Most of us think of the noise we see in photographs as being related to the photographer using a high ISO when shooting. While that’s the case a good majority of the time, there is another type of noise that can be introduced to images that’s triggered when a photographer uses longer exposure times. Longer exposure times tend to heat up the camera’s sensor and can cause what’s referred to as “amp noise” or “fixed-pattern noise.” This noise can be seen as “bright, abnormally colored flecks of light in an image” and “fog-like brightening around the edges of the frame.” It’s location is generally consistent across photos in a shoot because the same areas of the sensor stay warm while shooting. The noise clings to the warmer areas of the sensor.
If I had to guess, 99% of us really don’t care what type of noise this is or how it’s caused. We just want it to go away. I’ll tell you though, it’s not a bad thing to learn as much about your camera and photography as you can because there may come a time that you need to troubleshoot something. If you once learned about what causes strange color flecks while shooting longer exposures, you might know where to look to solve the problem.
The underlying issue with this very specific type of camera noise is that it’s terribly difficult to remove once the photo has been captured. It doesn’t look like other types of noise and post processing isn’t very good at solving the problem.
What Can Be Done To Remove Long Exposure Noise?
While all of this is definitely a concern for those of us who enjoying shooting with long exposure times, there are surely some steps we can take to mitigate the issue. I’ll list those steps below.
1. Decide which brand of camera to buy. Different camera brands handle long exposure noise differently. Some handle it very well while others are terrible at it. From what I hear right now, Canon isn’t the greatest while Nikon fares very well. I’m hesitant to even write this because various makes, models and technologies are introduced constantly. If you’re looking for a new camera and you know you’ll be taking long exposure shots, be sure to look into this very specific detail. It can save you a lot of pain later on.
2. Let your camera cool between exposures. To be clear, I’m talking about exposure in minutes here, not seconds. If you take one long exposure shot and then take another one directly after it, you’ll likely end up with a lot more noise in the second photo than the first. The reason for this is that the first photo was taken with a cooler camera sensor. To reduce long exposure noise, it’s best to wait a few minutes between photos to give the sensor some time to cool off.
3. Take longer exposure shots in cooler air. Believe it or not, ambient air temperature can have an effect on sensor temperature. If you’re looking to keep the camera temperature down, it only makes sense to take certain types of photos during certain times of the day or during cooler seasons of the year. I know this advice doesn’t help a lot of people out there, but it is something to keep in mind. Or, at the very least, it will help your brain when you’re trying to figure out why some photos taken during the winter aren’t as noisy as others that were taken during the summer.
4. Remove the noise in post-processing. Sometimes, the individual flecks of long exposure noise are so large that you may be able to remove many of them by taking advantage of the healing and spot removal tools in Adobe Camera Raw, Lightroom and Photoshop. Now, I’m not advising that you sit at your computer all day to remove the noise from a photo that you’re only going to post to Facebook, but if you really like a photo and you plan on selling it, perhaps the effort will be worth it.
5. Take advantage of built in Long Exposure Noise Reduction (LENR). Camera makers today are obviously aware of this issue and have done something about it. For many higher-end cameras, there’s an available feature called Long Exposure Noise Reduction that can help remove this type of noise substantially. If you’d like to know if your camera has this option available, you’ll need to take a look at your options under your settings menu.
The whole trick here is to remove the added noise before the user sees it. The way the camera manufacturers have accomplished this is to have the camera take a second photo, right after the first. The second photo doesn’t capture the scene though. Even though the same exact settings are used for both photos, the second photo is captured as if someone has their hand over the end of the lens. No light is allowed in. Because this noise is created by having a warm sensor and because it’s consistent between photos, it’s easy for a camera to compare both the first shot and the second blank shot. The second shot will still contain the noise and after the camera compares the two, it can remove any noise it finds in the second shot from the first. I know this sounds sort of confusing, but it works. I’ve seen tons of photos that have been helped substantially by using this approach. The only time I’ve heard of it not working is during photo shoots that require very high ISO levels. During those instances, other types of noise is introduced and you’ll be dealing with more than what I’m referring to in this post.
The pitfall of using this solution is that it doubles the time it takes to capture a scene. Because the camera needs to essentially take two long exposure photos that take the same exact amount of time each, you may end up doing a lot of waiting around. If time is of the essence, this may not be the option for you. Hopefully some of the above choices will work out.
A Special Trick
As I was studying up on this topic, I did some reading and found a great trick that truly helps with this type of “noisy” situation. Here is is. All you need is Adobe Photoshop. I tried it out and it really does do a fantastic job of removing this very specific type of noise in a photo.
First, open your noisy photograph in Adobe Photoshop. Drag the background layer down to the Create New Layer icon at the bottom of the Layers panel. Doing this will create a duplicate of the that background layer. This duplicate should sit above the background layer in the panel.
Second, click on the duplicate layer in the Layers panel to select it. Then, head up to the Filter > Noise > Median menu item and when the Median dialog box appears, set the radius to 4. Depending on the size of your photo, you may need to go slightly larger or slightly smaller. Experimentation may be necessary. When finished, click on the OK button to apply the noise reduction.
Third, with the same layer still selected, change the blending mode to Pin Light in the Layers panel. What you’ll see after doing this is nothing short of magic. The noise will be (hopefully) gone.
Another Special Trick
I read this extra trick online. Basically, the claim is that if you are on a shoot, go ahead and take one shot at the same exposure time as all the others. For this extra shot though, place the cap on the lens or put your hand over it to make sure absolutely no light gets to the sensor. What you’ll get with this photo is just the noise. As you’re editing in Photoshop later on, you can use this image and place it as a layer on top of whichever real image you’d like to edit. After this, you can change the blending mode of the dark shot to Difference and use the Opacity slider to reduce the level of noise in the photo below. I’ve never tried this, but it seems to be a manual version of what the camera does during its long exposure noise reduction operation, without the added wait time experienced with that process.
I hope I clearly explained how to deal with amp noise in photos as well as the benefits and pitfalls of using the built in long exposure noise reduction feature many cameras offer today. If you have any questions regarding this post, please leave them for me in the comment section below. Thanks for reading!