setting width and height of image in codeigniter php not working

i have a codeigniter website where user can upload multiple images, i want all the images to be of the same size, i have done the following code in controller:

if (isset($_POST['addblog'])) {
    $this->load->library('upload');
    $image = array();
    $ImageCount = count($_FILES['image_name']['name']);

    for ($i = 0; $i < $ImageCount; $i++) {
        $_FILES['file']['name'] = $_FILES['image_name']['name'][$i];
        $_FILES['file']['type'] = $_FILES['image_name']['type'][$i];
        $_FILES['file']['tmp_name'] = $_FILES['image_name']['tmp_name'][$i];
        $_FILES['file']['error'] = $_FILES['image_name']['error'][$i];
        $_FILES['file']['size'] = $_FILES['image_name']['size'][$i];

        $uploadPath = './uploads/blog/';
        $config['upload_path'] = $uploadPath;
        $config['allowed_types'] = 'jpg|jpeg|png|gif';
        $config['width'] = 200;
        $config['height'] = 250;

        $this->load->library('upload', $config);
        $this->upload->initialize($config);

        if ($this->upload->do_upload('file')) {

            $imageData = $this->upload->data();

            $uploadImgData[] = $imageData['file_name'];
        }
    }
    $blogimage = $uploadImgData;
}

as u can see i have set the height and width in config, the images are still uploaded in ther original size, can anyone please tell me what is wrong in here, thanks in advance