infrared cleaning

Infrared cleaning is a technique used by some film scanners and flatbed scanners to reduce or remove the effect of dust and scratches upon the finished scan. It works by collecting an additional infrared channel from the scan at the same position and resolution as the three visible color channels (red, green, and blue). The infrared channel, in combination with the other channels, is used to detect the location of scratches and dust. Once located, those defects can be corrected by scaling or replaced by inpainting. Method The three color dyes in typical color film emulsions are largely transparent to infrared light, so the infrared image is almost uniformly clear, unlike the RGB images. On the other hand, dust absorbs and scratches scatter the infrared. Any dust spots or scratches appear as dark marks in the infrared, making them easy to find and compensate for. Pixels that are partially occluded (for example, the dust only obscures a small portion of the pixel) may be corrected by scaling. The infrared pixel value indicates the fractional amount of the occlusion, and RGB values can be scaled appropriately. If most or all of a pixel is occluded, scaling is not feasible. Instead, the pixel value may be interpolated from nearby good pixels (inpainting).