image processing js

var fs = require("fs"),
  PNG = require("pngjs").PNG;

fs.createReadStream("./anh/test.png")
  .pipe(
    new PNG({
      filterType: 4,
      inputHasAlpha: false,
    })
  )
  .on("parsed", function () {
    console.log(this.height, this.width, this.data.length)
    const matData = [];
    for (let row = 0; row < this.height; ++row) {
      const rowData = [];
      for (let col = 0; col < this.width; ++col) {
        let idx = (this.width * row + col) << 2;
        rowData.push([ this.data[idx], this.data[idx + 1], this.data[idx + 2] ])
      }
      matData.push(rowData)
    }

    console.log(matData, matData.length, matData[0].length);

    this.pack().pipe(fs.createWriteStream("out.png"));
  });