显示 PNG 图像作为对 jQuery AJAX 请求的响应

Question

Is it possible to display an image returned by jQuery AJAX call, in the main stream of your HTML?

I have a script that draws an image with a header (image/PNG). When I simply call it in the browser, the image is displayed.

But when I make an AJAX call with jQuery on this script, I can't display a clean image, I have something with a lot of strange symbols. This is my script that makes the image with a header (image/PNG).

#!/usr/bin/perl 

use strict;
use CGI;
use Template;
use CGI::Carp qw(fatalsToBrowser);
use lib qw(lib);
use GD;

my $cgi    = new CGI;

my $id_projet            =  $cgi   -> param('id_projet') ;      # 

# Create a new image
my $image = new GD::Image(985,60) || die;
my $red =  $image->colorAllocate(255, 0, 0);
my $black =  $image->colorAllocate(0, 0, 0);

$image->rectangle(0,0,984,59,$black);
$image->string(gdSmallFont,2,10,"Hello $id_projet ",$black);
# Output the image to the browser

print $cgi -> header({-type => 'image/png',-expires => '1d'});

#binmode STDOUT;

print $image->png;

Then I have my main script with an AJAX call inside:

  <script type="text/javascript" > 

  $(document).ready( function() { 

  $.ajax({
  type: "POST",
  url:'get_image_probes_via_ajax.pl',
  contentType: "image/png",
  data: "id_projet=[% visual.projet.id %]",
  success: function(data){
  $('.div_imagetranscrits').html('<img src="' + data + '" />'); },
 } );

 </script>  

In my HTML file I have one div with class="div_imagetranscrits" to be filled with my image.

I don't see what I'm doing wrong. The other solution is to make my script write the image on disk and just get the path to include in the src to display it. But I was thinking it was possible to get the image with an image/PNG header directly from an AJAX request.

Answer 1

You'll need to send the image back base64 encoded, look at this: http://php.net/manual/en/function.base64-encode.php

Then in your ajax call change the success function to this:

$('.div_imagetranscrits').html('<img src="data:image/png;base64,' + data + '" />');

Answer 2

Method 1

You should not make an ajax call, just put the src of the img element as the url of the image.

This would be useful if you use GET instead of POST

<script type="text/javascript" > 

  $(document).ready( function() { 
      $('.div_imagetranscrits').html('<img src="get_image_probes_via_ajax.pl?id_project=xxx" />')
  } );

</script>

---

Method 2

If you want to POST to that image and do it the way you do (trying to parse the contents of the image on the client side, you could try something like this: http://en.wikipedia.org/wiki/Data_URI_scheme

You'll need to encode the data to base64, then you could put data:[<MIME-type>][;charset=<encoding>][;base64],<data> into the img src

as example:

<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==" alt="Red dot img" />

To encode to base64:

• in plain javascript, see How can you encode a string to Base64 in JavaScript?
• in perl http://perldoc.perl.org/MIME/Base64.html
• in php http://php.net/manual/en/function.base64-encode.php

Answer 3

This allows you to just get the image data and set to the img src, which is cool.

var oReq = new XMLHttpRequest();
oReq.open("post", '/somelocation/getmypic', true );        
oReq.responseType = "blob";
oReq.onload = function ( oEvent )
{
    var blob = oReq.response;
    var imgSrc = URL.createObjectURL( blob );                        
    var $img = $( '<img/>', {                
        "alt": "test image",
        "src": imgSrc
    } ).appendTo( $( '#bb_theImageContainer' ) );
    window.URL.revokeObjectURL( imgSrc );
};
oReq.send( null );

The basic idea is that the data is returned untampered with, it is placed in a blob and then a url is created to that object in memory. See here and here . Note supported browsers.

Answer 4

Thanks to above answers and after some more searching able to come up with below solution for Spring Boot application.

HTML

<div class="row">
     <div class="col-11" id='img_div'>
     </div>
</div>

Javascript

function loadImage() {

        $.ajax({
            type: "GET",
            url: contextPath+"/loadImage",
            data: null,
            dataType: 'text',
            cache: false,
            timeout: 600000,
            success: function (data) {
                $('#img_div').html('<img id="img" src="data:image/png;base64,' + data + '" />');
                
            },
            error: function (e) {
                //handle error
            }
        });
    
    }

Controller Method

@GetMapping("/loadImage")
@ResponseBody
private String loadImagefromExternalFolder(HttpServletRequest request){     
    String encodedString = "";
    
    try {       
        RandomAccessFile f =  new RandomAccessFile("C:\\your_folder_path\\your_img.PNG", "r");
        byte[] b = new byte[(int)f.length()];
        f.readFully(b);
        
        encodedString = Base64.getEncoder().encodeToString(b);

    }catch (Exception e) {
        // handle error
    }


    return encodedString;
    
}

Answer 5

Update for 2022: Use blobs -- you no longer need to waste time and bandwidth converting to base64.

Here is the example from https://developer.mozilla.org/en-US/docs/Web/API/Response#fetching_an_image

const image = document.querySelector('.my-image');
fetch('flowers.jpg')
.then(response => response.blob())
.then(blob => {
  const objectURL = URL.createObjectURL(blob);
  image.src = objectURL;
});