Start with a 1000x1000 PSD with an icon in the middle. In Photoshop select File > Scripts > Browse... generateSplash.js. Saves out to ../Resources/iphone and android.

generateSplash.js

/*
 Define our various sizes.
 */
var AndroidSizes = {
		'android/images/res-ldpi/splash.9.png': 240,
		'android/images/res-mdpi/splash.9.png': 360,
		'android/images/res-hdpi/splash.9.png': 480,
		'android/images/res-xhdpi/splash.9.png': 720,
		'android/images/res-xxhdpi/splash.9.png': 960,
		'android/images/res-xxxhdpi/splash.9.png': 1440
	},
	iOSSizes = {
		'iphone/Default@2x.png': { width: 640, height: 960 },
		'iphone/Default-568h@2x.png': { width: 640, height: 1136 },
		'iphone/Default-667h@2x.png': { width: 750, height: 1334 },
		'iphone/Default-Landscape-736h@3x.png': { width: 2208, height: 1242 },
		'iphone/Default-Portrait-736h@3x.png': { width: 1242, height: 2208 },
		'iphone/Default-Landscape.png': { width: 1024, height: 768 },
		'iphone/Default-Portrait.png': { width: 768, height: 1024 },
		'iphone/Default-Landscape@2x.png': { width: 2048, height: 1536 },
		'iphone/Default-Portrait@2x.png': { width: 1536, height: 2048 }
	};

/*
 Utility functions.
 */
var originalPath = app.activeDocument.path;

var black = new SolidColor();
black.rgb.red = 0;
black.rgb.green = 0;
black.rgb.blue = 0;

function save(doc, name) {
	var options = new ExportOptionsSaveForWeb();
	options.quality = 70;
	options.format = SaveDocumentType.PNG;
	options.PNG8 = false; // PNG-24
	options.optimized = true;
	doc.exportDocument(File(originalPath + '/../Resources/' + name), ExportType.SAVEFORWEB, options);
	return options;
}

function dot(doc, x, y) {
	doc.selection.select([
		[x, y], [x + 1, y], [x + 1, y + 1], [x, y + 1]
	]);
	doc.selection.fill(black);
}

/*
 Let's get to it!
 */
(function() {
	var doc = app.activeDocument.duplicate(),
		originalWidth = doc.width,
		originalHeight = doc.height;

	/*
	 Generate iOS splash screens.
	 */
	for (var iOSName in iOSSizes) {
		var width = iOSSizes[iOSName].width,
			height = iOSSizes[iOSName].height,
			least = Math.min(width, height);

		// Scale.
		doc.resizeImage(UnitValue(least, 'px'), UnitValue(least, 'px'));

		// Canvas to the proper size.
		doc.resizeCanvas(UnitValue(width, 'px'), UnitValue(height, 'px'), AnchorPosition.MIDDLECENTER);

		// Save the image.
		save(doc, iOSName);

		// Canvas back to our original aspect ratio.
		doc.resizeCanvas(UnitValue(least, 'px'), UnitValue(least, 'px'), AnchorPosition.MIDDLECENTER);

		// Reverse back to the original.
		doc.resizeImage(originalWidth, originalHeight);
	}

	/*
	 Generate Android .9 patch splash screens.
	 */
	for (var androidName in AndroidSizes) {
		var dim = AndroidSizes[androidName],
			unitValue = UnitValue(dim, 'px');

		// Crop the edges.
		doc.crop([0, 0, originalWidth, originalHeight]);

		// Resize and add a 1px gutter along the whole image.
		doc.resizeImage(unitValue, unitValue);
		doc.resizeCanvas(UnitValue(dim + 2, 'px'), UnitValue(dim + 2, 'px'), AnchorPosition.MIDDLECENTER);

		// Draw dots.
		var newLayer = doc.artLayers.add();
		newLayer.name = '.9';
		dot(doc, 2, 0);
		dot(doc, 0, 2);
		dot(doc, dim - 2, 0);
		dot(doc, 0, dim - 2);

		save(doc, androidName);

		// Undo our changes.
		doc.resizeCanvas(unitValue, unitValue, AnchorPosition.MIDDLECENTER);
		doc.crop([0, 0, unitValue, unitValue]);
		doc.resizeImage(originalWidth, originalHeight);
	}
	
	doc.close(SaveOptions.DONOTSAVECHANGES);

})();