[jsr-314-open] begin success complete and rendered?

I have an Ajax request that pulls an image from a web service. I'm using f:ajax's onevent attribute to display a progress bar when the Ajax call begins, and make it disappear when the call is complete, but complete does not coincide with the end of rendering, so there's sometimes a considerable lag between when the progress bar disappears, and when the image is fully drawn. Is there a way to send a notification when rendering is complete, so I can avoid the lag time? Thanks, david