Film grain vs digital noise: what is the difference?

What is film grain?

Film holds light-sensitive crystals in a coating. After development, those crystals or the dye clouds that replace them make up the picture, and at high magnification they show up as a texture. Wikipedia describes the physics under film grain.

The effect is random but not chaotic. Grain size follows the film. Faster films use larger crystals to catch more light, so they look coarser. Slower films are finer.

What is digital noise?

A phone sensor counts light with millions of tiny photosites. In dim light the signal is weak, so the camera boosts it, and the boost also amplifies random electrical variation. The result is speckles of color and brightness, covered in Wikipedia's article on image noise.

Phones fight it with noise reduction, which smooths the speckle and can also smear fine detail. That is why a dark iPhone photo can look waxy.

Why do people like grain?

Grain gives a flat surface something to look at. It softens edges, hides the clinical sharpness of a modern sensor and reminds people of prints from a drawer. It also behaves well in shadows, where noise tends to turn into colored blotches.

There is no magic in it. A pleasing grain just carries more detail in its texture than a smoothed-over digital image, so the eye reads the picture as rich.

What does the ISO number have to do with it?

On film, the ISO number is the speed rating. ISO 100 film is slow and fine. ISO 800 and 3200 are fast and coarse. Wikipedia explains the rating under film speed. The same number appears on a digital camera, where raising ISO raises noise.

In Proofsheet the numbers in look names, such as Frost 100 or Static Mono 3200, are labels for the character of the look. Frost 100 is described as cool, crisp and fine grained, while Static Mono 3200 is heavy grain in black and white. They are not claims about real film stocks.

How do apps fake grain?

There are two common methods. The weak one pastes a grain image over the photo. It looks the same everywhere, and you can often spot the repeat. The better one generates grain per frame and scales it to the picture, with more in the shadows and less in the highlights.

Proofsheet seeds its grain from the roll and the frame number. The same frame comes out identical each time it is rendered, and different frames get different grain. The grain is scaled to the look, so a fine look gets fine grain.

How can I tell good digital grain from bad?

• Zoom into a dark, flat area. Real grain varies across the frame.
• Compare two frames from the same roll. The pattern should differ between them.
• Look at skin. Overdone grain makes faces look dirty.
• Check that the grain size suits the picture size. Huge grain on a small image reads as noise.

Can I remove noise and add grain?

Yes, and photographers do exactly that: clean the sensor noise first, then add grain you control. Doing it the other way round just adds a second layer of texture on top of the first. In a camera app that develops frames later, the app can treat the original frame and the look as separate steps.

Does grain make photos worse?

Only when it hides what the picture is about. A portrait shot in good light holds up under a lot of grain. A distant landscape does not. If the subject is small and detailed, use a fine look. Proofsheet's sample frames in the roll picker show how each look treats a scene before you commit.

For the bigger picture of what a film look is made from, read about film looks and the guide on how to take photos that look like film.

Which one should I worry about when I shoot?

On a phone, worry about noise by finding light. Move toward a window, turn on a lamp or use flash close to the subject. A properly lit frame has little noise to fight, and the look you add later has a clean base.

On film, grain is a choice you make when you buy the roll. If you know you will shoot indoors or at night, take a faster film and accept the texture. Trying to avoid grain in dim light with a slow film gives blur instead.

A short checklist before you add grain

• Is the frame sharp? Grain will not fix blur.
• Is the scene clean in the shadows? Noise from a dark phone shot will clash with added grain.
• Does the picture have a large smooth area such as sky or a wall? Grain shows most there.
• Will it be viewed small? Fine grain disappears on a phone screen, so a slightly stronger look can help.