lzw = function lzw(minCodeSize, data, pixelCount) {
  var MAX_STACK_SIZE = 4096;
  var nullCode = -1;
  var npix = pixelCount;
  var available, clear, code_mask, code_size, end_of_information, in_code, old_code, bits, code, i, datum, data_size, first, top, bi, pi;
  var dstPixels = new Array(pixelCount);
  var prefix = new Array(MAX_STACK_SIZE);
  var suffix = new Array(MAX_STACK_SIZE);
  var pixelStack = new Array(MAX_STACK_SIZE + 1); // Initialize GIF data stream decoder.

  data_size = minCodeSize;
  clear = 1 << data_size;
  end_of_information = clear + 1;
  available = clear + 2;
  old_code = nullCode;
  code_size = data_size + 1;
  code_mask = (1 << code_size) - 1;

  for (code = 0; code < clear; code++) {
    prefix[code] = 0;
    suffix[code] = code;
  } // Decode GIF pixel stream.


  var datum, bits, count, first, top, pi, bi;
  datum = bits = count = first = top = pi = bi = 0;

  for (i = 0; i < npix;) {
    if (top === 0) {
      if (bits < code_size) {
        // get the next byte
        datum += data[bi] << bits;
        bits += 8;
        bi++;
        continue;
      } // Get the next code.


      code = datum & code_mask;
      datum >>= code_size;
      bits -= code_size; // Interpret the code

      if (code > available || code == end_of_information) {
        break;
      }

      if (code == clear) {
        // Reset decoder.
        code_size = data_size + 1;
        code_mask = (1 << code_size) - 1;
        available = clear + 2;
        old_code = nullCode;
        continue;
      }

      if (old_code == nullCode) {
        pixelStack[top++] = suffix[code];
        old_code = code;
        first = code;
        continue;
      }

      in_code = code;

      if (code == available) {
        pixelStack[top++] = first;
        code = old_code;
      }

      while (code > clear) {
        pixelStack[top++] = suffix[code];
        code = prefix[code];
      }

      first = suffix[code] & 0xff;
      pixelStack[top++] = first; // add a new string to the table, but only if space is available
      // if not, just continue with current table until a clear code is found
      // (deferred clear code implementation as per GIF spec)

      if (available < MAX_STACK_SIZE) {
        prefix[available] = old_code;
        suffix[available] = first;
        available++;

        if ((available & code_mask) === 0 && available < MAX_STACK_SIZE) {
          code_size++;
          code_mask += available;
        }
      }

      old_code = in_code;
    } // Pop a pixel off the pixel stack.


    top--;
    dstPixels[pi++] = pixelStack[top];
    i++;
  }

  for (i = pi; i < npix; i++) {
    dstPixels[i] = 0; // clear missing pixels
  }

  return dstPixels;
}
javascript port of java LZW decompression
Original java author url: https://gist.github.com/devunwired/4479231