send form data using ajax

<script type="text/javascript">

    function update_photos(id,imgno)
{
    if(imgno == 'image1'){
    var file = document.getElementById("image_file");
    }
    if(imgno == 'image2'){
      var file = document.getElementById("image_file_s");
      }
    if(imgno == 'image3'){
      var file = document.getElementById("image_file_t");
      }
   
   

        /* Create a FormData instance */
        var formData = new FormData();
        /* Add the file */      
        formData.append("test", file.files[0]);
        formData.append("col_id", id);
        formData.append("imgno", imgno);
       
        console.log(file.files[0]);
 
$.ajax({
type: 'POST',
url: "<?php echo base_url().'column/update_photo/' ?>",
async : true,
data:formData,
processData: false,
contentType: false,
     
success: function(msg) {
//alert(msg);
}
});
}
</script>