What’s that NOISE? Part 1
It’s pretty likely that you’ve at least heard about noise in digital photos. I’d also be willing to bet that you’ve got a few images in your archive that are great examples of this artifact, but do you really know what causes it? I would imagine that most of you answered “yes” but how about if I tell you that there are three different types of noise and three different causes…now what’s your answer?
In these two posts I’ll go over the three causes of noise and the three solutions.
Cause #1: High ISO
This is the one that you’ve definitely experienced. We all use high ISO’s when we are forced to shoot in low light situations but still need fast shutter speeds. Even if you don’t use manual exposure, your camera will automatically boost the ISO when shooting on Auto Exposure or using the scene modes.
Here’s something you may not know: when you shoot at a high ISO you’re actually UNDEREXPOSING your image. Seems strange, huh? Your images don’t look underexposed because your camera amplifies the signal after you take the photo to make it look brighter. This isn’t too different from listening to a recording in which someone is speaking very softly; you turn it up to hear it better.
Here’s where the problem starts…your camera’s sensor has a specific amount of noise that is always present but usually the amount of signal (your exposure) is so much greater than this noise that you don’t see it. When you don’t have a lot of signal and your camera amplifies it (turns it up) you are also amplifying the noise as well.
Imagine in that same example of the person speaking softly there is a fan on in the background. The noise of the fan is much more quiet than the person but when you turn the recording up to hear the person better the fan gets louder too. You can easily imagine that if the fan stays on and the person speaks more and more softly the difference between their voice and the fan gets smaller. As their voice gets more quiet it gets closer to the volume of the fan which means it will be harder to distinguish their voice from the noise.
So how does this relate to ISO again? The higher you set your ISO the more you are underexposing your image (less signal) and the more your camera has to turn up the signal. As you underexpose the image more and more you are dropping the level of the signal closer and closer to the level of the noise so when your camera amplifies things the noise becomes as apparent as the signal. That’s why you see more noise in your images as your ISO gets higher.
There are several things you can do to prevent or minimize the appearance of high ISO noise.
#1 Shoot at the lowest ISO you can get away with in every situation. Seems like a no brainer but I see people shooting at ISO’s that are much higher than necessary all the time. Remember to check that setting often.
#2 Turn OFF high ISO noise reduction if you use post processing software. The tiny little computer in your camera attempts to get rid of noise by smearing over it to smooth it out. Unfortunately it also softens details and creates strange artifacts in the process. The processor in your computer combined with post processing software are much better suited to the task of removing high ISO noise, especially if you shoot RAW. Lightroom and Photoshop do a remarkable job of removing ISO related noise. In Lightroom, use the Luminance slider in the Detail Panel to remove High ISO noise. Be careful, if you go too far things will look like they’re made of plastic! Check out Fig 1 and Fig 2 to see what an incredible job you can do with RAW images.
#3 Use your tripod and longer shutter speeds. In situations where you don’t need to freeze subject motion your tripod is your best friend. It will control camera movement during the exposure while your longer shutter speed will give you the right exposure in low light.
#4 Get a new camera! I knew you were looking for a reason to buy a new body so I thought I’d give you permission. Really, I’m kidding, but you should know that all cameras are not created equal and you should know the limits of your camera. Newer cameras, especially those with larger sensors and low megapixel counts perform much better at high ISOs. My Nikon D3s is a great example of a camera that is exceptional at these ISO’s. Look at how well it performs at 6400 ISO (fig 3) and prepare to pick your jaw up off the floor once the noise is removed (fig 4).
In my next post I’ll cover two other types of noise and how to overcome the resulting nastiness.