Can I stack images of different sizes?

No. If any image differs from the baseline (first image) size, the tool refuses to stack. Resize them first with the image-resize tool.

How many frames do I need for astrophotography denoising?

Random noise decreases with the square root of the number of frames: 8 frames roughly cut it by 1/3, 16 by 1/4. Use 8–32 same-exposure shots on a tripod for best results.

How many frames for median?

To erase moving subjects, ensure each subject occupies fewer than half the frames at any given pixel. 5–10 frames work for fast-moving subjects; use 15+ for slower ones.

Star trails: Lighten or Average?

Use Lighten. It keeps the brightest sample at each pixel, so every star position is preserved. Average dilutes the trail.

Median uses a lot of memory.

Median keeps every pixel for every frame in RAM. Large images × many frames can use hundreds of MB. Downscale to ~2K or reduce the frame count if your browser crashes.

Is anything uploaded?

No. Canvas + getImageData runs entirely in your browser.

Back to Image

Image stack — average / median / lighten / darken multiple images

Combine multiple same-size images (JPEG / PNG / WebP) into one PNG by stacking them per-pixel: average for astrophotography noise reduction, median to remove people from a busy scene, maximum (lighten) for star trails or firework composites, minimum (darken) to keep the dark frames. Runs entirely in Canvas + getImageData; your photos never leave your device.

imagemerge

How to use

Drop or pick two or more images. They must all share the same dimensions. Pick a stack mode: Average for denoising, Median for removing moving objects, Lighten for accumulating bright detail (star trails, fireworks), Darken for keeping the dark frames. Click Stack. The browser composites the images per pixel via Canvas. Save the result as PNG (alpha preserved).

FAQ

Can I stack images of different sizes?: No. If any image differs from the baseline (first image) size, the tool refuses to stack. Resize them first with the image-resize tool.
How many frames do I need for astrophotography denoising?: Random noise decreases with the square root of the number of frames: 8 frames roughly cut it by 1/3, 16 by 1/4. Use 8–32 same-exposure shots on a tripod for best results.
How many frames for median?: To erase moving subjects, ensure each subject occupies fewer than half the frames at any given pixel. 5–10 frames work for fast-moving subjects; use 15+ for slower ones.
Star trails: Lighten or Average?: Use Lighten. It keeps the brightest sample at each pixel, so every star position is preserved. Average dilutes the trail.
Median uses a lot of memory.: Median keeps every pixel for every frame in RAM. Large images × many frames can use hundreds of MB. Downscale to ~2K or reduce the frame count if your browser crashes.
Is anything uploaded?: No. Canvas + getImageData runs entirely in your browser.

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