Can burst-shot image stacking reduce noise without a tripod, and what software can do it?

Question

I’d like to reduce noise by shooting a burst of many identical frames and merging them, similar to what apps like Cortex Camera do. This is not HDR or exposure bracketing. My goal is to hand-hold a low-light scene, capture a short burst, and combine the images to get a cleaner final photo.

I use a Sony NEX and a Mac. I have Lightroom but not Photoshop, and I’d prefer either a standalone Mac app or a Lightroom-compatible tool. Ideally the workflow would be simple: load images, align them automatically, merge, and save. The software needs to tolerate small shifts and slight rotation between frames, since I do not want to rely on a tripod or remote release.

Is this technique practical, what is it called, and what kind of software should I look for?

user15871 · Accepted Answer

The technique used by Cortex Camera is called Median Blending. Astrophotographers have been using this concept for years to combine multiple photos of dim objects in the night sky to reduce the noise and increase contrast and color. It is often referred to as image stacking in which hundreds of images of the same piece of sky are overlaid and the values for each pixel are set at the median value for that pixel from all of the combined images. But astrophotography is far from the only type of imaging that benefits from Median Blending.

Most full featured imaging applications, such as Photoshop and the GIMP, include the ability to do image stacking. There are also some cameras such as the Sony A-mount and E-mount cameras that can do this in-camera. Depending on exactly which model NEX you have, your camera may already include this feature. It is called Twilight Handheld Mode. The camera captures a series of photos in rapid succession (maybe 5 photos) and then merges them to create a low-noise JPEG. As with anything done in-camera, you give up the finer control of a post-processing application for the convenience and time savings of letting the camera make many decisions for you.

Although it works fairly well without a tripod, for the ultimate in resolution you will still want to stabilize the camera. When the camera moves slightly from one frame to the next, then everything in the image will shift a certain number of pixels. If the shift is purely horizontal and/or vertical, there isn't much loss in terms of absolute resolution. This is rarely the case. When the shift from one photo to the next is diagonal, or worse yet rotational, then there is not a one-to-one correspondence of pixels from one frame to the next. The use of a Bayer filter to mask different pixels with different colors also comes into play when the camera shifts between exposure. This reduces the effectiveness of using the median value of each pixel by a miniscule amount in much the same way that using a lens correction profile to correct the distortion created by a lens' design will reduce the absolute resolution of an image.

Here are some links to articles and discussions on the subject:
http://petapixel.com/2013/05/29/a-look-at-reducing-noise-in-photographs-using-median-blending/
An expanded version of the same article:
http://blog.patdavid.net/2013/05/noise-removal-in-photos-with-median_6.html
http://www.digitalphotopro.com/technique/revolution/reduce-noise-with-multiple-shots.html
http://diglloyd.com/articles/LensAndCameraIssues/NoiseAndMultipleExposures.html
http://www.cambridgeincolour.com/tutorials/image-averaging-noise.htm
http://photography-on-the.net/forum/showthread.php?t=1221282

Can burst-shot image stacking reduce noise without a tripod, and what software can do it?

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