透過を含んだ写真画像を、PNGではなくJPEG+マスクPNGにすることで軽量化するテクニックの補助用にPSDスクリプト書いてみた。

ExportWithSelectionMask.jsx

// Export JPEG for WEB with Selection Mask (as PNG)
// Written by ku-suke <gachasan@gmail.com>

var flag = confirm("Export Selection to PNG.Export original to JPEG.");

if(flag){
	var docObj = activeDocument;
	var baseName = docObj.name.substring(0,String(docObj.name).length - 4 );
	var folderPath = docObj.path + "/" + baseName;
	var folderObj = new Folder(folderPath);
	folderObj.create();
	
	// Save Original JPEG Image
	var exp = new ExportOptionsSaveForWeb();
	exp.format = SaveDocumentType.JPEG;
	exp.quality = 80;					///////// Fixed Value. You can change quality.
	var imgFile = new File(folderPath + "/" + baseName + ".jpg");
	docObj.exportDocument(imgFile, ExportType.SAVEFORWEB, exp);
	
	// Save Selection mask to PNG
	activeDocument.channels.add();
	var fillColor = new SolidColor();
	fillColor.gray.gray = 0;
	activeDocument.selection.fill(fillColor);
	activeDocument.selection.selectAll();
	activeDocument.activeLayer.copy();
	
	/* アルファチャンネルを生成後新規レイヤーにコピペ */
	var tempLayer = activeDocument.artLayers.add();
	activeDocument.paste(false);
	tempLayer.name = "Generated mask image";
	exp.format = SaveDocumentType.PNG;
	var maskFile = new File(folderPath + "/" + baseName + "_mask.png");
	docObj.exportDocument(maskFile, ExportType.SAVEFORWEB, exp);

	alert("Saved:\n"+folderPath);
}