Star Stacking Tool
The Star Stacking Tool combines a series of night sky exposures into a single image for astrophotographers and landscape photographers. Select multiple photos shot from a tripod, and it blends them in Maximum mode, keeping the brightest value of every pixel, which builds glowing star trails and brightens a dark frame.
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Frequently asked questions
What does the Star Stacking Tool do?
It merges several photos of the night sky into one image. For every pixel position it compares all your frames and keeps the brightest red, green, and blue values it finds, a method called maximum or lighten stacking. Because the stars move slightly between exposures, their bright points join into trails, while the foreground stays as it is in each frame.
How do I stack star photos?
Click Select Starry Night Photos, or drag and drop, and choose all the exposures from your sequence. They are listed by name and the Stack Images (Maximum Mode) button becomes active. Click it and the button shows Stacking while the frames are combined. When it reads Done, the result has downloaded as stacked-stars.png.
How should I shoot photos for star stacking?
Use a sturdy tripod and do not move the camera between frames, because the tool does not align images. Keep the same focal length, aperture, ISO, and exposure time for the entire sequence, and use an intervalometer or continuous shooting with minimal gaps so trails stay unbroken. Every frame must have the same pixel dimensions, since the stack uses the size of the first image.
Does Maximum mode reduce noise?
No. Maximum mode keeps the brightest value at every pixel, so it is designed for star trails and for gathering light from a sequence, not for noise reduction. Hot pixels, aircraft, and satellite streaks from any single frame will also appear in the result. Remove unwanted frames before stacking, or retouch stray streaks afterward.
How many frames do I need for good star trails?
Trail length depends on the total time your sequence covers, not the number of files. Thirty 30-second exposures cover about 15 minutes and give short arcs, while a few hundred frames over two hours give long, sweeping trails. Point toward the celestial pole for circular trails. Larger sequences take longer to process, since each frame is held in memory.
Is the Star Stacking Tool free and private?
Yes. It is free, adds no watermark, and processes every frame inside your browser, so your photos are never uploaded to a server and there is nothing to install. To use it, you answer that you are a photographer and create or log in to a free Imagen account once, which unlocks all the tools.
