Identifying Planetary Nebulae Candidates from IPHAS and VPHAS+ Surveys via YOLO Deep Learning Models

We present a deep learning detection method capable of effectively identifying planetary nebulae (PNe) on IPHAS and VPHAS+ surveys. Our detection pipeline is based on the YOLO architecture and is adaptable to other datasets. Using the HiPS system, we preprocess and augment the r, i, and Hα bands to produce two red, green, and blue (RGB) image datasets: (1) 640 times 640 px images at full resolution, and (2) 1 280 times 1 280 px images designed to capture extended objects up to 0.2 deg. Images of about 2600 PNe are labelled using the HASH database. The loss function and evaluation metrics are adapted to the diffuse and low-contrast nature of PNe; a very low intersection over union (IoU) threshold (1%) is used. A k-fold cross validation shows that the YOLOv12m model achieves an average precision of 0.979 on the first dataset. At a confidence threshold of 0.15, it achieves a precision rate of 98.7% and a recall rate of 97.4%. We deployed our system (on 1280 times 1280 images) on the full surveys' coverage (about 3755 deg squared), and present a preliminary analysis of the detection results. The system is robust against artifacts such as CCD corner defects and HiPS tile joints. Our convolutional-neural-network-based model achieved excellent results on the test set, comparable to-or exceeding-that of a recent Swin Transformer approach. However, a challenge persists when applying deep learning models to extensive and densely populated Galactic fields: the development of an automated system that can effectively discriminate PNe from mimics that human experts are able to distinguish (e.g., H II regions). We outline possible improvements for future work.