merge.jsx

/*
Image Averaging Photoshop Script

Orginal script written by Neil Farquharson | www.verdantvista.com
Augmented by Garry George | www.photography.grayheron.net

Version 1.0.0
Date April 2018

Installation
------------------------
Copy into your scripts folder in Photoshop

Usage
------------------------
Load your frames to be image averaged into a single photoshop document. E.G. if you have 5 frames, they should be stacked in one document as 5 seperate layers.
At the prompt enter a number typically between 2 and 10: note the script does NOT test the input. Select NO to the merge request in this first pass.
Leave the default 100 for normal use, ie a single block, which you can merge if you wish.
After the first pass you will have clearly deleneated blocks of variable opacity: merge each block manually by selecting them.
These merged blocks can then be reprocessed with the script to a single layer, ie YES to merge request.
*/


if (documents.length == 0) 
{
  alert("There are no documents open.");
} 
else
{
  var myDoc = activeDocument;
  var layerRef = myDoc.activeLayer;
  var myLayerCount = myDoc.layers.length-1;
  var blockNum = 1;
    
  if (myDoc.layers.length == 1 && layerRef.isBackgroundLayer == true)
  {
    alert("The Background layer cannot be hidden when it's the only layer in a document.");
  } 
  else 
  {

    numLayers = 1;
    numLayers = Number(prompt("Number = ?","100","Number of layers per block?"));
    
    for (var myCounter = myLayerCount; myCounter >= 0; myCounter--) 
    {
      var myLayer = myDoc.layers[myLayerCount - myCounter]
      var o = 0;
      o = getImageAverageOpacity(myCounter);
      myLayer.name = "Block " + blockNum;
      myLayer.opacity = o;
      if (o == 100) {blockNum = blockNum + 1};
    }
    if (confirm("Do you want to merge the visible layers now?"))
    myDoc.mergeVisibleLayers();
  }
}

function getImageAverageOpacity(LayerNum) {
    var temp = LayerNum % numLayers;
    var newOpacity = 100 * ( 1 / (1 + temp));
    return newOpacity;
}