Script or Batch tutorial on how to copy alpha channel from one set of images to another?

@TorQueMoD2 

I tested the following script based on the single set of 2 images that you have provided. Both source and target images should be in separate folders. The expectation is that both the source and target images are alphabetically sorted in the same order. The PNG quality level can be set via the saveOptions.compression line. You will be prompted for a new location to save to. The output will be PNG. Test with a small set of images to save time (not 3K).

You may wish to split up the 3K files into smaller batches of say 1K if you are happy with the tests. Photoshop can have problems processing large batches of images.

/*
Mask PNG Images with PNG Masks from 2 Separate Input Folders.jsx
v1.0 - 4th November 2023, Stephen Marsh
https://community.adobe.com/t5/photoshop-ecosystem-discussions/script-or-batch-tutorial-on-how-to-copy-alpha-channel-from-one-set-of-images-to-another/td-p/14205993
Based on:
https://community.adobe.com/t5/photoshop-ecosystem-discussions/is-there-a-script-to-apply-a-series-of-alpha-channels-in-bulk-to-a-series-of-images/td-p/13642975
*/

#target photoshop

(function () {

    if (app.documents.length === 0) {

        try {

            // Image input folder
            var folder1 = Folder.selectDialog("Select the target/image folder:");
            if (folder1 === null) {
                //alert('Script cancelled!');
                return;
            }

            // Mask input folder
            var folder2 = Folder.selectDialog("Select the source/mask folder:");
            if (folder2 === null) {
                //alert('Script cancelled!');
                return;
            }

            // Validate input folder selection
            var validateInputDir = (folder1.fsName === folder2.fsName);
            if (validateInputDir === true) {
                alert("Script cancelled as both the input folders are the same!");
                return;
            }

            // Limit the file input to PNG, case insensitive
            var list1 = folder1.getFiles(/\.(png)$/i);
            var list2 = folder2.getFiles(/\.(png)$/i);

            // Alpha-numeric sort
            list1.sort();
            list2.sort();

            // Validate that folder 1 & 2 lists are not empty 
            var validateEmptyList = (list1.length > 0 && list2.length > 0);
            if (validateEmptyList === false) {
                alert("Script cancelled as one of the input folders is empty!");
                return;
            }

            // Validate that the item count in folder 1 & 2 matches
            var validateListLength = (list1.length === list2.length);
            if (validateListLength === false) {
                alert("Script cancelled as the input folders don't have equal quantities of images!");
                return;
            }

            // Output folder
            var saveFolder = Folder.selectDialog("Please select the folder to save to...");
            if (saveFolder === null) {
                //alert('Script cancelled!');
                return;
            }

            // Save and set the dialog display settings
            var savedDisplayDialogs = app.displayDialogs;
            app.displayDialogs = DialogModes.NO;

            // PNG save options
            var saveOptions = new PNGSaveOptions();
            saveOptions.compression = 0; // compression value: 0-9
            saveOptions.interlaced = false;

            // Set the file processing counter
            var fileCounter = 0;

            // Perform the stacking and saving
            for (var i = 0; i < list1.length; i++) {
                // Open the image and get the name
                var doc = open(list1[i]);
                var docName = doc.name.replace(/\.[^\.]+$/, '');
                // Place the mask as a layer
                placeFile(list2[i], 100);
                // Load the mask RGB channel as a selection
                channelSelection();
                // Remove the mask layer
                activeDocument.activeLayer.remove();
                // Add a layer mask from the selection to the image
                maskSelection("revealSelection");
                // Rename layer to image doc name
                activeDocument.activeLayer.name = docName;
                // Save and close the PNG version
                var savePNG = new File(new File(saveFolder + '/' + docName + '.png'), saveOptions);
                doc.saveAs(savePNG, saveOptions, true, Extension.LOWERCASE);
                doc.close(SaveOptions.DONOTSAVECHANGES);
                // Increment the file processing counter for each file processed
                fileCounter++;
            }

            // End of script
            app.displayDialogs = savedDisplayDialogs;
            app.beep();
            alert('Script completed!' + '\r' + fileCounter + ' masked PNG files of ' + list1.length + ' input files saved to:' + '\r' + saveFolder.fsName);

        } catch (e) {
            alert("Error!" + "\r" + e + ' ' + e.line);
        }

    } else {
        alert('Please close all open documents before running this script!');
    }


    ///// Functions /////

    function placeFile(file, scale) {
        try {
            var idPlc = charIDToTypeID("Plc ");
            var desc2 = new ActionDescriptor();
            var idnull = charIDToTypeID("null");
            desc2.putPath(idnull, new File(file));
            var idFTcs = charIDToTypeID("FTcs");
            var idQCSt = charIDToTypeID("QCSt");
            var idQcsa = charIDToTypeID("Qcsa");
            desc2.putEnumerated(idFTcs, idQCSt, idQcsa);
            var idOfst = charIDToTypeID("Ofst");
            var desc3 = new ActionDescriptor();
            var idHrzn = charIDToTypeID("Hrzn");
            var idPxl = charIDToTypeID("#Pxl");
            desc3.putUnitDouble(idHrzn, idPxl, 0.000000);
            var idVrtc = charIDToTypeID("Vrtc");
            var idPxl = charIDToTypeID("#Pxl");
            desc3.putUnitDouble(idVrtc, idPxl, 0.000000);
            var idOfst = charIDToTypeID("Ofst");
            desc2.putObject(idOfst, idOfst, desc3);
            var idWdth = charIDToTypeID("Wdth");
            var idPrc = charIDToTypeID("#Prc");
            desc2.putUnitDouble(idWdth, idPrc, scale);
            var idHght = charIDToTypeID("Hght");
            var idPrc = charIDToTypeID("#Prc");
            desc2.putUnitDouble(idHght, idPrc, scale);
            var idAntA = charIDToTypeID("AntA");
            desc2.putBoolean(idAntA, true);
            executeAction(idPlc, desc2, DialogModes.NO);
        } catch (e) {}
    }

    function channelSelection() {
        var s2t = function (s) {
            return app.stringIDToTypeID(s);
        };
        var descriptor = new ActionDescriptor();
        var reference = new ActionReference();
        var reference2 = new ActionReference();
        reference.putProperty(s2t("channel"), s2t("selection"));
        descriptor.putReference(s2t("null"), reference);
        reference2.putEnumerated(s2t("channel"), s2t("channel"), s2t("grain"));
        descriptor.putReference(s2t("to"), reference2);
        executeAction(s2t("set"), descriptor, DialogModes.NO);
    }

    function maskSelection(maskParameter) {
        // Parameter = "revealSelection" or "hideSelection"
        var s2t = function (s) {
            return app.stringIDToTypeID(s);
        };
        var descriptor = new ActionDescriptor();
        var reference = new ActionReference();
        descriptor.putClass(s2t("new"), s2t("channel"));
        reference.putEnumerated(s2t("channel"), s2t("channel"), s2t("mask"));
        descriptor.putReference(s2t("at"), reference);
        descriptor.putEnumerated(s2t("using"), s2t("userMaskEnabled"), s2t(maskParameter));
        executeAction(s2t("make"), descriptor, DialogModes.NO);
    }

}());

https://prepression.blogspot.com/2017/11/downloading-and-installing-adobe-scripts.html