Photoshop Automation: batch resize & export images for Xcode .xcassets catalogs as @1x, @2x, @3x resolution versions from @3x source images.

ps-batch-ios-assets.jsx

// batch-export-ios-assets.jsx
// Licensed under MIT. See below.
//
// Tested with: macOS 10.15.6, Adobe Photoshop 2020 v21.2.3 Release
//
// Description:
// A JS script that enables simple automated *batch* exporting for
// images in the @1x, @2x, @3x sizes required for Xcode .xcasset catalogs
//
// This script makes a few assumptions, you should either adjust
// your local workflow to meet these, or edit the script before running:
//
// - Your source images are already in 3x resolution
// - Your source images are NOT named @3x, because this script handles that
// - That you are exporting every image in the folder you select as a source
// - That you want the resized files exported using the same name as the original
//
// Preparing your Files:
// - Use your photo processing tool to export your source images at 3x resolution
// Generally, you shouldn't scale up raster images like pngs, because it
// causes quality loss, so export your source file in @3x (don't name it that, just at 3x resolution)
//
// Running this script:
// - Download this gist and unzip it
// - Open the .jsx file with Photoshop (drag it to the PS icon, or right click and "open with" works best)
// - It will prompt you for the folder that contains the assets you want export @1x and @2x versions for
// - It will prompt you to select the output folder
// - Go get coffee, processing time depends on your local machine and you will not be notified when it is done.
//
// This script was adapted for iOS assets from another
// author. Thanks!
// orignal source: https://demosthenes.info/blog/993/1x-2x-3x-more-Batch-Processing-Retina-Images-with-PhotoShop-and-JavaScript
//

var inputFolder = Folder.selectDialog("Select a folder to process"),
outputFolder = Folder.selectDialog("Select a folder for the output files"),
imageSizes = [
    ["512px", "512px", "@3x"],
    ["256px", "256px", "@2x"],
    ["128px", "128px", ""]
],
numImageSizes = imageSizes.length;

if (inputFolder != null && outputFolder != null) {
    var fileList = inputFolder.getFiles(/\.(jpg|jpeg|png|gif)$/i);
    for(var i=0; i<fileList.length; i++) {
        var doc = app.open( fileList[i] );
         for (var j = 0; j < imageSizes.length; j++) {
            // variable assignments
            var currentImageSize = imageSizes[j],
            currentImageWidth = currentImageSize[0],
            currentImageHeight = currentImageSize[1],
            currentImageVersion = currentImageSize[2],
            fullname = doc.name,
            filename = fullname.substr(0, fullname.lastIndexOf('.')) || fullname,
            extension = fullname.split('.').pop(),
            saveOptions = new PNGSaveOptions();

            // image resizing
            doc.resizeImage(currentImageWidth, currentImageHeight);

            // save options
            saveOptions.compression = 0
            saveOptions.interlaced = false
            
            var documentPath = decodeURI(outputFolder) + "/" + filename + "" + currentImageVersion + "." + extension,
            file = new File(documentPath);
            doc.saveAs(file, saveOptions, true, Extension.LOWERCASE);
          }
    doc.close(SaveOptions.DONOTSAVECHANGES);
    }
}

// License: MIT
// Copyright 2020, Gigabitelabs
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal 
// in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
// of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.