add unit/integrted tests for dpc

This docstring is ambiguous, is it [top, left, length, width] or [left, top, length, width].  I also expect that length is a horizontal dimension as is width.  I would use 'height' for one of the dimensions.  Is 'upper left' with (0, 0) in the top left or lower right?

I would also suggest using row/col instead of height/width etc to avoid any ambiguity.  This is the naming convention that scikit-image is moving towards at it make sense to stay consistent with them.