Median Rendering

Median Rendering In this case involved filming a crowded scene to demonstrate how to make unwanted crowds disappear

If only the crowd I was filming in a casual manner and discreet, only knew that the purpose of the exercise was to make them disappear, some of them were getting quite anxious about a  camera pointed in there general direction, and giving me a nasty look straight through the lens, most unnerving,

maybe I should have wore a sign saying "I'm Photographing You , to make you disappear

Camera was set up at Civic Park in Newcastle NSW, ( On a rainy Day) and was taking photographs of Newcastle Library, The one that used to be hidden by our beautiful Figs that were cut down,

 also managing to capture crowds that walked by to eliminate them later in post production by a very clever and simple means in photo shop however in does take lots of images for the to work

the process involves a technique called Image Stacking

 

IMAGE STACKING

 

Create an image stack

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

1. Combine the separate images into one multi-layered image.

An image stack must contain at least two layers.

You can also combine images using a script (File > Scripts > Load Files into Stack).

2. Choose Select > All Layers.

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 registration of your layers, try the Reposition option.

4. Choose Layer > Smart Objects > Convert to Smart Object.

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.

 

Median is just one of the plug ins that achieve a certain task, upon researcrch here is a list of what tasks do exactly after being converted to Smart Object

 

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 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)

You can use the Statistics script to automate creating and rendering an image stack.

1.Choose File > Scripts > Statistics.

2.Choose a stack mode from the Choose Stack Mode menu.

3.Apply the stack mode to currently open files, or browse to select a folder or individual files.

Files you select are listed in the dialog box.

4.If desired, select Attempt To Automatically Align Source Images (equivalent to choosing Edit > Auto-Align Layers). Then click OK.

Photoshop combines the multiple images into a single multilayered image, converts the layers into a Smart Object, and applies the selected stack mode.

Just some useful added information added to you on your toes

Here are some of the shots with crowd  show below

 

 

 

 

 

 

As you can see the crowd has disappeared that were walking past, the To remaining people sitting down in the park demonstrates that , becasuse these people were not moving  they have remained in photo