rwSALT: a regrowth-weighted SALT score providing direct pixel-level measurement rather than visual estimation

Open-source browser-based tool for pixel-level SALT score calculation from scalp photographs. Supports manual painting mode (alopecic ×1.0, regrowth ×0.5), auto-calibrated mode with continuous hair-density measurement via CIE Lab* colour space calibration, adjustable alopecia threshold, density map overlay, and androgenetic alopecia exclusion. Developed to improve reproducibility and sensitivity to partial regrowth in alopecia areata, particularly in patients receiving JAK inhibitor therapy.