text – How to blur an image halfway/not fully in keynote?

I’m making a keynote presentation (animation, really) where there’s an image on the slide. Next, after a few seconds, some text moves in on top of the image, and what I want is for that image to simultaneously blur (albeit not fully – maybe 50% blur, kinda like they do in movies when focusing on one person and not the other, if you know what I mean). I know there’s a blur animation, but when I tried it, it fully blurred out the image. Can someone please help me? Thanks.