Non-destructive image stacks blend together a series of images based on the same scene or almost identical subject matter. Visual differences between images in the series can then be removed, composited together, or used for creative effects.
About image stacks
Use image stacks for:
Exposure merging: Merging images of varying exposures.
Object Removal: Use a series of images to blend out unwanted subject matter from a specific image in an image set.
Noise reduction: Blend together multiple shots of the same subject and average out the noise.
Creative effects: Simulate long exposure imagery and combine bright subjects (e.g., fireworks) for a composite effect.
About stack operators
A choice of operators can be applied to your stack depending on what you want to achieve. Median can be used for most blending operations such as object removal, exposure merging (exposure blending) and noise reduction.
To create a stack:
From the File menu, select New Stack.
From the dialog, click Add to locate and select your images for blending. Click Open to add the images to the stack list.
(Optional) Uncheck Automatically Align Images to manually align images later in the Layers panel.
Choose a Perspective or Scaling operation from the menu to allow for successful auto-alignment. The former applies a perspective adjustment to each image; the latter repositions and/or sizes the image layer.
Check Live Alignment to add a live perspective filter to each pixel layer in the stack; this allows the perspective of any layer to be adjusted after stacking without affecting its pixel layer (this may affect performance depending on size and number of images to be stacked). Select the layer's perspective filter layer and adjust corner handles on the page.
Your images are blended and presented in a Live Stack Group in the Layers panel. You can manually align layers if auto-alignment isn't 100% accurate.
To change stack operator:
On the Layers panel, click the Stack operator icon on the Live Stack Group. The default operator is Median as indicated by the icon.
From the pop-up menu, select a stack operator suited to the type of photos you are stacking (see above). The icon will change depending on the operator selected.