Spatially resolved optical characterization of large-area electrochromic devices using digital image-based spectral reconstruction

The optical characterization of large-area electrochromic (EC) devices remains a significant challenge, particularly when aiming to evaluate spatial uniformity, switching kinetics, and long-term stability with high precision. Traditional methods based on UV–Vis spectrophotometry provide accurate spectral data but are inherently limited to small sampling areas and cannot capture spatial variations across full devices. In this study, we validate a digital image-based system capable of reconstructing visible-range transmittance spectra from photographs and videos using calibrated color correction and neural network-based spectral reconstruction. The system has been used to quantify four core electrochromic performance indicators for devices of aprox. 40 cm 2 area, namely color homogeneity, optical contrast at any wavelength within the visible range, switching speed and cycling stability. Characterization is simultaneously obtained for the whole device surface, delivering quantitative color-coded maps at high spatial resolution. Validation was performed for a set of polymer electrochromic devices covering a complete visible color gamut. The resulting maps successfully revealed non-uniformities in contrast, kinetics, and degradation across the devices—patterns that would not be detectable using conventional single-point measurements. The method demonstrated strong correlation between visual and quantitative degradation indicators. While this work focuses on electrochromic systems, the proposed approach is broadly applicable to any large-area device which performance is linked to visible-range transmittance. This tool provides a fast, non-invasive, and scalable alternative to spectrophotometry, opening new possibilities for the optical evaluation of smart coatings, thin films, and other functional materials. • Image-based system quantifies optical response over entire EC device surfaces. • Real-time maps of contrast, switching speed, and stability are generated. • Validated with electrochromic polymers covering full visible color range. • Enables scalable, non-invasive optical evaluation beyond single spot measurements.