During the operation of marine internal combustion engines, the procedure for indicating the working process in certain operating modes is widely used, followed by an analysis of indicator diagrams and a comparison of the results obtained with the reference ones obtained during engine factory tests. However, the general trend in the world fleet towards a decrease in the commercial speeds of ships, on the one hand, and the use of tight traffic schedules, on the other hand, have led to the fact that in most cases it is impossible to carry out indexing according to the procedures prescribed in the rules for the technical operation of engines. Thus, the ability of maintenance personnel to objectively assess the current technical condition of the engine is lost, and to determine the necessary list of preventive measures for maintenance and repair, which, of course, affects the efficiency of engines and the safety of navigation in general. One of the effective ways to solve this problem is the use of digital profiles of engine work processes, which characterize their work in the entire range of operating modes. With the help of a digital profile, it is possible to obtain a calculated reference indicator diagram, which can be used for comparison with the one obtained during the planned indication of the engine in any mode of its operation. As a basis for building digital profiles, it is appropriate to use the results of acceptance test bench tests of the engine by the manufacturer. However, taking into account the rather long service life of marine engines, test reports usually exist only in a raster format, which greatly complicates the processing of the indication results given in them, which, most often, was performed using mechanical indicators. To use this information to build digital profiles, the authors proposed a method for processing such indicator diagrams, described in previous articles. However, the efficiency of generating digital profiles significantly depends on the quality of the basic diagrams on which these profiles are built. This article is devoted to the processing of such diagrams.