A convex quadrilateral is a four-sided polygon whose corners define a useful image boundary. In phone scanning, its four photographed corners can represent a flat rectangular page distorted by perspective. section 4.4.1
The scanning workflow treats the geometry as a sequence of simpler transformations:
- Map each target-rectangle pixel to its source position rather than transforming the photographed quadrilateral directly into a rectangle. section 4.4.1
- Scale the rectangle into a standard unit square with corners (0,0), (1,0), (1,1), and (0,1). section 4.4.1
- Solve the four-point projective system in smaller stages instead of handling one large symbolic system. section 4.4.1
Undoing a photographed page
Given four corner correspondences between a rectangular target and a photographed convex quadrilateral, compute where every target pixel originated, then sample that source color to reconstruct the flat image. section 4.4.1
