Adobe 13102498 - Photoshop CS3 - Mac User Manual page 602

Image stacks are stored as Smart Objects. The processing options you can apply to the stack are called stack modes.
Applying a stack mode to an image stack is a non-destructive edit. You can change stack modes to produce different
effects; the original image information in the stack remains unchanged. To preserve changes after you apply the stack
mode, save the result as a new image, or rasterize the Smart Object. You can create an image stack manually or using
a script.
Creating an image stack (Photoshop Extended)
For best results, images contained in an image stack should have the same dimensions and mostly similar content,
such as a set of still images taken from a fixed viewpoint, or a series of frames from a stationary video camera. The
content of your images should be similar enough to allow you to register or align them to other images in the set.
Combine the separate images into one multi-layered image. See "Duplicate layers" on page 281.
1
Note: An image stack must contain at least two layers.
You can also combine images using a script (File > Scripts > Load Files into Stack).
Choose Select > All Layers.
2
Note: To make the Background layer selectable with the All Layers command, you must first convert it to a regular layer.
3 Choose Edit > Auto-Align Layers and select Auto as the alignment option. If Auto does not create good regis-
tration of your layers, try the Reposition option.
Choose Layer > Smart Objects > Convert to Smart Object.
4
5 Choose Layer > Smart Objects > Stack Mode and select a stack mode from the submenu.
• For noise reduction, use the Mean or Median plug-ins.
• For removing objects from the image, use the Median plug-in.
The output is a composite image the same size as the original image stack. You may need to experiment with different
plug-ins to get the best enhancement for a particular image.
To change the rendering effect, choose a different Stack Mode from the submenu. Stack rendering is not
cumulative—each render effect operates on the original image data in the stack and replaces previous effects.
Stack modes
Stack modes operate on a per-channel basis only, and only on non-transparent pixels. For example, the Maximum
mode returns the maximum red, green, and blue channel values for a pixel cross-section and merges those into one
composite pixel value in the rendered image.
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