Get progress when piping through gm

Question

On my node app I'm trying to figure out how to see the progress of the stream. How can I get tell the browser what the progress is?

This is the code I'm using on the server:

gm(readStream, 'img.jpg')
   .resize(width, height)
   .quality(quality)
   .stream(function (err, stdout, stderr) {
        stdout.pipe(res);
    });