What’s the difference between high-ISO digital noise and film grain?
Asked 7/21/2010
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Why do photographers often find film grain more pleasing than digital high-ISO noise? Is it true that digital noise “eats detail” while film grain does not, and what roles do luminance, color noise, and patterning play?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
16y ago
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The size of the grains in the film varies depending on the film sensitivity. The more sensitive the film, the larger the grains. Digital noise is always the size of a pixel, regardless of the ISO setting.
Film grain is color neutral, as it consist mostly of luminance differences. Digital noise consists of both luminance and color differences, and is most visible in the blue color channel.
In the more recent digital cameras the digital noise is quite even. In earlier models the noise had more banding and patterns. The film grain doesn't have any banding or patterns, so it's seen as pure noise. If the digital noise has any banding or pattern, the brain can easily pick that up, and that is more disturbing than pure noise.
Neither grain nor noise eats detail. It's noise reduction that eats detail, as it can't tell the difference between small details and noise. Noise reduction is used on digital noise, but it can also be used to reduce film grain.
There is an example below. On the left is the film grain from a Kodak Gold ISO 200 film. On the right is the digital noise of a Canon EOS 5D Mark II @ ISO 3200. Notice the blue noise in the dark areas in the right image.
Originally by user149. Source · Licensed CC BY-SA 4.0
user149
16y ago
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Film grain and digital noise are different in both appearance and cause. Film grain comes from the film’s silver grains; faster film generally has larger, more visible grain. It is mostly luminance variation, with a random, non-repeating look, so many people find it more natural or pleasing.
Digital high-ISO noise comes from the sensor/electronics and appears at the pixel level. It can include both luminance noise and chroma (color) noise, and color noise is often seen as more objectionable. Older digital cameras could also show patterned noise or banding, which is especially distracting because the eye notices structure more than random texture.
Strictly speaking, neither grain nor noise directly “eats detail.” What reduces visible detail is usually the way noise overlaps fine detail, or the use of noise reduction to smooth it away. Digital noise reduction can blur texture and edges if applied aggressively. Because film grain is more random and mostly monochrome, it often masks detail less offensively than color or patterned digital noise.
That’s also why noisy digital images often look better converted to black and white: removing chroma noise leaves mostly luminance variation, which feels more like film grain.
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