<p>To address the issue of misjudgment in traditional connected domain marking algorithms during the dense assembly and welding of SMT components, a method combining connected domain marking with localized watershed algorithms has been proposed. After preprocessing the component images, including grayscale conversion and noise filtering, the connected domain marking algorithm’s identified soldered areas are masked and processed. The soldered areas are then extracted, histogram equalization and distance transformation are performed, and the watershed algorithm is used to segment the misjudged soldering areas. An SMT solder defect detection test bench was developed on the LabVIEW platform, and a comparative experiment was conducted with traditional connected domain algorithms. The experimental results demonstrate that the optimized algorithm not only maintains the accuracy of traditional connected-component labeling but also significantly reduces the false-positive rate in densely soldered environments. Consequently, it exhibits stronger adaptability and robustness to interference, better fulfilling the requirements of real-world engineering applications. This method exhibits superior environmental adaptability and markedly higher interference resistance, rendering it well-suited to real-world engineering applications.</p>