Hills and valleys map

I understand how contour lines work, and am fairly good at reading contour maps to work out where the hills are. The difficulting is that it can be a slow process. I envisage a "hills and valleys" map that colours the map (apart from the detail) two colours: one for valleys; one for hills. It would take some calculation to work out where a valley starts and a hill stops, but roughly the valley should come to halfway up the hill each side. I think this kind of map would give a very quick (if basic) understanding of the lie of the land.