ACCU-ND is a surface coating technology used in photographic filters. Its purpose is to ensure that so-called 'neutral gray filters', also known as ND filters, truly do not alter colors in the resulting photograph or video. A common problem with some ND filters is that they cause a color shift, for example into red or green hues. ACCU-ND technology prevents this by having the applied layer absorb light uniformly across the entire visible and infrared spectrum. As a result, there is no color distortion, and the image retains its natural color rendition, with only its overall brightness reduced.