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Multispectral household plastic classification for recycling using a camera array
Summary
Scientists built a low-cost scanning system using nine special cameras to quickly identify different types of household plastic, correctly sorting them about 87% of the time. Better plastic sorting means more materials can actually be recycled instead of ending up in landfills or breaking down into microplastics that pollute our water, food, and eventually our bodies. Since the system uses affordable, readily available parts, it could realistically be adopted by recycling facilities to improve how much plastic gets a second life.
Abstract Plastic pollution has become a persistent problem in natural ecosystems. Driven by insufficient waste management, limited recycling efficiency, and high costs for recycling, plastic waste in the environment poses significant ecological and health risks. Recycling requires accurate identification of polymer types, but existing optical sorting systems often struggle to distinguish common household plastics. In this work, we present a novel classification approach based on a multispectral imaging system consisting of nine cameras equipped with near-infrared bandpass filters. The system is designed to discriminate the seven most common household plastics. From the resulting multispectral images, we extract the spectral fingerprints and derive features such as intensity differences between specific wavelength pairs and their slopes, as well as false-color image representations. A dedicated preprocessing pipeline aligns and normalizes the data before classification. We recorded a multispectral household plastic database ( https://github.com/FAU-LMS/MHPM ) and trained four different classifiers Gradient Boosting, Extreme Gradient Boosting, Light Gradient Boosting Machine, and CatBoost. The best-performing model achieves a classification accuracy of 86.7%. The computational runtime is 2.603 $$\upmu$$ μ s per pixel, enabling efficient processing of high-resolution images. The entire setup is built from off-the-shelf hardware components, which makes replication straightforward and allows direct integration into industrial sorting pipelines.