Combine a series of photos of the same scene into one. Stack night-sky frames into star trails, average a burst to wipe out noise, or take the median of tourist shots so people walking through disappear. Everything is computed in your browser.
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0 frames
Add photos or load the demo frames, then press Stack photos.
Stacking mode
Leave off for star trails from a tripod; turn on for hand-held bursts.
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How to use the Photo Stacking
Add your frames: drop 2 or more photos of the same scene, taken from a tripod or as a steady burst. A demo set of 16 night-sky frames is loaded first.
Choose a mode: Lighten for star trails, Mean for noise reduction, Median to remove moving people, or Comet trails for fading trails.
Exclude bad frames by clicking their thumbnails, and turn on auto-align for hand-held shots.
Press Stack photos and compare the result with a single frame.
Download the stacked image as JPG or PNG.
Stacking modes explained
Mode
Per-pixel rule
Use it for
Frames needed
Lighten
Brightest value of each channel across all frames
Star trails, light painting, fireworks, car light trails
As many as possible (50–300)
Comet trails
Lighten, with the running result dimmed a few percent before each new frame
Star trails that taper like comets
50+
Mean
Sum of all frames ÷ number of frames
Noise reduction, silky water, simulated long exposure
4–64
Median
Middle value after sorting all frames
Removing people, cars and birds; removing hot pixels and satellite trails
At least 5, ideally 10–20
Darken
Darkest value across all frames
Removing headlights and bright moving objects from a scene
5+
Why averaging reduces noise
Random noise is different in every frame while the real scene stays the same. When N frames are averaged, the signal stays the same but the standard deviation of the noise falls to σ ÷ √N, so the signal-to-noise ratio improves by a factor of √N. Four frames give the same noise improvement as a sensor with four times the light-gathering area; going from 16 to 64 frames halves the noise once more. Median stacking reduces noise a little less than the mean (for normally distributed noise it leaves about 25% more noise, roughly 1.25 σ ÷ √N) but completely ignores outliers such as a person, a plane or a hot pixel that appears in only a few frames.
Shooting tips
Star trails: wide lens, manual focus at infinity, ISO 400–1600, 15–30 s exposures shot back to back for 30 minutes or more. The Earth turns 15° per hour, so one hour of frames makes 15° arcs. Point at the celestial pole for circles.
Noise reduction: shoot a burst of 8–16 frames with identical settings; lock exposure and focus.
Removing tourists: use a tripod and shoot 15–20 frames 3–5 seconds apart, so people move to different spots between shots.
Exclude frames with airplane lights, a passing car's headlights or a bumped tripod by clicking their thumbnails before stacking.
Use the 500 Rule Astrophotography Calculator to pick an exposure length that keeps stars as points in each single frame.
Frequently asked questions
What is photo stacking?
Photo stacking combines several photos of the same scene pixel by pixel. Depending on the rule used, it keeps the brightest value (lighten), the darkest (darken), the average (mean) or the middle value (median) of every pixel across all frames. Each rule creates a different effect, from star trails to noise-free images.
How do I make star trails from multiple photos?
Shoot many consecutive exposures from a tripod, for example 100 frames of 20 to 30 seconds with no gap between them. Load them here and choose Lighten. Each star is brighter than the dark sky around it, so keeping the brightest value of every pixel draws its path across the sky as a continuous arc.
How much does mean stacking reduce noise?
Random sensor noise drops by the square root of the number of frames. Averaging 4 frames halves the noise, 16 frames cuts it to a quarter, and 64 frames to an eighth. The scene must not move between frames, so use a tripod or turn on auto-align.
How does median stacking remove people from photos?
If a person stands on a given spot in fewer than half of the frames, the middle value of that pixel comes from the frames where the background is visible, so the person disappears. Take 10 to 20 shots a few seconds apart from a tripod. People who stand still in most frames will remain.
Do my photos need to be aligned?
Yes, stacking assumes every frame shows the scene in the same position. Tripod shots are already aligned. For hand-held bursts turn on auto-align, which corrects small shifts up and down and left and right, but not rotation or zoom. For star trails leave it off, because the stars are supposed to move.
Why are there gaps in my star trails?
Gaps appear when there is a pause between exposures. Use continuous shooting or an intervalometer with an interval just one second longer than the exposure time. The Comet trails mode can also make small gaps less noticeable.
Are my photos uploaded?
No. All frames are read and stacked with JavaScript on your device, so even large sets stay private and nothing is sent to a server.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.