Auto-rotate images locally in the browser by parsing exif data

js-exif-rotate.html

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<input id="file" type="file" accept="image/*" />
<br/>

<h2>As read:</h2>
<img id="placeholder1" width=300/><br/>
<h2>Rotated by exif data:</h2>
<img id="placeholder2" width=300/>

<script>
// Exif orientation value to css transform mapping
// Does not include flipped orientations
var rotation = {
  1: 'rotate(0deg)',
  3: 'rotate(180deg)',
  6: 'rotate(90deg)',
  8: 'rotate(270deg)'
};

function _arrayBufferToBase64( buffer ) {
  var binary = ''
  var bytes = new Uint8Array( buffer )
  var len = bytes.byteLength;
  for (var i = 0; i < len; i++) {
    binary += String.fromCharCode( bytes[ i ] )
  }
  return window.btoa( binary );
}

var orientation = function(file, callback) {

  var fileReader = new FileReader();
  fileReader.onloadend = function() {
    var base64img = "data:"+file.type+";base64," + _arrayBufferToBase64(fileReader.result);
    var scanner = new DataView(fileReader.result);
    var idx = 0;
    var value = 1; // Non-rotated is the default
    if(fileReader.result.length < 2 || scanner.getUint16(idx) != 0xFFD8) {
      // Not a JPEG
      if(callback) {
        callback(base64img, value);
      }
      return;
    }
    idx += 2;
    var maxBytes = scanner.byteLength;
    while(idx < maxBytes - 2) {
      var uint16 = scanner.getUint16(idx);
      idx += 2;
      switch(uint16) {
        case 0xFFE1: // Start of EXIF
          var exifLength = scanner.getUint16(idx);
          maxBytes = exifLength - idx;
          idx += 2;
          break;
        case 0x0112: // Orientation tag
          // Read the value, its 6 bytes further out
          // See page 102 at the following URL
          // http://www.kodak.com/global/plugins/acrobat/en/service/digCam/exifStandard2.pdf
          value = scanner.getUint16(idx + 6, false);
          maxBytes = 0; // Stop scanning
          break;
      }
    }
    if(callback) {
      callback(base64img, value);
    }
  }
  fileReader.readAsArrayBuffer(file);
};

$(function() {

  $('#file').change(function() {
    var file = $(this)[0].files[0];
    if(file) {
      orientation(file, function(base64img, value) {
        $('#placeholder1').attr('src', base64img);
        console.log(rotation[value]);
        var rotated = $('#placeholder2').attr('src', base64img);
        if(value) {
          rotated.css('transform', rotation[value]);
        }
      });
    }
  });
});
</script>

There is another issue in line 53 of the original implementation:

          maxBytes = exifLength - idx;

maxBytes is relative to the whole file and idx is the offset within this file, where we detected the beginning of the EXIF header. We need to add the exifLength to the current offset to get the proper end:

          maxBytes = exifLength + idx;

@tamihelcich / @nicolassaad Any chance you still have the images you were trying so I can test if this fixes the issue? 🙂

Thanks a lot for this gist @runeb and for the fixes @kedrovski! I used both as the base for a new, class-based version.

Improvements:

• Replaced the callback with async/await
• Handles all 8 possible orientations
• Made the base64 part optional (it might not be needed for everyone—I didn't need it).
• Can return the raw orientation value (1–8)
• Replaced the loop with a functional programming-based solution
• I broke up the code to smaller methods to make it a bit more documented and easier to modify.

Here you go, I hope someone finds it useful: https://gist.github.com/vdavid/3f9b66b60f52204317a4cc0e77097913