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Note:
In Photoshop CS6, 3D functionality is part of Photoshop Extended. All features in Photoshop Extended are part of Photoshop. Photoshop does not have a separate Extended offering.
An image stack combines a group of images with a similar frame of reference, but differences of quality or content across the set. Once combined in a stack, you can process the multiple images to produce a composite view that eliminates unwanted content or noise.
You can use image stacks to enhance images in number of ways:
To reduce image noise and distortion in forensic, medical, or astrophotographic images.
To remove unwanted or accidental objects from a series of stationary photos or a series of video frames. For example, you want to remove a figure walking through an image, or remove a car passing in front of the main subject matter.
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.
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.
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Combine the separate images into one multi-layered image. See Duplicate layers.
Note:
An image stack must contain at least two layers.
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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 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 them into one composite pixel value in the rendered image.
Rendering plug-in name |
Result |
Comments |
|---|---|---|
Entropy |
entropy = - sum( (probability of value) * log2( probability of value) ) Probability of value = (number of occurrences of value) / (total number of non-transparent pixels) |
The binary entropy (or zero order entropy) defines a lower bound on how many bits would be necessary to losslessly encode the information in a set. |
Kurtosis |
kurtosis = ( sum( (value - mean)4 ) over non-transparent pixels ) / ( ( number of non-transparent pixels - 1 ) * (standard deviation)4 ). |
A measure of peakedness or flatness compared to a normal distribution. The kurtosis for a standard normal distribution is 3.0. Kurtosis greater than 3 indicates a peaked distribution, and kurtosis less than 3 indicates a flat distribution (compared to a normal distribution). |
Maximum |
The maximum channel values for all non-transparent pixels |
|
Mean |
The mean channel values for all non-transparent pixels |
Effective for noise reduction |
Median |
The median channel values for all non-transparent pixels |
Effective for noise reduction and removal of unwanted content from the image |
Minimum |
The minimum channel values for all non-transparent pixels |
|
Range |
Maximum minus the minimum of the non-transparent pixel values |
|
Skewness |
skewness = (sum( (value - mean)3 ) over non-transparent pixels ) / ( ( number of non-transparent pixels - 1 ) * (standard deviation)3 ) |
Skewness is a measure of symmetry or asymmetry around the statistical mean |
Standard Deviation |
standard deviation = Square Root(variance) |
|
Summation |
The sum channel values for all non-transparent pixels |
|
Variance |
variance = (sum( (value-mean)2 ) over non-transparent pixels ) / ( number of non-transparent pixels - 1) |
Because an image stack is a Smart Object, you can edit the original images that make up the stack layers at any time.
To preserve rendering effects on an image stack, convert the Smart Object to a regular layer. (You can copy the Smart Object before converting, in case you want to later re‑render the image stack.)
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