About Granularity and Graininess

Granularity is the objective measurement of the size of grain clusters across an area of uniform tone. It is high in dark regions and midtones, and low in highlights.

The granularity curve represents the granularity from the shadows up to the highlights. For an image with 8 bits per color channel, the X-axis of the curve ranges from 0 to 255. If you are working with 10 bits per channel, the range is from 0 to 1023.

The film emulsions listed in the Film Stock list on the Add Grain Controls panel have specific granularity curves provided by the manufacturer (Kodak). Each type of film stock has a distinct grain "fingerprint" which is described by the granularity curve. Since the fingerprint is so specific, all elements of a composite need to have been shot on the same stock.

Instead, you can de-grain elements (with various fingerprints) before you create the mattes, and then re-grain the entire composite afterwards to match the grain. For example, apply a Remove Grain operator before the Keyer for the foreground layer, another on the background layer, and apply the Add Grain operator after the composite.

Graininess is the subjective perception of the amount of grain. The eye is distracted by fine detail, bright highlights, or busy movement, paying less attention to grain in such cases. A sharp image appears less grainy than when poorly focused. Large areas of uniform tone reveal grain patterns most clearly.