gif-encoder-2

Encode GIFs with Node.js

Contents

• Installation
• Overview
• Usage
  • Constructor
  • Methods
• Examples
  • Canvas Animation
  • Sequencial Images
• Algorithms
• Optimizer
• Progess Event

Installation

npm install gif-encoder-2

Overview

This library builds on top of previous JavaScript GIF encoders including jsgif and gifencoder.

This library adds the Octree quantization algorithm as an alternative to the original NeuQuant algorithm.

This library adds a simple optimizer to speed up overall processing time of both algorithms.

This library adds a progress event.

This library is designed to be used in a Node environment, including the Electron renderer process. Node Canvas can be a useful peer library but isn't required. The [HTML Canvas API] can be used in Electron.

Usage

Constructor

GIFEncoder(width, height, algorithm, useOptimizer, totalFrames)

Parameter	Type	Description	Required	Default
width	number	the width of images in pixels	yes	n/a
height	number	the height of images in pixels	yes	n/a
algorithm	string	neuquant or octree	no	neuquant
useOptimizer	boolean	enables/disables optimizer	no	false
totalFrames	number	total number of images	no	0

const encoder = new GIFEncoder(500, 500)
const encoder = new GIFEncoder(1200, 800, 'octree', false)
const encoder = new GIFEncoder(720, 480, 'neuquant', true, 20)

Methods

Method	Parameter	Description	Notes
start	n/a	Starts the encoder	n/a
addFrame	Canvas Context	Adds a frame to the GIF	n/a
setDelay	number	Number of milliseconds to display frame	Can be set once or per frame
setFramesPerSecond	number	Number of frames per second to display	Another way to set delay
setQuality	number 1-30	Neuquant quality	1 is best/slowest
setThreshold	number 0-100	Optimizer threshold percentage	Color table reused if current frame matches previous frame
setRepeat	number >= 0	Number of loops GIF does	0 is forever, anything else if literal number of loops
finish	n/a	Stops the encoder	Call after all frames are added

Examples

Canvas Animation

Draw a square that changes color as it moves.

const GIFEncoder = require('gif-encoder-2')
const { createCanvas } = require('canvas')
const { writeFile } = require('fs')
const path = require('path')

const size = 200
const half = size / 2

const canvas = createCanvas(size, size)
const ctx = canvas.getContext('2d')

function drawBackground() {
  ctx.fillStyle = '#ffffff'
  ctx.fillRect(0, 0, size, size)
}

const encoder = new GIFEncoder(size, size)
encoder.setDelay(500)
encoder.start()

drawBackground()
ctx.fillStyle = '#ff0000'
ctx.fillRect(0, 0, half, half)
encoder.addFrame(ctx)

drawBackground()
ctx.fillStyle = '#00ff00'
ctx.fillRect(half, 0, half, half)
encoder.addFrame(ctx)

drawBackground()
ctx.fillStyle = '#0000ff'
ctx.fillRect(half, half, half, half)
encoder.addFrame(ctx)

drawBackground()
ctx.fillStyle = '#ffff00'
ctx.fillRect(0, half, half, half)
encoder.addFrame(ctx)

encoder.finish()

const buffer = encoder.out.getData()

writeFile(path.join(__dirname, 'output', 'beginner.gif'), buffer, error => {
  // gif drawn or error
})

Sequencial Images

Create a function that reads a directory of images and turns them into a GIF.

const GIFEncoder = require('gif-encoder-2')
const { createCanvas, Image } = require('canvas')
const { createWriteStream, readdir } = require('fs')
const { promisify } = require('util')
const path = require('path')

const readdirAsync = promisify(readdir)
const imagesFolder = path.join(__dirname, 'input')

async function createGif(algorithm) {
  return new Promise(async resolve1 => {
    // read image directory
    const files = await readdirAsync(imagesFolder)

    // find the width and height of the image
    const [width, height] = await new Promise(resolve2 => {
      const image = new Image()
      image.onload = () => resolve2([image.width, image.height])
      image.src = path.join(imagesFolder, files[0])
    })

    // base GIF filepath on which algorithm is being used
    const dstPath = path.join(__dirname, 'output', `intermediate-${algorithm}.gif`)
    // create a write stream for GIF data
    const writeStream = createWriteStream(dstPath)
    // when stream closes GIF is created so resolve promise
    writeStream.on('close', () => {
      resolve1()
    })

    const encoder = new GIFEncoder(width, height, algorithm)
    // pipe encoder's read stream to our write stream
    encoder.createReadStream().pipe(writeStream)
    encoder.start()
    encoder.setDelay(200)

    const canvas = createCanvas(width, height)
    const ctx = canvas.getContext('2d')

    // draw an image for each file and add frame to encoder
    for (const file of files) {
      await new Promise(resolve3 => {
        const image = new Image()
        image.onload = () => {
          ctx.drawImage(image, 0, 0)
          encoder.addFrame(ctx)
          resolve3()
        }
        image.src = path.join(imagesFolder, file)
      })
    }
  })
}

createGif('neuquant')
createGif('octree')

NeuQuant Algorithm

Octree Algorithm

Algorithms

• NeuQuant tends to perform faster than Octree
• Octree tends to output a smaller file than NeuQuant
• Octree produces a slight banding effect

The example above encodes 20 images measuring 300px x 240px. The output file from NeuQuant is 1172KB and the Octree is less than half of that at 515KB.

Optimizer

The optimizer works by reusing the color palette from the previous image on the current image. This can reduce the overall processing time signifigantly but its best suited for a sequence of similarly colored images. Use the setThreshold method to set a percentage determining how similar the two images must be to trigger the optimizer. The default is 90%. The optimizer is only used if true is passed as the 4th argument to the constructor.

Progress Event

Works if totalFrames is expressed in constructor, otherwise this value will be 0.

encoder.on('progress', percent => {
  // do something with percent value
})