FlowStacker – A simple tool for stacking photos of moving people.

Photo stacking is used a lot to generate HDR images and increase depth of field in macro photography, but it is also a useful tool for reducing image noise, even without exposure bracketing. Stacking gives better results than traditional noise reduction because it can enhance detail, instead of smearing the image. Being a fan of small and light cameras, I find stacking to be a very useful tool for reducing grain and increasing colour depth when shooting in low light conditions.

Usually, trying to photo stack images of people results in 'ghosting' problems because they just can't keep still long enough so the images don't line up with each other in a simple way. To make things a bit easier, I've put together a simple tool to handle the deformations required to stack photos of people and other moving subjects.  It will handle a moderate amount of movement, but nothing excessive. It's also quite useful for hand-held macro photography without a flash because it can compensate for the parallax effect caused by small movements of the camera.

However, if you are hoping to use it for bracketed HDR, or macro focus stacking, it won't do that.

You will need a 64 bit version of Windows to run it, and you must also install OpenCL (which should come with recent graphics card drivers).

Download FlowStacker from here: FlowStacker

The general idea is to set your camera on burst mode, and high enough ISO to avoid motion blur and shoot a set of around 4 to 16 frames as quickly as possible, then use FlowStacker to combine them to reduce noise, and increase colour depth. It can handle small movements of people while you shoot the burst, and quite large distortions from electronic or rolling shutter. You will get best results from shooting raw, and converting to 16 bit png or tiff without using any noise reduction or compression. The option for extra smoothing can be enabled for high ISO images where the only changes comes from camera movement, such as star photography or static landscapes.

When you open FlowStacker, you will see the main window:

 

Press 'load images' to select the photos you want in the stack.  You can select which of the image is the master that all others will be aligned to.  Press delete on a selected image to remove it.  Set the output image for your stacked result, and hit 'Start Processing'.  Expect processing to take a few minutes, depending on how fast your processor and graphics card are.

Here is an example from a dimly lit restaurant. Even using a wide f/1.4 aperture, I was shooting at ISO 3200 and 1/40th second exposure to avoid camera shake. I was able to fire off 8 shots in burst mode before my subject's reluctant smile had faded.

Each individual raw converted image has clearly visible noise:

After combining the 8 shots in FlowStacker, the result has a much higher quality:

The next one was an attempt to capture a tiny spider hiding in the far reaches of my greenhouse. Getting the shot required holding the camera at arm's length while attempting to keep manual focus while the web was moving gently in the air current. Yes, a flash would be easier, but sometimes inspiration strikes when we are least prepared.

One of 16 original images taken at ISO 6400 and heavily cropped:

After stacking, the image noise is down to a more acceptable level: