Proportional constraint for seam carving

Seam carving is an image processing operator for content-aware image resizing [Avidan and Shamir 2007]. It generates an energy map from gradient intensity of pixels and searches for seams, which are vertical or horizontal continuous paths of pixels that run through local minimum energy areas. Removing or inserting pixels along a seam enables users to shrink or enlarge pictures by a wide range, while still retaining all details of the image.