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To start an image-based coatings assessment, photos of the port and star- board sides of the ship's overall topside freeboard (the exterior hull of the ship from the waterline up to the main deck) are taken as reference points, says NRL research team member James Tagert with Vision Point Systems, Inc. (Fairfax, Virginia). Each side of the ship is then typically divided into zones, with the number of zones varying according to the size of the ship. A set of overlapping pho- tos is taken for each zone using the cam- era's zoom feature to capture the details of the coating's condition on as much of the ship's freeboard as possible. The preferred digital camera for the assess- ment is the Canon SX 30 IS†
with a 20:1
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in past work by the NRL to render color with the repeatability necessary for the coatings assessment software program to provide consistent analyses. The inspec- tors stand as close as 100 ft (30.5 m) to the ship to photograph the freeboard coating alongside the dock and as far away as 1,200 ft (366 m) to capture images of the freeboard coating on the opposite side of the ship from an adjacent pier. For most U.S. Navy surface ships, such
as destroyers, cruisers, and amphibious vessels, the entire topside can be photo- graphed in less than one day while the freeboard and catwalk of an aircraft car- rier can be photographed in less than three days. Complete image sets can contain anywhere from six to 30 images, with large ships such as aircraft carriers or ships that have areas with observable coatings failures requiring a larger num- ber of photos in an image set. Currently, the images are manually
entered into the Automated Freeboard and Topside Coatings Analysis Toolset (AFTCAT), a set of advanced image
† Trade name. NACE International, Vol. 51, No. 3
processing and data interpretation algo- rithms that analyze the high-resolution photographs of a ship's freeboard coat- ings for coating anomalies. By looking for color variations in the photos, Wegand explains, the algorithms are able to iden- tify and provide a quantitative measure- ment of corrosion damage and color non-uniformity, as well as determine the extent of flaking, delaminating, and blistering. In the AFTCAT, the most advanced
and proven algorithm is the Topside Cor- rosion Detection Algorithm (TCDA), which calculates the percentage of actual corrosion damage in the analyzed photo and generates an output image that high- TQOP\[ QLMV\QÅML KWZZW[QWV ][QVO ZML QUIOM overlays. The TCDA is an extension of the Tank and Void Corrosion Detection Algorithm, a standard and recommended method for assessing the coating condi- tion of tanks and voids on U.S. Navy ships, and has been demonstrated in a series of shipboard topside coatings and corrosion damage assessments since 2006, comments Wegand. The coatings non-uniformity algo-
rithm, also part of the AFTCAT, uses a unique image processing filter on the photographs that enhances slight differ- ences in coating hues. This enables the program to identify areas where coating overcoats and touch-ups have been ap- plied and areas where coatings have faded, and calculate the percentage of the freeboard coating that is non-uniform.