I read a thread that was posted a while back, about 2005, about rendering with a transparent background. He suggested pressing the RGBA button in the Render window, and that that would render a transparent background, but I am still getting a blue background. Why? Is there something additional that needs to be done? My issue is that I have an object with a transparent material that I need to be able to separate from the background in Photoshop to place on another image.
That blue background is the sky and it is totally transparent but is what is known as a PreMultiplied alpha channel. You’ll get halos around objects with the Sky or Premul options. Use the "Key option on the render tab instead when exporting for Photoshop. It will look scary when you see it in Blender but Photoshop knows exactly what to do with these “Keyed” or “Straight” alpha channels.