จะให้ Ajax ส่งค่า enctype="multipart/form-data ยังไงครับพอดีติดปัญหาอ่ะครับ

<div id="myModal" class="modal fade" aria-labelledby="myModalLabel" aria-hidden="true" tabindex="-1" role="dialog">
  <div class="modal-dialog">
    <div class="modal-content">
      <form method="post" action="<?php echo base_url('admin/Categories/add_category_validation');?>" enctype="multipart/form-data">
        <div class="modal-header">
          <h5 class="modal-title">เพิ่มหมวดอสังหาฯ</h5>
          <button type="button" class="close" data-dismiss="modal" aria-hidden="true" onClick="window.location.reload()">×</button>
        </div>
        <div class="modal-body" id="myModalBody">
          <div id="alert-msg"></div>
          <div class="form-group">
            <label for="name">Category</label>
            <input class="form-control" id="name" name="name" type="text" value="" />
          </div>
          <div class="control-group">
            <label for="exampleSelect1">Parent</label>
            <div class="controls">
              <select id="sub_category" class="form-control" name="sub_category">
                <option></option>
                <option value="0">Top Level Category</option>
                <?php foreach ($categories as $cat): ?>
                <option value="<?php echo $cat['id']; ?>"><?php echo $cat['name']; ?></option>
                <?php endforeach; ?>
              </select>
            </div>
          </div>
          <div class="form-group">
            <label for="exampleTextarea">Description</label>
            <textarea class="form-control" id="textarea" name="textarea" rows="3"></textarea>
          </div>
          <div class="form-group">
            <label for="exampleInputFile">Logo Category</label>
            <input type="file" class="form-control-file" name="image_file" id="image_file">
            <small id="fileHelp" class="form-text text-muted">This is some placeholder block-level help text for the above input. It's a bit lighter and easily wraps to a new line.</small> </div>
        </div>
        <div class="modal-footer">
          <input class="btn btn-default" id="submit" name="submit" type="button" value="Send Mail" />
          &nbsp;
          <button type="button" class="btn btn-danger float-left"  data-dismiss="modal" onClick="window.location.reload()" />
          Close
          </button>
        </div>
      </form>
    </div>
  </div>
</div>


<!--load jquery & bootstrap js files--> 
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> 
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script> 


<script type="text/javascript">
$('#submit').click(function() {
    var form_data = {
        name: $('#name').val(),
        sub_category: $('#sub_category').val(),
        textarea: $('#textarea').val(),
		image_file: $('#image_file').val()
	};
	 $.ajax({
        url: "<?php echo site_url('admin/Categories/add_category_validation'); ?>",
        type: 'POST',
        data: form_data,
	 success: function(msg) {
            if (msg == 'YES')
                $('#alert-msg').html('<div class="alert alert-success text-center">Your mail has been sent successfully!</div>');
            else if (msg == 'NO')
                $('#alert-msg').html('<div class="alert alert-danger text-center">Error in sending your message! Please try again later.</div>');
            else
                $('#alert-msg').html('<div class="alert alert-danger">' + msg + '</div>');
        }
    });
    return false;
});
</script>

<?php  

defined('BASEPATH') OR exit('No direct script access allowed');

class Categories extends CI_Controller
{
    var $session_user;
    function __construct() 
	{
		parent::__construct();
		$this->session_user = $this->session->userdata('logged_in');
		$this->load->library('facebook');
		$this->load->library('googleplus');
		$this->load->model('admin/Category_admin');
		$this->load->library('form_validation');
		
    }
/*------------------------------------------------------------------------------------------------------------------------------------*/	
	
public function index()
{
	if ($this->session->userdata('logged_in'))
	{
		$login = $this->session->userdata('logged_in');
		
		if($login['type_user']=='administrator')
		{
			$data['categories'] = $this->Category_admin->category_get_all();
			$data['title'] = 'Categories';
		    $data['session_user'] = $this->session_user;	
	  	    
			$this->load->view('templates/header_administrator',$data);
	        $this->load->view('admin/categories',$data);
			$this->load->view('templates/footer_administrator');
			$this->load->view('admin/modal_category');
		}
		else
		{
			redirect(base_url('index'));
            exit;	
		}
	}
	else
	{
		redirect(base_url('index'));
        exit;
    }
}
/*------------------------------------------------------------------------------------------------------------------------------------*/

public function add_category_validation()
{
	$this->form_validation->set_rules('name','User Name','required');
	$this->form_validation->set_rules('sub_category','sub_category','required');
	$this->form_validation->set_rules('textarea','textarea','required');

   if($this->form_validation->run()==FALSE)
	{
		echo $this->upload->display_errors();  
		
	}else{

	if(isset($_FILES["image_file"]))
	{
		$config['upload_path'] = './upload/';  
        $config['allowed_types'] = 'jpg|jpeg|png|gif';
		$config['file_name'] = date("dmYHis");   

        $this->load->library('upload', $config);  
		$this->upload->do_upload('image_file');
		
		$data = $this->upload->data();  
			
        $config['image_library'] = 'gd2';  
        $config['source_image'] = './upload/'.$data["file_name"];  
        $config['create_thumb'] = FALSE;  
        $config['maintain_ratio'] = TRUE;  
        $config['quality'] = '80%';  
        $config['width'] = 200;  
        $config['height'] = 200;  
        $config['new_image'] = './upload/'.$data["file_name"];  
			
			
        $this->load->library('image_lib', $config);  
        $this->image_lib->resize();  
        $this->load->model('admin/Category_admin');  
			
        $image_data = array(  
        'img'=>$data["file_name"]  
        );
			
			
		$image_data['parent_id'] = $this->input->post('sub_category');
		$image_data['name']= $this->input->post('name');
		$image_data['detail'] = $this->input->post('textarea');
		$image_data['publish'] = 'Yes';
		$image_data['date_added'] = date("Y-m-d H:i:s");
		$image_data['date_edit'] = date("Y-m-d H:i:s");
			
		$this->Category_admin->insert_image($image_data);  
		echo "YES";
    }
	
	
}
}

/*------------------------------------------------------------------------------------------------------------------------------------*/

}

function readURL(input) {
    var rs;
    if (input.files && input.files[0]) {
        var reader = new FileReader();
        reader.onload = function (e) {
		rs=e.target.result;
        }
        reader.readAsDataURL(input.files[0]);
        return rs;
    } return false;
}

<script type="text/javascript">
function b64Decode(str) {
    return decodeURIComponent(Array.prototype.map.call(atob(str), function(c) {
        return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
    }).join(''));
}
function readURL(input) {
    if (input.files && input.files[0]) {
        var reader = new FileReader();
        reader.onload = function (e) {
			$('#preview').attr('src', e.target.result);
        }
        reader.readAsDataURL(input.files[0]);
    }
}
$(document).ready(function(e) {
	$('li.first>a:eq(0)').data('ci-pagination-page',0);
<?php if(isset($inc_js)) include $inc_js;?>
	$('#fileup').change(function(e) {
		readURL(this); $('#upload').show() 
	}); 
	$('#upload').click(function(e){
		//alert(src.substr(0,50)); // data:image/png;base64,
		var src=$('#preview').attr('src');
		$.ajax({
			url: "<?=(isset($upload_prog)? $upload_prog : '/Administrator/upload/')?>",
			type:'POST', 		
			data:{
				img: src.replace(/data:image\/(png|jpeg|jpg|bmp|gif);base64,/, ''),
				ext: src.replace(/^data:image\/(png|jpeg|jpg|bmp|gif);base64,.+/, '$1'),
				filename: filename
			}
		}).done(function(msg){
			eval('var rs = '+msg);
			if(rs.msg=='complete') $('#img_url').val(rs.data.fn);
			$('#upload').hide();
		});
	});
}).delegate('.hk_input','focusout', function(e){
	if( $(e.target).is(':invalid') ){
		show_invalid(e.target)
	} else {
		$(e.target).removeClass('hk_invalid');
	}
}).delegate('.hk_input','keyup', function(e){
	var et=$(e.target);
	et.attr('title', (et.attr('placeholder')!=null?et.attr('placeholder') : 'Please fill in this box'));
});
function show_invalid(ob){
	var et=$(ob), mm='', vl=et.val(); et.addClass('hk_invalid'); 
	var nm = et.data('name')!=null? et.data('name') : 
		(et.attr('placeholder')!=null?et.attr('placeholder') : et.attr('name')), 
	ermsg = et.data('errmsg'), mn=parseInt('0'+et.data('min')), mx=parseInt('0'+et.data('max'));
	if( ermsg && ermsg.length>0 ) mm=ermsg;
	else if(mn>0 && vl.length==0) mm="This field cannot be left blank";
	else if(mn>vl.length) mm='This field is less than '+mn+' characters';
	else if(mx>0 && mx<vl.length) mm='This field is longer than '+mx+' characters';
	else mm="This field is Wrong Format";
	$(et).attr('title', mm);
}
function hk_validate(){
	$('.hk_input').each(function(idx, ele){
		if( $(ele).is(':invalid') ){
			$(ele).addClass('hk_invalid'); 
		} else {
			$(ele).removeClass('hk_invalid');
		}
	})
	return $('.hk_invalid').length==0;
}
String.prototype.shuffle = function () {
    var a = this.split(""),
        n = a.length;

    for(var i = n - 1; i > 0; i--) {
        var j = Math.floor(Math.random() * (i + 1));
        var tmp = a[i];
        a[i] = a[j];
        a[j] = tmp;
    }
    return a.join("");
};
</script>

<div class="col-xs-6">
	<div class="form-group">
		<label>Avatar</label>
		<img src="/asset/avatar/<?=$avatar?>" alt="" id="preview" width="120" />&nbsp;&nbsp;
		<input type="file" id=fileup style="display: none;" >&nbsp;&nbsp;
		<button type="button" id=UploadBT class="btn-info"  onClick="$('#fileup').click()" >เลือกไฟล์</button><br>
	</div>
	<div class="form-group">
		<label>ฃื่อ-นามสกุล <b style="color: red">***</b></label>
		<input type="text" id=iName class="form-control input-sm hk_input" value="{name}" required placeholder="ฃื่อ-นามสกุล" ><br>
		<label>บัตรประชาชน <b style="color: red">***</b></label>
		<input type="text" id=iC_id class="form-control input-sm hk_input" value="{c_id}" required pattern="[0-9]{13}" placeholder="หมายเลขบัตรประชาชน" ><br>
		<label>โทรศัพท์ <b style="color: red">***</b></label>
		<input type="text" id=iPhone class="form-control input-sm hk_input" value="{phone}" required pattern="[0-9\s\-,]{10,50}" placeholder="หมายเลขโทรศัพท์" ><br>
		<label>อีเมล</label>
		<input type="email" id=iEmail class="form-control input-sm hk_email" value="{email}"  placeholder="ที่อยู่อีเมล" >
	</div>
</div>

<?php
if ($_POST) {
    if (isset($_FILES['image'])) {
        move_uploaded_file($_FILES['image']['tmp_name'], __DIR__ . '/'. $_FILES['image']['name']);
    }

    $output = [];
    $output['input_post'] = $_POST;
    $output['input_file'] = $_FILES;
    echo json_encode($output);
    exit;
}
?>
<!doctype html>
<html class="no-js" lang="">
    <head>
        <meta charset="utf-8">
        <meta http-equiv="x-ua-compatible" content="ie=edge">
        <title></title>
    </head>
    <body>
        <h1>Test ajax upload</h1>
        <form id="testform" method="post" action="test.php" enctype="multipart/form-data">
            Name: <input type="text" name="name" value=""><br>
            File: <input type="file" name="image"><br>
            <button type="submit">Submit</button>
        </form>
        <div class="form-result-placeholder"></div>
    
    
        <script src="https://code.jquery.com/jquery-3.2.1.min.js" integrity="sha256-hwg4gsxgFZhOsEEamdOYGBf13FyQuiTwlAQgxVSNgt4=" crossorigin="anonymous"></script>
        <script>
            $('#testform').on('submit', function(e) {
                e.preventDefault();
                
                var formUrl = $(this).attr('action');
                var formObj = $(this)[0];
                var formData = new FormData(formObj);

                $.ajax({
                    url: formUrl,
                    data: formData,
                    method: 'POST',
                    contentType: false,
                    processData: false,
                })
                .done(function(response) {
                    console.log(response);
                });
            });
        </script>
    </body>
</html>

function readURL(input) {
	var b64=;
	if (input.files && input.files[0]) {
        	var reader = new FileReader();
	        reader.onload = function (e) {
			b64=e.target.result;
		}
		reader.readAsDataURL(input.files[0]);
		return b64;
	}
	return false;
}
// ข้างล่างส่วนที่เรียกใช้งาน
var src = readURL($('#fileup')); // ตรงนี้จะได้ image ในรูปแบบ base64 มีส่วนหัวแสดงประเภทรูปภาพ
$.ajax({
	url: '.....',
	type:'POST', 		
	data:{
		img: src.replace(/data:image\/(png|jpeg|jpg|bmp|gif);base64,/, ''), // เอาส่วนหัวออกเหลือแต่ข้อมูลรูปภาพ
		ext: src.replace(/^data:image\/(png|jpeg|jpg|bmp|gif);base64,.+/, '$1'), // แสดงประเภทรูปภาพ
	}
}).done(function(msg){
   //
});

var form_data = new FormData(form);
$.ajax({
	url : "URL",
	type: "POST",
	data : form_data,
	contentType: false,
	cache: false,
	processData:false,
	mimeType: "multipart/form-data"
}).done(function(res){
	/*Statement*/
});