Shadow Under the sun and the sky
Following definitions may change as we work through the project
Hr, Hg, Hb : Intensity of a pixel for respective channels, on the lit-side of the candidate edge pixel
Lr, Lg, Lb : Intensity of a pixel for respective channels, on the darker-side of the candidate edge pixel
sr, sg, sb : Gradient magnitude of illumination
γr , γg , γb : Gradient direction for respective channels
wr, wg, wb : Shadow width for respective channels. Start with upper bound of width, and find local minimum and maximum along a line in gradient direction. The diff between the extrema location gives the width. Vary the upper bound for different scales.