bitmap extrusion wall expansion

Ok. This can't be too hard to understand? eh?

This is a bitmap created from an indoor scan of a Mall.

I've been using them to be extruded into 3d models.

(inserted below)

however, This is really messy and instead of having dugout-type hallways, I want to have building-like walls. To do this, the black pixels on the edge of the scan need to be combined and thickened. Is there any way I can outline or expand the size of each black pixel to join with the next black pixel and make a wall?

sorry if it's confusing. here's an example of what im looking to do.

Yes, this is very rough, and there's probably no way to make it complete the line all the way around, but can I use those black pixels on the edge to connect somehow or bleed outwards so it's more than one or two pixels of edge all the way around?

thanks

-Jon