Autodesk 62205-051408-9001 User Guide - Page 726

27 Adding and Removing Grain Grain in images can be either beneficial or detrimental. The Add Grain and Remove Grain operators allow you to manage the graininess of your clips. About Film Grain The physical structure of film is a flexible support coated with emulsions of gelatine and light-sensitive silver halides. The silver halide crystals vary in size, shape, and sensitivity, and are randomly distributed within the emulsion. These crystals form clumps which are visible as grain. Fast films have a greater proportion of large crystals which form larger clumps, and therefore appear grainier. In areas of the image with less exposure, the largest crystals respond to the light, so shadow areas of negative contain the most grain. In well-exposed negative, these areas print very dark and the eye cannot distinguish the grain. Midtone regions display the most apparent graininess. Combustion includes two operators that manage grain in clips. It is possible to add grain to or remove grain from the RGB channels in any image using the Add Grain and Remove Grain operators. Grain in an image can be either beneficial or detrimental to your clips. In the background of an image, graininess can make it difficult to pull a clean and effective key. As an added effect, graininess can be effective in synthesizing a film quality in a video image. Removing Grain from Clips The Remove Grain operator is a general noise reducer that removes noise, softens the image, and selectively restores the sharp details of an image. In some cases, it may be best to remove the grain completely, and then manually restore the desired amount of grain using the Add Grain operator. In other cases, you may have material with completely different grain signatures that need to be composited together. It is then a good idea to remove the grain from one, and give it the grain of the other. With the Remove Grain operator, you can: • Remove grain from a film-originating image to transfer or match it to video quality. • Remove film grain from old film footage. • Remove noise on video clips. • Reduce the size of grain on images printed on film that was push-processed to compensate for overexposure or underexposure. • De-grain images before creating a matte to obtain a more precise result. Note: The amount of grain in each channel of a color is not generally uniform. Usually, the blue channel contains more grain than the red or green channels. Therefore, you obtain the best results using the Remove Grain operator if you de-grain each color channel separately. Using the Remove Grain Operator The Remove Grain operator consists of two filters: • An RGB-averaging filter that removes noise and softens the image. • An RGB-sharpening filter that selectively restores the sharp details of an image. 710