Image_GD::_do_resize PHP Method

    protected function _do_resize($width, $height)
    {
        // Presize width and height
        $pre_width = $this->width;
        $pre_height = $this->height;
        // Loads image if not yet loaded
        $this->_load_image();
        // Test if we can do a resize without resampling to speed up the final resize
        if ($width > $this->width / 2 and $height > $this->height / 2) {
            // The maximum reduction is 10% greater than the final size
            $reduction_width = round($width * 1.1);
            $reduction_height = round($height * 1.1);
            while ($pre_width / 2 > $reduction_width and $pre_height / 2 > $reduction_height) {
                // Reduce the size using an O(2n) algorithm, until it reaches the maximum reduction
                $pre_width /= 2;
                $pre_height /= 2;
            }
            // Create the temporary image to copy to
            $image = $this->_create($pre_width, $pre_height);
            if (imagecopyresized($image, $this->_image, 0, 0, 0, 0, $pre_width, $pre_height, $this->width, $this->height)) {
                // Swap the new image for the old one
                imagedestroy($this->_image);
                $this->_image = $image;
            }
        }
        // Create the temporary image to copy to
        $image = $this->_create($width, $height);
        // Execute the resize
        if (imagecopyresampled($image, $this->_image, 0, 0, 0, 0, $width, $height, $pre_width, $pre_height)) {
            // Swap the new image for the old one
            imagedestroy($this->_image);
            $this->_image = $image;
            // Reset the width and height
            $this->width = imagesx($image);
            $this->height = imagesy($image);
        }
    }