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What is the difference between digital high ISO noise and film grain? Why does one "eat detail" and the other does not?

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    \$\begingroup\$ +1. This question is begging for some side-by-side comparisons... I'd love to see them. I searched a bit but came up short. \$\endgroup\$
    – Reid
    Jul 22, 2010 at 2:56

6 Answers 6

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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.

grains vs noise

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    \$\begingroup\$ Can the film grain be called noise at all? \$\endgroup\$
    – Karel
    Jul 22, 2010 at 3:06
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    \$\begingroup\$ It's not usually called noise, but it's a similar process since it depends on random processes. You can even see noise in your eyeballs: look at a flat white surface, and you can see fuzz swimming around. Same idea - random fluctuations in some part of the process lead to high-frequency variations in the image. \$\endgroup\$
    – Reid
    Jul 22, 2010 at 3:45
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    \$\begingroup\$ Interesting example and it gives some idea of the differences, but as the film has been digitized here already, you can't really say which pattern is caused by film grain and which by scanner noise. I'd bet some of the chroma noise in deep shadows is caused by digitization. \$\endgroup\$
    – Karel
    Jul 22, 2010 at 13:16
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    \$\begingroup\$ @Karel: That is an interresting point. The scanning process does of course add a small amount of noise, but I don't think that it's really visible. Noise from the scanner would be pixel sized like in the right image, but you can clearly see the larger grains from the film. Both are 1:1 crops of the images. \$\endgroup\$
    – Guffa
    Jul 22, 2010 at 13:52
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    \$\begingroup\$ Your image link is broken! Please fix it or host your uploads on our imgur account. Thank you. \$\endgroup\$
    – Kevin Vermeer
    Jun 22, 2012 at 14:33
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There's also the issue of chroma (color) vs. luma (brightness) digital noise. People generally find chroma noise more objectionable because it appears less natural; this is why noisy photographs sometimes work better in a B&W conversion. The better noise reduction algorithms can also address one or the other selectively.

I believe that film has pretty much only luma noise, which is one reason people sometimes find it less objectionable than digital noise.

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The biggest difference is the patterns in the noise. Film grain is caused by the grains of silver present in the film, and are not in a consistent pattern.

ISO noise is caused in the digital sensor and is pixel based, and therefore in a pattern.

Some feel that film gran is more pleasing because of the inconsistent pattern in which the noise occurs.

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  • \$\begingroup\$ I don't think the noise patterns are problem for modern digital cameras. \$\endgroup\$
    – Karel
    Jul 22, 2010 at 13:12
  • \$\begingroup\$ It's definitely a problem on my D90 at higher ISOs; a clear square pattern emerges. It's worse on some images than others obviously. \$\endgroup\$
    – Reid
    Jul 22, 2010 at 15:19
  • \$\begingroup\$ At low ISO values (less than 400 or so) it's not likely to be an issue on modern digital cameras, but depending on the model it is still quite prevalent, especially if you are maxing out your ISO in low light to get the shot. \$\endgroup\$
    – chills42
    Jul 22, 2010 at 15:38
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Higher ISO film tended to have more grain; and higher ISO digital shots exhibit more noise - a similar cause, but the visual appearance is different.

Digital ISO noise is related to the size of each pixel, as the noise is per-pixel (so the more pixels you have, the less obvious noise is when viewed the same size), whereas with film, the noise is per crystal - you need larger crystals for higher sensitivity.

One analogy I've used in the past to demonstrate this is to ask several people to time with a stopwatch how long it takes a car to drive around a car park, and then to time how long a person takes to do the same journey - because the person is slower, the margin of error is a smaller in proportion to the overall figure, even though different people will give timings to within a few seconds of each other.

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  • \$\begingroup\$ I thought lower ISO film has more grain?! \$\endgroup\$
    – txwikinger
    Jul 22, 2010 at 15:03
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    \$\begingroup\$ @txwikinger lower sensitivity == higher ISO number == more noticeable grain/noise \$\endgroup\$
    – Rowland Shaw
    Jul 22, 2010 at 16:21
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One interesting difference is that digital camera noise to a good degree is quantization noise related to the imaging process. This can go as far as to "ISO invariant" sensors where the ISO setting does not affect the raw image capture anymore but instead determines what exposure the camera aims for and how the raw values are then interpreted. For such a sensor, the noise level depends on the actual exposure but not on the set ISO value.

In contrast, the choice of ISO/ASA level for film determines the film grain. An ASA100 film underexposed by 3EV retains its fine grain compared to an ASA800 film but loses its contrast. If you bring up the contrast in enlarging, you get more of a dot-dithered look than a coarse-grained one.

Some digital cameras have the ability to use higher ISO values at reduced resolutions: that is a bit more like what higher ASA films do with their coarser grain even though the digital camera "grain" is a rectangular pattern while the film grain is irregularly spaced.

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Huge difference.

Film grain is more like a texture that brings to life the images.

Noise is a defect of the sensitivity of the camera to the light. Noise is the result of the interpretation of the light in an image that the camera can't capture. The camera can't capture light in low light situations so it invent the colours that the sensor can't caught. So this noise is not the representation of a real image is an interpretation of what the sensor thinks the could be there.

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    \$\begingroup\$ This doesn't seem right to me. Can you describe how the camera "invents" colors? \$\endgroup\$
    – mattdm
    Jan 5, 2016 at 17:05
  • \$\begingroup\$ Camera cannot invent. Camera retrieves light with a sensor and then processes a signal (coming from the sensor). \$\endgroup\$
    – Dragos
    Jan 5, 2016 at 17:20

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