Converting line art to shaded art

I discovered that seemingly simple black-and-white line drawings with lots of strokes tend to have huge file sizes when converted to vectors. I doubt that there's any remedy, but I just wondered if anyone is aware of any technique or software program that can convert more or less merge the strokes to shaded areas?

In the end, I'll probably have to just look for images that are shaded to begin with. Do you know if there's a name for that category of drawings? I suppose watercolors would even work; they could either be transformed to color or black-and-white vectors.

Thanks.