ObjectiveAt present, psoriasis area scores are measured manually by dermatologists through visual observations. This subjective method suffers from numerous typical problems. The only solution to these problems is to design and implement objective methods for this. However, most of the existing works in this regard are based on machine learning frameworks that are semi-automated and feature-dependent. In this work, a deep learning-based fully automated, and single-stage framework is proposed to detect psoriasis lesions and measure their area score from color images of human body regions. MethodsThe proposed method is an extension of the existing PsLSNet proposed by our team, which provides a fully automated approach for the segmentation of single psoriasis lesions from cropped patches of skin images. For this proposed work, a new version PsLSNetV2 model is developed for automated segmentation of healthy skin, multiple psoriasis lesions, and background region simultaneously in complete body region images. This proposed model utilizes an efficient and lightweight network with transfer learning to increase the representational efficiency for multi-class segmentation. ResultsThe proposed model is tested by 5-fold cross-validation on a self-generated dataset having 500 images from 100 psoriasis patients. The multi-class segmentation performance of the proposed model achieves an overall Dice-Coefficient Index and Jaccard Index of 97.43% and 95.05% respectively and outperforms the existing models. ConclusionThe fully automated multi-class segmentation results by the proposed lightweight segmentation model are promising enough to determine psoriasis area score objectively with an average accuracy of 94.20% for assisting dermatologists in a simple and rapid way.