问题
Is it possible to parse an image object (<img>) in the DOM as if it had been uploaded and opened with FileReader? I am trying to use jpegmeta.js to extract EXIF metadata from JPEGs, but it needs binary strings which are returned by the FileReader.
It might be possible to use XHR to load the image from its URL and parse it with FileReader. However, this would incur a lot of overhead if every image has to be downloaded twice. Another option could have been to use the canvas, but that loses the exif data when converting.
回答1:
The general consensus seems to be summed up in this answer: Get image data in JavaScript?
So if you need the exif data, you'll need to use the XHR technique. Hopefully the browser will have the image cached, so it won't be too much of a performance hit. Otherwise the canvas technique should do the job.
来源：https://stackoverflow.com/questions/13375333/how-to-convert-an-image-object-to-a-binary-blob