Is it possible to simply use Save for Web with resizing to produce images without black edges?
My current Save for Web setting
Top right: Save for Web (black edges)
Middle right: bicubic resize then save
Bottom right: add a layer mask from transparency, resize then save (black edges)
Save for Web
Resize then save
Add a layer mask from transparency, resize then save
In Photoshop CC 2015, the new Export As solves the problem. It does not produce black edges when resizing but the Save for Web (Legacy) still does.