1. A method of measuring a surface strain of a band in a material sheet, the band having a width, the method comprising: marking a single line traversing the width of the band at an angle before deformation; deforming the band; obtaining an equivalent two-dimensional image of the line after deformation by a method comprising: obtaining plan view and profile view images of the line after deformation; and performing a three-dimensional to two-dimensional transformation using the plan view and profile view images of the line after deformation; comparing the line before deformation with the two-dimensional equivalent image of the line after deformation; and determining the strain in the band after deformation.