The food isn't fancy, but it's certainly an 'improvement over' what we're served at school.
His cooking needs 'improvement'. = There's still 'room for improvement' in his cooking.
The editor made some 'improvements' to/in the article before it was printed.
(..) Insert key. Left and three, two, one, turn. How are wife and kids? - Great, thanks. So what do you think, Doctor? I've shown improvement, haven't I? Well, Sarah, here's the problem: I know how smart you are. You're just telling me what I want to hear. (..)1991 Terminator 2: Judgment Day
(..) much improved lately. It has helped to have a goal, something to look forward to. And what is that? You said that if I showed improvement after six months, you would transfer me to the minimum security wing and l could have visitors. Well, it's been six months. I was looking forward (..)1991 Terminator 2: Judgment Day