Noise in digital imaging. Is it a problem? Is it part of the art? Should you be concerned? Are there exotic techniques you need to learn to eliminate the noise?
Many of us have been taught to fear noise. So much so that I know people who would pass up a great shot because the image might be noisy. The fear of noise is an irrational, superstitious fear.
This seems most common in the landscape photography community. Conventional wisdom, and the teaching of most instructors, says we should always shoot at the “native” ISO of the camera for lowest noise. That would be ISO 64 for my camera. If we don’t, we are increasing the noise in our images and that would be a “bad thing”.
Have you ever examined the feared noise yourself? Do you understand what it is and what effect it has on prints? Have you confronted the monster and stared it down?
The digital sensor is an amazing piece of technology. It has a HUGE grid of photo-receptive sites. My Z7 has nearly 46 million pixels. A strand of the smallest human hair would cover at least 14 of these pixels. No wonder I see dust spots!
Did you know that “digital” imaging is actually an analog process? Each receptor “adds up” the number of photons it receives for a frame. This is a scalar value, an analog signal. Each site is read out to an amplifier and analog-to-digital converter where it is transformed into a digital value. The amplification is determined by the ISO setting – dialing in a greater sensitivity corresponds to more amplification. This amplification is one source of noise. Any time you take a very low level analog signal and amplify it, some noise is inescapable.
But in addition, the sensor chip itself contributes noise. There is a phenomenon called “shot noise”. It is beyond my ability to explain simply, but electrons spontaneously generate noise. It is usually low level and it is temperature dependent. This is why your camera probably has a long exposure compensation mode. It is there to reduce this background noise accumulated over a long exposure. During a long exposure the sensor is powered for long enough to raise its temperature, leading to increased noise. The compensation mode takes another exposure, but with the shutter closed. This reads the background noise level with no light coming in. The camera basically subtracts the noise signal from the original image. It does a pretty good job.
The amplifier and the sensor noise generation are 2 significant sources of noise in digital imaging. Not the only ones, but they are big. Keep in mind that most of the writers you will see do not have a significant technical background. They sometimes give bad advice because they do not really understand what is happeningl
What does the dreaded noise look like?
Take an image with the ISO cranked up pretty high, say 12,800. Look at it at 1-to-1 magnification in your editing software. You will see that it looks kind of like blotchy sandpaper. You are seeing the 2 primary types of digital noise: luminance noise and color noise.
Luminance noise looks kind of like the grain we used to see in fast black and white film. Some people like it and it does add an interesting texture to some images. Color noise is the mottled color patches you may see at high magnification. I don’t know of anyone who likes that. Both of these types of noise can be compensated for significantly by your editing software, like Lightroom Classic.
Let me point out that noise is just a part of the image capture. It is not something that, when they see it, the authorities kick you out of the gallery or revoke your artist’s certificate. You have an artist’s certificate, right? 🙂
Noise is part of the technology we deal with because we do digital imaging. We need to be aware of it and know how to deal with it, if it is a problem for us. I mentioned amplification noise and sensor noise.
To minimize noise, keep the ISO low, keep the sensor cool, and minimize long exposures. Simple. But what if that doesn’t work?
I will use me as an example. I often shoot in low light, sometimes hand held with no tripod. And I often use long exposures. Am I doomed?
Here are the decisions I generally make: if I want the image to be free from blurring caused by shake, I up the ISO until the shutter speed is at about 3x the focal length. Yes, conventional wisdom is 2x, but I find that does not work well for very high resolution sensors, even with great image stabilization. If I want a long exposure for the creative effect, I use it. Noise is not a significant consideration most of the time. And, unconventionally, I usually leave the long exposure noise compensation off.
Let me address that last one. Why would I leave the long exposure noise compensation off? The noise here is made worse by sensor heating. I shoot a lot in Colorado. Unless it is mid summer, the sensor stays pretty cool. As a matter of fact, it is often more of a problem keeping the battery warm enough to not shut off. And even in summer, it is not a problem to wait a few seconds between shots to let it cool. There have been a few times where I have gotten in trouble with this, but very few.
For me, noise is just a part of the creative balance. Sometimes I want to minimize it, sometimes I actually want to introduce it. Even for the vaunted landscapes, noise can introduce a welcome texture at times, maybe to give a grit for effect or to give subtle interest to a featureless sky.
I do not fear noise. ISO 400 is my default setting – that is 3 stops over the camera native ISO. I do not mind going to 3200 or 6400 if I need to as a tradeoff to capture what I want.
With my camera it is hard to discern noise at 400. There is not much to find at 1600. I admit, my old training to favor the lowest ISO sometimes interferes with my artistic judgment. I try to fight it.
The image with this article was shot at ISO 6400, with what is, as of this writing, an 8 year old sensor. I’m not ashamed of the noise. It I didn’t shoot at 6400 I would not have gotten the image. Good tradeoff, to me.
Noise is a traditional part of photography. It is a feature that sets it apart from painting. Black & White photography favored grain for a gritty look. Many artists like the effect. Even the ones who may not use it recognize and accept it as part of the medium. Digital noise is the equivalent.
So don’t fear noise. Accept it. Use it where you can. Understand where it comes from and what control you have. Your editing tools have ways to reduce it, and they do a pretty good job. Luminence noise is not exactly the same thing as grain, but the overall effect is not that different. Perhaps always totally eliminating noise is not the goal. Did you ever see the slider in LIghtroom Classis in the Effects panel to increase grain? Play with it sometime. It may add to your artistic vision.