JuicyPixels-webp

Pure Haskell WebP decoder and encoder for JuicyPixels.

Features

• VP8L Lossless: Full decode and encode support
• VP8 Lossy: Full decode and encode with quality control (0-100)
• Alpha Channels: RGBA support for both lossless and lossy
• Animations: Decode and encode animated WebP files
• All Container Formats: Simple and extended WebP

Installation

stack build

Usage

Decoding

import Codec.Picture.WebP
import qualified Data.ByteString as B

-- Decode a still WebP image
fileData <- B.readFile "image.webp"
case decodeWebP fileData of
  Right (ImageRGB8 img)  -> -- VP8 lossy without alpha
  Right (ImageRGBA8 img) -> -- VP8L lossless or VP8 with alpha
  Left err               -> -- Handle error

For animated images, use decodeWebPFirstFrame for the first frame or decodeWebPAnimation / decodeWebPAnimationComposited for all frames.

Encoding

import Codec.Picture
import Codec.Picture.WebP

-- Lossless encoding (takes Image PixelRGBA8)
let webpData = encodeWebPLossless img
B.writeFile "output.webp" webpData

-- Lossy encoding with quality (0-100, takes Image PixelRGB8)
let webpData = encodeWebPLossy img 80
B.writeFile "output.webp" webpData

-- Lossy with alpha channel (takes Image PixelRGBA8)
let webpData = encodeWebPLossyWithAlpha img 80
B.writeFile "output.webp" webpData

Animations

-- Decode animation frames
case decodeWebPAnimation fileData of
  Right frames -> mapM_ processFrame frames
  Left err     -> handleError err

-- Encode animation
let frames = [WebPEncodeFrame img1 100 0 0, WebPEncodeFrame img2 100 0 0]
let webpData = encodeWebPAnimation frames canvasWidth canvasHeight quality

Animation frame offsets must be nonnegative and even, and each frame must fit within the canvas. Durations are milliseconds in 0..16777215. Canvas dimensions must be in 1..16777216, with at most 4294967295 pixels; VP8 frame dimensions must be in 1..16383. Invalid parameters raise an error. VP8 encoding also raises an error if its first partition exceeds the format's 524287-byte limit.

Testing

stack test

API

Decoding

• decodeWebP :: ByteString -> Either String DynamicImage
• decodeWebPFirstFrame :: ByteString -> Either String DynamicImage
• decodeWebPAnimation :: ByteString -> Either String [WebPAnimFrame]
• decodeWebPAnimationComposited :: ByteString -> Either String [Image PixelRGBA8]

Encoding

• encodeWebPLossless :: Image PixelRGBA8 -> ByteString
• encodeWebPLossy :: Image PixelRGB8 -> Int -> ByteString
• encodeWebPLossyWithAlpha :: Image PixelRGBA8 -> Int -> ByteString
• encodeWebPAnimation :: [WebPEncodeFrame] -> Int -> Int -> Int -> ByteString

Documentation

• docs/webp-format.md - VP8L lossless specification
• docs/vp8-bitstream.md - VP8 lossy specification
• STATUS.md - Current implementation status
• PLAN.md - Original implementation plan (historical)

License

BSD-3-Clause