You can also use an event listener.
I have an ajax call that downloads an image after it's cropped by Ink. This call was failing sporadically. I fixed it by doing roughly the following:
filepicker.convert(myBlob,
{
crop: cropDimensions
},
function(croppedBlob) {
function downloadImage() {
...
}
var imageObj = new Image();
imageObj.onLoad(downloadImage()); //only download when image is there
imageObj.src = croppedBlob.url;
}
);