Rendering PNG with Alpha

Do the png’s I save out of Blender come with an alpha channel option?

The idea is I want to be able to render out architectural interiors where I have an image being used for outside the window, but it would be better to be able to have that image plane not render and leave the window areas blank and put the BG back in post (option for changing it, color correction and so on). And if I do render that out, will any reflections on the window glass survive?

If PNG is the wrong option here what are others using to do this sort of process?


Here’s a scene that has all the basic elements. How do I make the Green Emissive Plane outside the window not show up in a render but still have a lighting effect on all the other objects?

window test.blend (548 KB)

You can’t use refractive shaders on the window (= Glass or Refraction shader), as those will always render opaque to capture the refraction. And BTW, why would you? The refractive effect of window glass is negligible anyway. Use a Transparent/Glossy mix instead:

https://dl.dropboxusercontent.com/u/27650383/15-08-2017%2012-05-01.png

In that render I cranked up the emission of the green plane to better show the effect. Also: Make sure that only “Camera” and “Shadow” are disabled for the green plane’s visibility.

https://dl.dropboxusercontent.com/u/27650383/15-08-2017%2012-07-39.png

Ah thanks, that actually makes sense. How do I set up properties so that the background (non geometry) doesn’t show, I don’t get a window hole in my alpha channel in a EXR for example.

Okay, I found the answer to this as well. Under Render properties editor scroll down to ‘Film’ and check the box ‘Transparent’.

That’s a weird place to put that.