Speckle noise reduction in optical coherence tomography of paint layers

We present and characterize a sequential angular compounding method for reducing speckle contrast in optical coherence tomography images of paint layers. The results are compared with postprocessing methods, and we show that the compounding technique can improve the speckle contrast ratio in B-scans by better than a factor of 2 in exchange for a negligible loss of resolution. As a result, image aesthetics are improved, thin layers become more distinct, and edge-detection algorithms work more efficiently. The effect of varying the angular scan size and number of averages is investigated, and it is found that a degree of statistical correlation between speckle patterns exists, even for relatively large changes in angle of incidence. Angular compounding is also performed on three-dimensional data sets and compared with a method whereby en face slices are averaged over depth.