var WHITE_SMILE = '😠'
  , BLACK_SMILE = '😡'
  , SIZE = 17;
function otsu(histogram, pixelsNumber) {
    var sum = 0
      , sumB = 0
      , wB = 0
      , wF = 0
      , mB
      , mF
      , max = 0
      , between
      , threshold = 0;
    for (var i = 0; i < 256; ++i) {
      wB += histogram[i];
      if (wB == 0)
        continue;
      wF = pixelsNumber - wB;
      if (wF == 0)
        break;
      sumB += i * histogram[i];
      mB = sumB / wB;
      mF = (sum - sumB) / wF;
      between = wB * wF * Math.pow(mB - mF, 2);
      if (between > max) {
        max = between;
        threshold = i;
      }
    }
    return threshold;
}
var img = document.getElementsByTagName('img')[0]
  , cnv = document.createElement('canvas')
  , ctx = cnv.getContext('2d'),
  lines = Array(SIZE)
  ;
img.width = img.height = SIZE;
cnv.width = img.width;
cnv.height = img.height;
ctx.drawImage(imgCopy, 0, 0);
var imData = ctx.getImageData(0, 0, cnv.width, cnv.height)
  , histogram = Array(256)
  , i
  , j
  , k
  , red
  , green
  , blue
  , gray;
for (i = 0; i < 256; ++i)
    histogram[i] = 0;
for (i = 0; i < imData.data.length; i += 4) {
  red = imData.data[i];
  blue = imData.data[i + 1];
  green = imData.data[i + 2];
  // alpha = imData.data[i + 3];
  // https://en.wikipedia.org/wiki/Grayscale
  gray = red * .2126 + green * .07152 + blue * .0722;
  histogram[Math.round(gray)] += 1;
}
var threshold = otsu(histogram, imData.data.length / 4);
console.log("threshold = %s", threshold);
for (i = 0; i < imData.height; ++i) {
  lines[i] = "";
  for (j = imData.height * i * 4, k = j + imData.width * 4; ++j) {
    lines[i] += imData.data[i] > threshold ? WHITE_SMILE : BLACK_SMILE;
  }
}

console.log(lines.join('\n'));

/*
😠😠😠😠😠😠😠😠😡😠😠😠😠😠😠😠😠
😠😠😠😠😠😠😠😡😡😡😠😠😠😠😠😠😠
😠😠😠😠😠😠😡😡😡😡😠😠😠😠😠😠😠
😠😠😠😠😠😡😡😡😡😠😠😠😠😠😠😠😠
😠😠😠😠😡😡😡😡😠😠😠😡😡😠😠😠😠
😠😠😠😠😡😡😡😠😠😠😡😡😡😡😠😠😠
😠😠😠😠😠😡😡😡😠😡😡😡😡😡😡😠😠
😠😡😠😠😠😠😡😡😡😡😡😠😡😡😡😡😠
😡😡😡😠😠😠😠😡😡😡😠😠😠😡😡😡😡
😠😡😡😡😠😠😡😡😡😡😡😠😠😠😡😡😠
😠😠😡😡😡😡😡😡😠😡😡😡😠😠😠😠😠
😠😠😠😡😡😡😡😠😠😠😡😡😡😠😠😠😠
😠😠😠😠😡😡😠😠😠😡😡😡😡😠😠😠😠
😠😠😠😠😠😠😠😠😡😡😡😡😠😠😠😠😠
😠😠😠😠😠😠😠😡😡😡😡😠😠😠😠😠😠
😠😠😠😠😠😠😠😡😡😡😠😠😠😠😠😠😠
😠😠😠😠😠😠😠😠😡😠😠😠😠😠😠😠😠
*/