Mike42\Escpos\EscposImage::getRasterFormat PHP Method

    private function getRasterFormat()
    {
        /* Loop through and convert format */
        $widthPixels = $this->getWidth();
        $heightPixels = $this->getHeight();
        $widthBytes = $this->getWidthBytes();
        $heightBytes = $this->getHeightBytes();
        $x = $y = $bit = $byte = $byteVal = 0;
        $data = str_repeat("", $widthBytes * $heightPixels);
        if (strlen($data) == 0) {
            return $data;
        }
        do {
            $byteVal |= (int) $this->imgData[$y * $widthPixels + $x] << 7 - $bit;
            $x++;
            $bit++;
            if ($x >= $widthPixels) {
                $x = 0;
                $y++;
                $bit = 8;
                if ($y >= $heightPixels) {
                    $data[$byte] = chr($byteVal);
                    break;
                }
            }
            if ($bit >= 8) {
                $data[$byte] = chr($byteVal);
                $byteVal = 0;
                $bit = 0;
                $byte++;
            }
        } while (true);
        if (strlen($data) != $this->getWidthBytes() * $this->getHeight()) {
            throw new Exception("Bug in " . __FUNCTION__ . ", wrong number of bytes.");
        }
        return $data;
    }