title: Fabric.js canvas.toDataURL() sent to PHP by Ajax
body: <p>I have a problem here when I need create a image with transparent background. I still don´t know if the problem is with fabricjs or with php. Everything works fine when I sent a image with colored background. The problem occurs when I send a image with transparent background.
  The generated image is created with black background.
  So, let me explain better:
  When the user click in save button, I´m sending the string representation of the canvas to php in the server-side, to be generated the image of the canvas. So I´m using the follow function to sending the string representation of the canvas by Ajax (POST function of jQuery):</p>
  
  <pre>
  
      function sendStringRepresentation(){
          var strDataURI = canvas.toDataURL();
          strDataURI = strDataURI.substr(22, strDataURI.length);
  
          $.post("action/createImage.php",
          { 
              str: strDataURI
          },
          function(data){
              if(data == "OK"){
                  $("#msg").html("Image created.");
          }
          else{
              $("#msg").html("Image not created.");
              }
          });
      }
  
  </pre>
  
  <p>In PHP file I´m using the follow code to generate the image:</p>
  
  <pre>
  
      // createImage.php
  
      $data = base64_decode($_POST["str"]);
  
      $urlUploadImages = "../uploads/img/";
      $nameImage = "test.png";
  
      $img = imagecreatefromstring($data);
  
      if($img) {
          imagepng($img, $urlUploadImages.$nameImage, 0);
          imagedestroy($img);
  
          // [database code]
  
          echo "OK";
      }
      else {
          echo 'ERROR';
      }
  
  </pre>
  
  <p>Again, the problem is just with background transparent canvas. With colored background everything works fine.</p>