What Is Noise In Photography? How To Avoid Noisy Photos

Noise is can be a confusing topic for photographers, even some intermediate photographers don’t fully understand what it is or where it comes from. Avoiding noise requires a fundamental understanding of what it is.

The term “noise” in photography refers to digital imperfections that are introduced into an image. Two key sources of noise in photography are shot noise and digital noise. To avoid noise in your photos, you should ensure your photos are adequately exposed and shoot on a low ISO.

Keep reading as I explain what noise is, how it differs from grain, and how to avoid it in your images.

What Is Noise In Photography?

The term “noise” in photography refers to digital imperfections that are introduced into an image. Two key sources of noise in photography are shot noise and digital noise.

Shot noise is a complex topic. A simple way to look at shot noise is that has to do with randomness in the collection of photons. Put simply, more signal means less shot noise. In photography, light is the signal being recorded, so the more exposed your image is, the less shot noise will be present.

Digital noise is introduced by the components that make up your camera. The most notable source of digital noise relates to ISO. Raising your ISO will brighten the exposure of your image, but it will also introduce more digital noise to your image. It is important to note that the amount of noise added varies per camera.

When it comes to noise, it is often thought that more noise is bad. This is not always the case. More digital noise is going to add artifacts to your image and worsen your image quality. With shot noise, on the other hand, there is one key idea to be considered: signal-to-noise ratio.

Signal-To-Noise Ratio

The signal is the information being recorded with light being the signal for photography. The signal-to-noise ratio is just as it sounds. It is the ratio of the signal, in this case, light, to noise in your image.

As your signal or light, increases, your shot noise will also increase, only at a slower rate. This means that shot noise is really only an issue when your signal is low; in other words, to avoid shot noise being an issue you increase exposure.

Shot noise has to do with randomness in the collection of photons. Since they are quantum particles, photons can only be collected in whole numbers. This means that if you sampled the number of photons collected from an unchanging source at random but consistent intervals, you are highly unlikely to get consistent numbers.

For example, let’s say you take random samples of photons at 15-second intervals. Other than when you take these samples, all other factors are fixed such as the source of the photons, your method of capturing data, etc.

If the first sample consists of 10 photons it is highly unlikely the next sample will also have 10 photons. It may have 13, the next may have 9, and so on. The variability in photons between samples is the shot noise.

Interestingly, if you were to plot the data from these random samples, the data points would follow the Poisson distribution. The Poisson distribution is used when you are interested in the probabilities of the number of times an event occurs in a given area of opportunity.

An area of opportunity, in this case, is the amount of time in which more than one occurrence of an event (the presence of photons) can occur. So, in terms of shot noise, the Poisson distribution relates to the probabilities of the number of photons present in our 15-second intervals.

As the number of observations grows in a Poisson distribution, it approaches the normal distribution. What does this mean? The amount of shot noise in an image is a function of the amount of signal or, in our case, light.

As defined by the formula above, the more signal, the more shot noise. Though the shot noise increases at a slower rate, so as the signal increases, the signal-to-noise ratio goes down.

How does this apply to photography? If you have a low amount of signal and try to amplify it, you will also amplify your shot noise. In other words, if you underexpose an image and try to increase the exposure while editing, you will have more shot noise than if you had exposed your image properly in the first place.

What is The Difference Between Noise And Grain?

A common point of confusion for beginner photographers is the difference between noise and grain. As they’re both artifacts added to your image, they do seem similar but are actually quite different.

As we have come to know, noise is made up of imperfections introduced to your image digitally. Too much noise will worsen your image quality and is generally seen as undesirable by photographers.

Grain, on the other hand, is widely used by photographers. It adds texture to your images and helps emulate the same cinematic effect that movies shot on film have.

Grain comes from film photography, a type of photography that has been growing back into its popularity recently. When shooting on film, there are tiny particles on the actual film strip that, when developed, show up in your final image.

The actual grain present differs between film stock, but nowadays it is usually added digitally. Editing software usually has the ability to add grain to your shot, and even control how that grain looks. The type and amount of grain added are subjective and up to the individual photographer.

The photo at the start of this section is a great example of noise versus grain. The noisy image has no noise reduction and no grain added, while the grain image has some noise reduction (added in Adobe Lightroom and Exposure X7) and grain (added in Exposure X7).

We can see the noisy image looks blocky and somewhat pixelated. There is also a subtle horizontal banding in the noisy image. The grainy image, on the other hand, has a nice texture to it that is subtle and not distracting. The differences are easiest to see on the subject’s face but are also noticeable on the solid background.

How To Avoid Noise While Shooting

While editing tools can be useful for reducing noise, it’s best to have the least amount of noise in your image at its source as possible. To do this, there are two things to keep in mind; expose your shot properly and use the lowest ISO possible while doing so.

It’s important to understand that any under-exposed or over-exposed parts of your image cannot be recovered after the shot is taken. With this in mind, “exposing properly” means capturing all the detail you want using the proper exposure.

If you aim to avoid noise in your final image, you should increase your signal, and your exposure, while shooting. This will reduce the signal-to-noise ratio, allowing you to adjust your exposure while editing without ending up with noisy images, but more on that in the next section.

To adjust your exposure in-camera you can raise your ISO, but that will add digital noise. This means you’ll have to rely on your aperture and shutter speed primarily. Opening your aperture wider will allow more light to hit your sensor, increasing exposure, but will cause less area to be in focus.

Using a slower shutter speed will also increase your exposure, the catch is that it will cause motion blur if your subject or light source is moving. Using a tripod can help avoid camera shake being an issue, but won’t completely avoid motion blur.

Another option to help you expose your images well is to use a camera flash. These can be used either on or off your camera body to light your subject or even the entire scene. If you do end up using a flash, I recommend using a diffuser.

A diffuser serves the same purpose in lighting as clouds do for the sun. The light is scattered making it softer and more even. You may hear photographers talk about “softboxes”, these are large diffusers that are put over studio lights.

One final option to help you expose your images is to use “exposure bracketing”. This is the process of taking multiple images at different exposures and combining them in editing software. The purpose of exposure bracketing is to retain as much information as possible.

Under-exposed images retain detail in the highlights, overexposed images retain detail in the shadows. Combining all of these photos allows you to take the best parts of each of them to create one HDR (high dynamic range) image.

How To Reduce Noise While Editing

As a photographer, it is up to you what you want to shoot and how you are going to adjust your settings to shoot it. There will be times when your images are under-exposed, overexposed, or perfectly exposed but high in digital noise.

Among other things, editing software can be used to help change the brightness levels of your images. In software like Adobe Lightroom, be careful with your exposure slider. The exposure slider does not work the same as exposing your image in a camera; it doesn’t increase your signal, it amplifies it.

What’s the difference between increasing and amplifying your signal? You can only increase your signal while shooting. While editing, the information your camera collected to form an image is set. moving the exposure slider doesn’t add any information; it does not increase the amount of signal you have, it only amplifies the existing signal.

How does this apply practically? If you underexpose an image too much while shooting, there will be sections of your image that are completely black with no information. This means raising your exposure slider will reveal shot noise in your image (remember the signal-to-noise ratio is higher when signal is low) and those black spots will not reveal any detail.

On the flip side, if you overexpose your image too much while shooting, there will be white spots with no information. Lowering your exposure slider will only turn those white spots grey, and will not reveal any detail in your image.

Using your ISO is a great way to avoid both of these problems while being able to use your aperture and shutter speed creatively. The only issue, as stated before, is that you will introduce digital noise. Though editing software can get rid of this noise, there are some side effects.

Using Adobe Lightroom as an example, if you overuse noise reduction, your image will come out artificially smooth and somewhat plasticky. That’s not to say noise reduction isn’t a powerful tool, because, when used properly, it is perfect for carving out some space to add stylistic grain to your image.