public function crop($width, $height, $mode = 'tl')
    {
        if ( !is_numeric($width) ) {
            throw new \InvalidArgumentException('$width must be numeric');
        }

        if ( !is_numeric($height) ) {
            throw new \InvalidArgumentException('$height must be numeric');
        }

        if ( $this->newImage )
        {
            $this->sourceImage = $this->newImage;
        }

        $oldWidth   = ($this->newImage) ? imagesx($this->newImage) : $this->source['width'];
        $oldHeight  = ($this->newImage) ? imagesy($this->newImage) : $this->source['height'];

        $this->create($width, $height);

        $startX     = $startY = 0;
        $cropWidth  = $sourceWidth  = $width;
        $cropHeight = $sourceHeight = $height;

        if ( is_array($mode) )
        {
            $startX = $mode[0];
            $startY = $mode[1];
        }

        if ($mode === self::CROP_TOP_CENTER)
        {
            $startX = ($oldWidth - $cropWidth) / 2;
        }
        else if ($mode === self::CROP_TOP_RIGHT)
        {
            $startX = $oldWidth - $cropWidth;
        }
        else if ($mode === self::CROP_CENTER_LEFT)
        {
            $startY = ($oldHeight - $cropHeight) / 2;
        }
        else if ($mode === self::CROP_CENTER_CENTER)
        {
            $startX = ($oldWidth - $cropWidth)   / 2;
            $startY = ($oldHeight - $cropHeight) / 2;
        }
        else if ($mode === self::CROP_CENTER_RIGHT)
        {
            $startX = $oldWidth - $cropWidth;
            $startY = ($oldHeight - $cropHeight) / 2;
        }
        else if ($mode === self::CROP_BOTTOM_LEFT)
        {
            $startY = $oldHeight - $cropHeight;
        }
        else if ($mode === self::CROP_BOTTOM_CENTER)
        {
            $startX = ($oldWidth - $cropWidth)   / 2;
            $startY = $oldHeight - $cropHeight;
        }
        else if ($mode === self::CROP_BOTTOM_RIGHT)
        {
            $startX = $oldWidth - $cropWidth;
            $startY = $oldHeight - $cropHeight;
        }
        else
        {
        }

        imagecopyresampled(
            $this->newImage,
            $this->sourceImage,
            0, 0, $startX, $startY,
            $cropWidth, $cropHeight, $sourceWidth, $sourceHeight);

        return $this;
    }