img2sixel.js

/**
 * Example script as cmdline converter.
 * Call: `node img2sixel.js <image files>`
 */


// set to 16 for xterm in VT340 mode
const MAX_PALETTE = 256;

// 0 - default action (background color)
// 1 - keep previous content
// 2 - set background color
const BACKGROUND_SELECT = 0;


const { loadImage, createCanvas } = require('canvas');
const { introducer, FINALIZER, sixelEncode, image2sixel } = require('./lib/index');


async function processImage(filename, palLimit) {
  // load image
  let img;
  try {
    img = await loadImage(filename);
  } catch (e) {
    console.error(`cannot load image "${filename}"`);
    return;
  }
  const canvas = createCanvas(img.width, img.height);
  const ctx = canvas.getContext('2d');
  ctx.drawImage(img, 0, 0);

  // use image2sixel with internal quantizer
  const data = ctx.getImageData(0, 0, img.width, img.height).data;
  console.log(`${filename}:`);
  console.log(image2sixel(data, img.width, img.height, palLimit, BACKGROUND_SELECT));

  // alternatively use custom quantizer library
  // const RgbQuant = require('rgbquant');
  // const q = new RgbQuant({colors: palLimit, dithKern: 'FloydSteinberg', dithSerp: true});
  // q.sample(canvas);
  // const palette = q.palette(true);
  // const quantizedData = q.reduce(canvas);
  // console.log(`${filename}:`);
  // console.log([
  //   introducer(BACKGROUND_SELECT),
  //   sixelEncode(quantizedData, img.width, img.height, palette),
  //   FINALIZER
  // ].join(''));
}

async function main() {
  let palLimit = MAX_PALETTE;
  for (const arg of process.argv) {
    if (arg.startsWith('-p')) {
      palLimit = parseInt(arg.slice(2));
      process.argv.splice(process.argv.indexOf(arg), 1);
      break;
    }
  }
  for (const filename of process.argv.slice(2)) {
    await processImage(filename, palLimit);
  }
}

main();