JavaScript實現的JPEG流編碼器和解碼器：jpg-stream

jpg-stream是JavaScript實現的JPEG流編碼器和解碼器。它是libjpeg的一個JavaScript直接編譯，使用 Emscripten。支持Node和瀏覽器。

Decoding

This example uses the concat-frames module to collect the output of the JPEG decoder into a single buffer.

var JPEGDecoder = require('jpg-stream/decoder');
var concat = require('concat-frames');

// decode a JPEG file to RGB pixels
fs.createReadStream('in.jpg')
  .pipe(new JPEGDecoder)
  .pipe(concat(function(frames) {
    // frames is an array of frame objects (one for JPEGs)
    // each element has a `pixels` property containing
    // the raw RGB pixel data for that frame, as
    // well as the width, height, etc.
  }));

Encoding

You can encode a JPEG by writing or piping pixel data to a JPEGEncoder stream. You can set the quality option to a number between 1 and 100 to control the size vs quality tradeoff made by the encoder.

The JPEG encoder supports writing data in the RGB, grayscale, or CMYK color spaces. If you need to convert from another unsupported color space, first pipe your data through the color-transform module.

var JPEGEncoder = require('jpg-stream/encoder');
var ColorTransform = require('color-transform');

// convert a PNG to a JPEG
fs.createReadStream('in.png')
  .pipe(new PNGDecoder)
  .pipe(new JPEGEncoder({ quality: 80 }))
  .pipe(fs.createWriteStream('out.jpg'));

// colorspace conversion to convert from RGBA to RGB
fs.createReadStream('rgba.png')
  .pipe(new PNGDecoder)
  .pipe(new ColorTransform('rgb'))
  .pipe(new JPEGEncoder)
  .pipe(fs.createWriteStream('rgb.jpg'));

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