var pixelr = require('pixelr')
  , colors = require('./node_modules/blessed/lib/colors');
// Colors.js contains a function to match RGB colors to terminal characters.
// It's from the awesome library Blessed: https://github.com/chjj/blessed

/** pixelr.read(filename, format, callback)
 * Format can be either 'jpeg' or 'png'.
 * This function creates a one-dimensional array of values.
 * PNGs have 4 values per pixel: R, G, B, Alpha
 * JPEGs have 3 values per pixel: R, G, B
 * The callback takes an object with properties 'pixels' (an array), 'width', and 'height'.
 */
pixelr.read("image.jpeg", "jpeg", asciizeImage);

function asciizeImage(err, image) {
  if (err) { console.log(err); return; }
  return asciize(image, 400, 400);
}

function asciize(image, asciiWidth, asciiHeight) {
  var countedColors = countColors(image, asciiWidth, asciiHeight)
    , ascii = ''
    , ansiColorCode
    , previousColor = -2;

  for (var i = 0; i < countedColors.length; i++) {
    ansiColorCode = sortColors(countedColors[i])[0].color;
    if (ansiColorCode !== previousColor) {
      ascii += '\033[38;5;' + ansiColorCode + 'm';
      previousColor = ansiColorCode;
    }
    ascii += '#';
  }

  return ascii + '\033[0m';
}

function sortColors(countedColors) {
  var sortedColors = []
    , color;

  for (color in countedColors) {
    sortedColors.push({'color': color, 'count': countedColors[color]});
  }
  return sortedColors.sort(s);

  function s(a, b) {
    if (a.count < b.count) {
      return 1;
    } else if (a.count > b.count) {
      return -1;
    }
    return 0;
  }
}

function countColors(image, asciiWidth, asciiHeight) {
  var colorCount = []
    , blockWidth  = image.width / asciiWidth
    , blockHeight = image.height / asciiHeight
    , index = 0
    , pixelIndex
    , pixelColor;

  for (var i = 0; i < image.pixels.length; i += 3) {
    pixelIndex = i / 3;
    index = Math.floor(pixelIndex / blockWidth) % asciiWidth + 
            Math.floor(pixelIndex / image.width / blockHeight) * asciiWidth;
    if (!colorCount[index]) {
      colorCount[index] = {};
    }
    pixelColor = colors.match(image.pixels[i], image.pixels[i + 1], image.pixels[i + 2]);
    if (!(pixelColor in colorCount[index])) {
      colorCount[index][pixelColor] = 0;
    }
    // Assign less weight to grayscale values for a more interesting picture
    if (pixelColor >= 232 || pixelColor === 59) {
      colorCount[index][pixelColor] += .5;
    } else {
      colorCount[index][pixelColor]++;
    }
  }

  return colorCount;
}

$ npm install pixelr