Photoshop

In AE, composition > Save frame as.. > File

it will add an item to the Render Queue, set to export a still image file. Choose PSD.

(You can choose from a number of still image formats, including PSD, PNG, TIFF, etc. Note that in these cases the alpha channel will be available to Photoshop, but not applied directly as transparency.)

Then you just need to select the alpha channel in the Channels panel in Photoshop, and create a layer mask from the alpha.

To do so.. Ctrl-Click on the Alpha Channel, and then make sure the layer you want the mask on is highlighted, and go to “Layer-Layer Mask” and then you’ll have options for “hide selection” and “reveal selection.”

Of you can click the “New Layer Mask” icon in the layers palette instead of using the “Layer-Layer Mask” menu item.

(Also, it’s very important that in the Render Queue you set the Alpha Channel type as Straght/Unmatted, since that’s what PS handles better. But may cause graphic glitches too, so try both.)

Select–>Color Range, then select the white. Delete the white. Layer–>Matting–>Remove White Matte to clean up edges. That’s the down and dirty way.

For best results, bezier pen the logo out. Cut into the edges a little and you shouldn’t have white fringes around them.

*OR*

1. Use the Magic Wand tool to select all the white areas. (set the tolerance level higher or lower to get all of the white, but nothing of the parts you want to keep).

2. Use Select/Invert Selection.

3. CTRL+C to copy the selection.

4. Open a new image with a transparent background.

5. CTRL+V to paste the data into the new image.