HTML/Javascript Access EXIF data before file uploa

问题:

I am trying to extract EXIF data from a image(jpeg) which has been dragged into the browser or has been selected via a html file input element.

I managed to preview the image within the browser using FileReader and FileReader.readAsDataURL as described here.

and I found a EXIF library which allows to extract the EXIF data of an image via javascript. But for me it only works if I use it with normal img tags which load their content over a URL.

I also found this question on StackOverflow where the accepted answer states that it is just not possible.

But I am pretty sure that it can be realized because 500px.com extracts the EXIF data immediately after a file is added for upload and before the upload has been finished.

Some ideas how it should be possible to extract the EXIF data from the base64 encoded image I get from the FileReader?

回答1:

I finally found a client side solution for the problem:

1. Read the file using the FileReader and the method .readAsBinaryString
2. Then wrap that binary string into a BinaryFile object which is already included in the EXIF Library
3. Finally call EXIF.readFromBinaryFile(binaryFileObject);

and its done :)

回答2:

jQuery-fileExif javascript library reads image exif data before upload.
GitHub link, example jsfiddle from the library.

var someCallback = function(exifObject) {

    $('#cameraModel').val(exifObject.Model);
    $('#lat').val(exifObject.GPSLatitude);
    $('#lng').val(exifObject.GPSLongitude);
    // Uncomment the line below to examine the
    // EXIF object in console to read other values
    //console.log(exifObject);

  }

      try {
        $('#file').change(function() {
            $(this).fileExif(someCallback);
        });
      }
      catch (e) {
        alert(e);
      }

回答3:

Have a look at the code of the FxIF firefox extension. It reads exif data using only JavaScript. To read the file contents, you can use the FileReader API of modern browsers.