Weed detection in blackgram fields under occlusion and class imbalance using SA–ANMS Faster R-CNN

Sustainable agriculture has been greatly challenged by the problems of dense canopies that result in extreme occlusion, scale disparities and imbalances of classes, making it difficult to detect small and overlapping weeds in real field conditions. Actual blackgram fields in Karnataka, India, were used to generate a dataset that featured a high level of crop to weed contest, and exhibited a significant amount of scale diversity, with 75 percent of objects comprising less than 0.8 percent of the image space. To address these challenges, the paper presents a better Faster R-CNN framework that adds five modules, i.e. Spatial Attention (SA), Multi-Scale Fusion (MSF), Context-Aware RoI, Shape-Aware Prediction and Adaptive Non-Maximum Suppression (ANMS). The research shows that with larger architectural complexity, there is no guarantee of better performance through an extensive ablation study involving 32 model configurations. The best two-module combination (SA + ANMS) obtained the highest F1 -score of 0.9547, precision of 0.9439, recall of 0.9658, and a mean Intersection over Union (mIoU) of 0.9445, and inference speed of 4.42 FPS, which was higher than the full five-module version. It is important to note that only 12.5% of configurations were better than the baseline, highlighting the fact that too much module stacking may hurt performance. The analysis shows that there is a high positive synergy between SA and ANMS and that the MSF module competes slightly on features. The novelty of this work lies in the systematic exploration of how various enhancement modules can be interacted to function as a single detection framework and show that the selective combination of modules can produce a better outcome than random stacking. Especially, the finding of a complementarity, optimum minimum combination of SA + ANMS confirms that the efficiency-based design is used, not complexity-based expansion. It provides informative insight on designing efficient detection system for precision agriculture applications by revealing the impact of wise module selection instead of architecture complexity on obtaining consistent weed detection against occlusion and inter-class inconsistencies.