A script to export your pictures for the web sized non-retina and retina. Open all images in Photoshop and run the script:
File / Scripts / ExportDocumentForWeb_FullAuto
It will create a folder "ExportForWeb" and place all images there. You can close your original pictures without saving. This script will save a PNG in 100%.
##Set desired screen sizes: Open the file and set your sizes in arrayOfSizes. Leave the first value as it is for it's original size.
var arrayOfSizes = [app.activeDocument.width.value, 1200, 992, 768, 360, 320];
Program / FilesAdobeAdobe / Photoshop CC 2015 / Presets / Scripts
Applications / Adobe Photoshop CC / Presets / Scripts
##Notes:
Based on Murdoch Carpenter's script. http://murdochcarpenter.com/blog/. Tested in Photoshop CC (2015.5.1) V2.0
##More information: Smashing Magazine Article of Mr Carpenter