Non-destructive testing methods are used in an increasing number of applications, some of which require precise knowledge of the relative position between transducer and surface. Conventionally, this has been determined using a contact method such as a linear/rotary encoder. An alternative
is demonstrated here, using a digital camera and the phase correlation technique. Linear sample movement has been determined to sub-pixel precision, confirmed manually as a median accuracy of 0.01 mm of linear movement (0.06 of a pixel) in this case, despite uneven illumination and the use
of a basic low-resolution camera.