canvacard/libs/Threshold.js

Powerful image manipulation package for beginners.

const Canvas = require("@napi-rs/canvas");

module.exports = async (img, amount = 50) => {
  const image = await Canvas.loadImage(img);
  const canvas = await Canvas.createCanvas(image.width, image.height);
  const ctx = canvas.getContext("2d");
  ctx.drawImage(image, 0, 0);

  const imgData = ctx.getImageData(0, 0, canvas.width, canvas.height);

  for (let i = 0; i < imgData.data.length; i += 4) {
    var r = imgData.data[i];
    var g = imgData.data[i + 1];
    var b = imgData.data[i + 2];
    var v = (0.2126 * r + 0.7152 * g + 0.0722 * b >= amount) ? 255 : 0;
    imgData.data[i] = imgData.data[i + 1] = imgData.data[i + 2] = v
  }

  ctx.putImageData(imgData, 0, 0);

  return canvas.toBuffer("image/png");
};