tVisual density is an important index for the estimation of photographic film and visual photo. The development of biomedical image and macromolecule image needs high measurement uncertainty of visual density in spectrum characteristic. The ISO standard of visual density measurement conditions was modified in 2001. A series of equipments designed for densitometer enhance the spectral matching between the national standard densitometer and the ISO standard function. And a new measurement formula is given based on theory analysis. According to the measurement data and uncertainty analysis, the combined uncertainties are 0.001 1 (0