A special dye applied to the back of most photographic films that absorbs light passing through the emulsion. This prevents light from reflecting off the camera's film plane or backing and re-exposing the emulsion, which can cause halation or unwanted halos around bright areas in an image. Antihalation backing improves image sharpness, contrast, and overall clarity, and is particularly important in high-contrast scenes, night photography, and film formats where precise detail and tonal accuracy are required.