**Background:** Rice plant counting is essential for yield estimation, growth diagnosis, disaster loss assessment, and breeding. Traditional manual counting is labor-intensive, time-consuming, prone to human error, and limited to small sampling areas. Existing automated methods for other crops (corn, wheat, maize) cannot be directly applied to rice due to differences in plant morphology, imaging conditions, and dataset characteristics. The authors aimed to develop a deep learning approach using affordable UAV RGB imagery to simultaneously count, locate, and size rice plants in paddy fields.
**Methods:** The authors collected RGB images using a DJI Phantom 4 Advanced quadcopter UAV at 7 m altitude with vertical downward shooting, front overlap of 80%, and side overlap of 70%. Images were captured every three days during tillering to jointing stages from 2018–2020 in Nanchang, Jiangxi Province, China. The resulting URC dataset contains 355 images (original resolution 5,472 × 3,648, downsampled to 1,368 × 912 for training) with 257,793 manually labeled center points. RiceNet architecture uses the first 13 layers of VGG16_bn as a feature extractor, followed by three decoder modules: density map estimator (DME) with plant attention mechanism, plant location detector (PLD) using local non-maximum suppression, and plant size estimator (PSE). A novel positive-negative loss function was introduced to suppress background false positives. Training used Adam optimizer with learning rate 1×10⁻⁴, batch size 3, and hyperparameters λ=0.1 and γ=0.1. Performance was evaluated using MAE and RMSE.
**Key Results:** On the URC dataset, RiceNet achieved MAE of 8.6 and RMSE of 11.2, outperforming MCNN (MAE 25.5, RMSE 34.1), CSRNet (MAE 12.9, RMSE 17.5), SANet (MAE 10.1, RMSE 13.4), TasselNetV2 (MAE 29.5, RMSE 39.4), and FIDTM (MAE 26.3, RMSE 31.5). Compared to TasselNetV2 and FIDTM, MAE improved by 70.8% and 67.3%, respectively. On the MTC maize tassel dataset, RiceNet achieved MAE of 3.4 and RMSE of 5.3, with 81.0% MAE improvement over MCNN. On the WED wheat ear dataset, RiceNet achieved MAE of 3.7 and RMSE of 4.6, with 67.8% MAE improvement over MCNN. R² values were 0.997 (URC), 0.957 (MTC), and 0.975 (WED). Ablation experiments showed positive-negative loss reduced MAE from 10.6 to 8.6 for RiceNet, and from 25.5 to 11.7 for MCNN. Optimal Gaussian kernel size σ was 6. The network also demonstrated robustness to sun reflection and raindrops in field conditions.
**Clinical Implications:** While not a clinical study, this agricultural technology has significant implications for food security and crop production. Accurate, automated rice plant counting enables more effective planting density management, objective disaster assessment from typhoons and floods, and improved rice breeding through precise phenotyping. The ability to estimate plant location and size from point-level annotations (rather than expensive bounding box labels) makes the approach practical for large-scale deployment. The authors note limitations including sensitivity to weeds, sun reflection on water, and the need for further research on quantitative evaluation of location and size estimation. Future directions include developing networks robust to sun reflection, further suppressing false positives, and creating lightweight versions for field robots and embedded platforms.