What is Noise Reduction, and is it really necessary?

With late spring's warmer nights, the upcoming new moon cycle, and a visible Milky Way core, now is the perfect time to venture out and capture the incredible beauty in the night sky. However, a common issue for nighttime landscape images is noise in exposures, a byproduct of those higher ISOs and longer shutter speeds required at night. 

Let's dive into a little conversation about noise and nighttime landscape photography. 

Without getting too technical, noise in a landscape photo are grainy-like imperfections that can result in lower image quality. Imperfections can reduce details, cause image discolouration, especially in the shadows, and generally look unpleasant. 

To help mitigate noise using longer shutter speeds and high ISOs, most digital cameras offer a High ISO NR option (noise reduction) and/or Long exposure NR option. These two in-camera options can be selected before image capture. Both options work similarly. The goal is to reduce output noise in your photo. 

When a photographer chooses the High ISO NR, the camera will apply a noise reduction process to the exposure. The drawback is that you have little control over the amount of noise reduction used in the camera, and this application will reduce overall image details. 

When a photographer chooses the Long exposure NR option in the camera, the camera will take two consecutive images, a light frame (the image exposure) immediately followed by another exposure, the dark frame (completely dark). The camera then averages out the pixels in an attempt to remove noise. The drawback of this approach is that, again, the photographer has little control over the outcome of noise reduction. Also, the photographer must wait twice as long as the camera processes the photo. For example, if you've captured a one-minute exposure, you'll wait two minutes if you use in-camera noise reduction. 

Tracked and stacked ISO 1250, 16mm, f4, 180 sec - Sky, Blue hour blend foreground ISO 200, 16.5mm, f9, 30 sec

So the question remains, "What can a photographer do to address digital noise in a nighttime landscape photo?" There are several good options; however, my preferred method for most photographers is stacking. In this situation, a photographer takes several consecutive light frames (10 or more) of the same scene and then several consecutive dark frames (lens cap on - 10 or more) using the same settings. All these images are then imported into a program like Sequator (PC user) or Starry Landscape Stacker (Mac User). These programs reduce noise in a photo by taking the median of the images after outlier elimination which is more effective in addressing noise reduction than the in-camera averaging noise reduction process.  

So next time you're out capturing nighttime landscape images, I highly recommend you try out the technique of stacking. Sequator is free software, and Starry Landscape Stacker offers a free trial! So you have nothing to lose except all that unsightly high ISO and long exposure noise.