@jtechlai/merge-images

merge-images

Easily composite images, no need to scribble on a canvas, can be used on webWorker

Using a canvas can sometimes be troublesome, especially when you only need to do some relatively simple tasks in the canvas context, like merging several images together. merge-images abstracts all the repetitive tasks into a single function call.

Images can be overlaid on each other and repositioned. The function returns a Promise, resolving to a base64 URI, Blob, or Blob URL. It supports both the browser and Node.js. When used in a browser, rendering tasks can be assigned to a web worker, improving rendering performance and preventing the main thread from being blocked and unresponsive during rendering.

Install

npm install --save @jtechlai/merge-images

or for quick testing:

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

Usage

With the following images:

body.png	eyes.png	mouth.png

You can do:

default use

import mergeImages from "merge-images";
// base64
mergeImages(["/body.png", "/eyes.png", "/mouth.png"]).then((b64) => (document.querySelector("img").src = b64));

// blob
mergeImages(["/body.png", "/eyes.png", "/mouth.png"], { outFormat: "blob" }).then(
  (blob) => (/*...blob*/)
);
// {data: ...., type: "image/png"}

// blob url
mergeImages(["/body.png", "/eyes.png", "/mouth.png"], { outFormat: "blob-url" }).then(
  (blobUrl) => (document.querySelector("img").src = blobUrl)
);
// blob:https://domain...

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

Positioning

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:

Opacity

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...

Dimensions

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:

Node.js Usage

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, Image } = require('canvas');

mergeImages(['./body.png', './eyes.png', './mouth.png'], {
  Canvas: Canvas,
  Image: Image
})
  .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.

webWorker Usage

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

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

One thing to note is that you need to provide a valid image source for Image. Note that you need to use a file path, not a relative URL as in the example.

validity: https://xxx.xxx.xxx/images.png✅
invalidity: ./examples/images/images.png❌

API

mergeImages(images, [options])

Returns a Promise which resolves to a base64 data URI

images

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.

options

Type: object

options.format

Type: 'image/png' | 'image/jpeg' | 'image/webp'
Default: 'image/png'

A DOMString indicating the image format.

options.quality

Type: number
Default: 0.92
Options: 0 ~ 1

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

options.width

Type: number
Default: undefined

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

options.height

Type: number
Default: undefined

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

options.background

Type: string
Default: #ffffff

Renders the background of the image. Defaults to #ffffff background, background is invalid when format is image/png

options.Canvas

Type: Canvas
Default: undefined

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

options.Image

Type: Image
Default: undefined

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

options.worker

Type: boolean
Default: true

Whether or not to use webWorker for the rendering process, note that you need to use new Worker() to call the use by yourself, check the examples catalog for examples.

options.outFormat

Type: "blob" | "blob-url" | "base64"
Default: base64

Output image format, default has "blob" | "blob-url" | "base64", use blob format, need to then convert to img readable format.

options.crossOrigin

Type: "anonymous" | "use-credentials" | "" | undefined
Default: undefined

The crossOrigin attribute that Image instances should use. e.g Anonymous to support CORS-enabled images.

License

MIT © JTechLai