1. A method of non-destructive testing comprising: 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; capturing the reflected coherent light over the range of test levels as a plurality of digital images of the object; 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.