An experimental platform for high-speed video recording of fuel jet spraying and applicability of the platform for studying the liquid fuel jet spraying are discussed in the paper. Fuel spraying quality is evaluated by the jet cross-sectional area. Axial section data show the dynamics of normalized brightness areas of diesel jet and RME values within the injection pressure range from 60 MPa to 180 MPa. A pixel separation method for the fuel jet image with clusterization to determine object boundaries is proposed. The region of interest of a fuel jet (i.e. an area on an image) is shown with a low brightness and indicates a high fuel concentration while an area with a high brightness indicates a low fuel concentration. It is shown that the brightness of fuel jet areas is dependent on fuel spraying quality when fuel sprayed by various sprayers under various conditions. In accordance with the research results, the following conclusions are presented: the increasing of the injection pressure at a given time increases the jet crosssectional area; the high fuel concentration area is located in the center at the beginning of the fuel jet where the jet is not yet disintegrated. The increasing of pressure from 60 MPa to 180 MPa results in increasing of jet dark area disintegration time from 1.2 ms to 1.4 ms. A jet with higher injection pressure has greater length and later disintegration time; the increasing of injection pressure results in the growth of the high-concentration area while areas with lower concentrations are diminished. Conditional time-related maximums of jet areas are shifted to greater values. Eventually, areas with high concentrations are consequently replaced by areas with lower concentrations leading to enlargening of the area with the highest brightness.