Using raw image data from ajax request for data URI

Solution 1:

Thanks for that. I've done a bit more digging on this and it turns out there is a solution at least on current versions of Firefox and Chrome (EDIT: IE10 works too). You can use XMLHttpRequest2 and use a typed array (Uint8Array). The following code works:

<!DOCTYPE html>
<html>
<head>
<script type='text/javascript'>

function init()
{
    var xmlHTTP = new XMLHttpRequest();
    xmlHTTP.open('GET','/images/photos/badger.jpg',true);

    // Must include this line - specifies the response type we want
    xmlHTTP.responseType = 'arraybuffer';

    xmlHTTP.onload = function(e)
    {

        var arr = new Uint8Array(this.response);


        // Convert the int array to a binary string
        // We have to use apply() as we are converting an *array*
        // and String.fromCharCode() takes one or more single values, not
        // an array.
        var raw = String.fromCharCode.apply(null,arr);

        // This works!!!
        var b64=btoa(raw);
        var dataURL="data:image/jpeg;base64,"+b64;
        document.getElementById("image").src = dataURL;
    };

    xmlHTTP.send();
}

</script>
</head>
<body onload='init()'>
<img id="image" alt="data url loaded image" />
</body>
</html>

Basically you ask for a binary response, then create an 8-bit unsigned int view of the data before converting it back into a (binary-friendly) string String.fromCharCode(). The apply is necessary as String.fromCharCode() does not accept an array argument. You then use btoa(), create your data url and it then works.

The following resources were useful for this:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays?redirectlocale=en-US&redirectslug=JavaScript%2FTyped_arrays

and

http://www.html5rocks.com/en/tutorials/file/xhr2/

Nick

Solution 2:

Nick's answer works very well. But when I did this with a fairly large file, I got a stack overflow on

var raw = String.fromCharCode.apply(null,arr);

Generating the raw string in chunks worked well for me.

var raw = '';
var i,j,subArray,chunk = 5000;
for (i=0,j=arr.length; i<j; i+=chunk) {
   subArray = arr.subarray(i,i+chunk);
   raw += String.fromCharCode.apply(null, subArray);
}

Using raw image data from ajax request for data URI

Solution 1:

Solution 2:

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