You need to save as PNG – but not any old PNG will work.

I have consistent success using Paint.NET, deleting the “background” so it is empty (checkerboard), then saving as a PNG.  But here’s the main lesson – make sure you tick 32-bit.  No other option seems to work, only 32-bit PNGs seem to respect transparency in Revit.

You can even use Bring to Front, Send to Back etc to overlap these images.  Quite useful for Entourage in coloured Plans and Elevations…

The Revit Kid demonstrated today that PNG files exported from a Revit render have no background.

In the spirit of one-up-man-ship, I recommend that you use TIF if you want to keep the background, but quickly separate it from the model elements.  When you export as TIF, you get a bonus Alpha channel that you can use to create a selection area and move the background to a new layer.

In simple terms:

  1. Export Revit render as TIF
  2. Open in Photoshop
  3. Isolate the Alpha channel
  4. Use Magic Wand to pick everything that is ‘white’
  5. Turn the color channels back on
  6. Invert the Selection
  7. Convert the background to a true layer
  8. Edit – Cut
  9. New Layer
  10. Edit – Paste
  11. Done!

Now you can manipulate the model elements and the background separately.

Here is a video:

 
Of course, you can also do this easily by:

  1. Doing two separate renders, 
  2. one of them with Model Elements turned off (which will just show the background) – Export this to any format except PNG
  3. and one of them with Model Elements on (export this to PNG)
  4. Copy and paste these two images to separate layers in Photoshop

 The TIF method is probably quicker and easier in most instances.

Here is a link to the aforementioned PNG post:
The Revit Kid.com!: Revit Tip – Export Rendered Images Without a Background