code: function ({ canvasId, x, y, width, height } = {}, done = () => {}) {
      return convertToImage(canvasId, x, y, width, height, 'bmp', done)
    }
docs: convertToPNG: function (width, height, done) { return convertToImage(width, height, 'png', done) }, convertToJPEG: function (width, height, done) { return convertToImage(width, height, 'jpeg', done) }, convertToGIF: function (width, height, done) { return convertToImage(width, height, 'gif', done) },