Yep, we turned RGB into LUV space before extracting edges, which helps a lot on contrast and keeps essential edge information that could've been lost if converted to grayscale.

Agree with that 3D deformation is a difficult open problem, and we haven't gotten into that yet. Currently we assumed the document is a flat rectangle, which maps to a quadrilateral in image space. A homography is then applied to rectify it, and it seems to work quite well if the paper is slightly curved or folded.