Astrophotography Stacking Tool

It performs a mean stack. Every frame you load is read pixel by pixel, and the red, green and blue values at each position are averaged across all frames to produce a single image. Because random sensor noise differs from frame to frame while stars and nebulae stay put, averaging smooths the noise and leaves a cleaner result than any single exposure. The stacked image downloads as a PNG file.

Click the upload area and select all the frames you want to combine at once. Each file appears in a list marked Pending. The Stack Images button becomes active once at least two frames are selected. Click it and the tool loads each frame, marking it Loaded, then averages them and downloads the result as stacked-astro-image.png. Larger and more numerous frames take longer, so give big sets a moment.

No. It combines the pixels that sit at the same position in every frame, so your exposures need to line up already. Frames shot on a well-polar-aligned tracking mount over a short period usually stack cleanly. If your subs have drifted or were taken across a meridian flip, register them in dedicated stacking software first, otherwise stars will appear trailed or doubled in the averaged result.

Use JPG or PNG frames, or any other image format your browser can open. Camera RAW and FITS files are not read, so export them to PNG or high-quality JPG first. All frames should have the same pixel dimensions, because the first frame you select sets the size of the output. The finished stack is saved as a lossless PNG, ready for stretching and editing in your usual software.

More frames give a smoother result, since noise drops roughly with the square root of the number of frames: four frames halve it and sixteen cut it to a quarter. The trade-off is memory, because every frame is held in your browser while it is averaged. Ten to thirty full-size frames work well on most computers. For very long sequences, stack in groups and then stack those results together.

Yes. The tool is free, adds no watermark and needs no software. Stacking happens inside your browser, so your frames are processed on your own device and are never uploaded anywhere. Access requires a one-time step: confirm you are a photographer and create or log into a free Imagen account, which unlocks every tool. Imagen also makes AI editing software that learns your personal editing style.