webp.wasm

webp.wasm is a pure Webassembly / Javascript port of libwebp. The library supports encoding animated WebP.

APIs

Encode

encode

Get encoder encoderVersion.

function encoderVersion(): Promise<string>

Example

const version = await encoderVersion()
console.log(version) // 1.3.2

encodeRGB

Encodes rgb bitmap an returns WebP Uint8Array. The width and height parameters of the bitmap should be provided.

function encodeRGB(rgb: Uint8Array, width: number, height: number, quality?: number): Promise<Nullable<Uint8Array>>

Example

...
const ctx = canvas.getContext('2d')!
const imgData = ctx.getImageData(0, 0, canvas.width, canvas.height)
const buf = new Uint8Array(3 * canvas.width, canvas.height) 
let j = 0
// remove alpha
imgData.data.forEach((pixel, i) => {
  if ((i + 1) % 4 === 0) {
    return
  }
  buf[j] = pixel
  j++
})
const webpData = await encodeRGB(buf, canvas.width, canvas.height)
const blob = new Blob([webpData!], {type: 'image/webp'})
const blobURL = URL.createObjectURL(blob);
// download webp
const a = document.createElement('a')
a.download = '1.webp'
a.href = blobURL
document.body.appendChild(a)
a.click()
a.remove()

encodeRGBA

Encodes rgba bitmap an returns WebP Uint8Array.

function encodeRGBA(rgba: Uint8Array, width: number, height: number, quality?: number): Promise<Nullable<Uint8Array>>

Example

...
const ctx = canvas.getContext('2d')!
const imgData = ctx.getImageData(0, 0, canvas.width, canvas.height)
const webpData = await encodeRGBA(imgData.data, canvas.width, canvas.height)
// download webp
...

encode

A more advanced API is based on the WebPConfig. Only the lossless and quality parameters are supported now !!!. You can generate low-quality webp with this function.

function encodeRGBA(data: Uint8Array, width: number, height: number, hasAlpha: boolean,config: Partial<WebPConfig>): Promise<Nullable<Uint8Array>>

• hasAlpha: boolean

Whether to include alpha chanel.

• WebPConfig.lossless: number

Lossless encoding (0=lossy(default), 1=lossless).

• WebPConfig.quality: number

Between 0 and 100. Default value is 100.

Example

...
const ctx = canvas.getContext('2d')!
const imgData = ctx.getImageData(0, 0, canvas.width, canvas.height)
const webpData = await encode(imgData.data, canvas.width, canvas.height, true, { lossless: 0 })
// download webp
...

encodeAnimation

Returns animated WebP like GIF.

function encodeAnimation(width: number, height: number, hasAlpha: boolean, frames: WebPAnimationFrame[]): Promise<Nullable<Uint8Array>>

• hasAlpha: boolean

Whether to include alpha chanel.

The WebPAnimationFrame has follow properties:

• WebPAnimationFrame.data: Uint8Array

Frame bitmap.

• WebPAnimationFrame.duration: number

Duration of frame.

Example

...
// record each frame
frames.push({
  data: ctx.getImageData(0, 0, 100, 100).data,
  duration: 20
})
const webpData = await encodeAnimation(100, 100, true, frames)
...
// download webp

Decode

decoderVersion

Get decoder version.

function decoderVersion(): Promise<string>

Example

const version = await decoderVersion()
console.log(version) // 1.3.2

decodeRGB

Decodes webp and outputs WebPDecodedImageData contains rgb bitmap.

function decodeRGB(data: Uint8Array): Promise<Nullable<WebPDecodedImageData>>

Example

...
const fr = new FileReader()
fr.onload = () => {
  if (!fr.result) {
    return
  }
  webpData = fr.result as Uint8Array
  const result = await decodeRGB(webpData)
  // draw imageData
  const ctx = canvas.getContext('2d')!
	ctx.clearRect(0, 0, canvas.width, canvas.height)
	canvas.style.width = `${result.width}px`
	canvas.style.height = `${result.height}px`
	canvas.width = result.width
	canvas.height = result.height
	ctx.putImageData(new ImageData(new Uint8ClampedArray(result.data)), 0, 0)
}
// read webp file
fr.readAsArrayBuffer(file)
...

decodeRGBA

Decodes webp and outputs WebPDecodedImageData contains rgba bitmap.

function decodeRGB(data: Uint8Array): Promise<Nullable<WebPDecodedImageData>>

Example

...
const fr = new FileReader()
fr.onload = () => {
  if (!fr.result) {
    return
  }
  webpData = fr.result as Uint8Array
  const result = await decodeRGBA(webpData)
  // draw imageData
  ...
}
// webp file
fr.readAsArrayBuffer(file)
...

decodeAnimation

Decoding animated WebP image. Returns an array of frames.

function decodeAnimation(data: Uint8Array, hasAlpha: boolean): Promise<Nullable<DecodedWebPAnimationFrame[]>>

Example

...
const fr = new FileReader()
fr.onload = () => {
  if (!fr.result) {
    return
  }
  webpData = fr.result as Uint8Array
  const result = await decodeRGBA(webpData)
  // draw imageData
  ...
}
// webp file
fr.readAsArrayBuffer(file)
...

DecodedWebPAnimationFrame

The object have the following properties:

• DecodedWebPAnimationFrame.width: number

The frame image width.

• DecodedWebPAnimationFrame.height: number

The frame image height.

• DecodedWebPAnimationFrame.duration: number

The frame display duration.

• DecodedWebPAnimationFrame.data: Uint8Array

Raw data in pixels.

WebPDecodedImageData

The object have the following properties:

• WebPDecodedImageData.width: number

The image width in pixels.

• WebPDecodedImageData.height: number

The image height in pixels.

• WebPDecodedImageData.data: Uint8Array

Raw data in pixels.

Note: It has same properties as browser ImageData object, but it is not. There is actually no ImageData in node.

Playing Examples

npm run build-wasm:dev && npm run dev

Building

npm run build