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The Best Way to Reduce Noise at Night

Updated: Feb 21, 2021

This is a stitched, multi-row panorama of the Milky Way over a sandstone tower in Chesler Park, Canyonlands National Park, Utah. I shot one row for the land and two rows for the sky. I shot four frames at each camera position. I used Stack Mode>Median to reduce noise in each group of land images. I used RegiStar software to re-align the stars in each group of sky images, then used RegiStar's equivalent of Stack Mode>Median to reduce noise in the sky images. I used Lightroom to stitch together all the completed sky images. Then, as a separate operation, I  stitched all the completed land images together. Finally I blended the sky panorama and land panorama together in Photoshop.

Noise is the great enemy of night photographers. Sure, the noise-reduction sliders in the Detail panel in Lightroom work pretty well, but the result is always a compromise. Noise-reduction software attempts to suppress the high-frequency variation in brightness and color that is unwanted noise while preserving the high-frequency variation in brightness and color that is desirable texture and detail. Inevitably, the more you reduce noise, the more you lose fine detail.

Instead of attempting to smooth out noise, delete it using Photoshop’s Stack Mode>Median. The basic idea is to shoot a series of identical frames and stack them as layers in a Photoshop file. Photoshop can then drill down through the layer stack, comparing the value of each pixel to the value of all the other pixels directly above and below it. Photoshop then chooses the median value—the number in the middle of the range—and displays it.

Here’s a simplified example. Let’s say you shoot four identical images. As Photoshop drills down through the layer stack at a particular point in the scene, it finds four pixels. Three have RGB values averaging out to 100. The fourth has RGB values averaging out to 200. The pixels with an average RGB value of 100 are pixels showing the correct brightness and color. The pixel with an average RGB value of 200 is noise—a random and undesirable variation from the true value you want to capture. The median value of that set of four numbers is 100, so that is the value Photoshop displays. Instead of smoothing out the noise, you’ve removed it.