US Patent 7436504 Non-destructive testing and imaging

A method of non-destructive testing includes non-destructively testing an object over a range of test levels, directing coherent light onto the object, directly receiving the coherent light substantially as reflected straight from the object, and capturing the reflected coherent light over the range of test levels as a plurality of digital images of the object. The method also includes calculating differences between pixel values of a plurality of pairs of digital images of the plurality of digital images, and adding the pixel value differences of the plurality of pairs of digital images to yield at least one cumulative differential image.