvas = require('canvas');

mergeImages(['./body.png', './eyes.png', './mouth.png'], {
  Canvas: Canvas
})
  .then(b64 => ...);
  // data:image/png;base64,iVBORw0KGgoAA...

One thing to note is that you need to provide a valid image source for the node-canvas Image rather than a DOM Image. Notice the above example uses a file path, not a relative URL like the other examples. Check the node-canvas docs for more information on valid Image sources.

Returns a Promise which resolves to a base64 data URI

Type: array
Default: []

Array of valid image sources for new Image().
Alternatively an array of objects with x/y co-ords and src property with a valid image source.

Type: object

Type: string
Default: 'image/png'

A DOMString indicating the image format.

Type: number
Default: 0.92

A number between 0 and 1 indicating image quality if the requested format is image/jpeg or image/webp.

Type: number
Default: undefined

The width in pixels the rendered image should be. Defaults to the width of the widest source image.

Type: number
Default: undefined

The height in pixels the rendered image should be. Defaults to the height of the tallest source image.

Type: Canvas
Default: undefined

Canvas implementation to be used to allow usage outside of the browser. e.g Node.js with node-canvas.

MIT © Luke Childs