Dual-energy X-ray imaging (DEXI) has a wide range of applications in various fields such as medical diagnostics and security. However, existing DEXI systems face significant challenges that require immediate resolution, including high preparation costs, excessive cumulative radiation doses and low resolution. In this study, we developed a soft X-ray film detector based on lead thioantimony (Pb2SbS2I3) using the spin-coating technique. This method not only reduces fabrication costs but also achieves high sensitivity (9669 μC Gyair-1 cm-2) and a low detection limit (71 nGyair s-1), making it one of the top-performing soft X-ray detectors reported to date. By simply placing the film in front of a normal X-ray detector, we constructed a novel DEXI system that enables dual-energy detection within a single exposure, thereby enhancing material discrimination while reducing the cumulative radiation dose. Additionally, it provides imaging resolution (7.2 lp/mm) comparable to commercial products, and its compact thickness (20 μm) does not compromise the resolution of other detectors. This work opens new applications for metal chalcohalides in X-ray detection, enabling precise soft X-ray imaging within a single exposure for the first time.  These advancements are expected to have significant implications for cutting-edge applications such as bone density measurement, energy-dispersive computed tomography, intelligent security screening, and space exploration.