P: Add support for Google Pixel depth maps

[JeanG_FR]

As discussed in this thread, depth maps from Google Pixel phones (at least 4a models) are not supported, and seem to increase the size of the catalog in an unexpected manner (over 1MB per picture). It would be nice to add support for Google Pixel depth maps and store them in a more efficient way.

[johnrellis]

From the other thread:

With those sample pics, I observed similar increases in catalog size: 1.51 MB / photo was added to the .lrcat file, a 27% overhead in total disk space used by .jpgs. For comparison, importing regular JPEGs adds about 5 - 8K per photo to the catalog.

Poking around, the increase comes from the XMP metadata added by the camera that LR stores in the catalog in its entirety.  Almost all the bytes of that metadata are consumed by two encoded JPEGs:

- a 2688 x 2016 full-color reduced-resolution preview of the full image (about 1.3 MB)

- a  JPEG 2688 x 2016 monochrome JPEG that is the actual depth map (about 0.23 MB, see below).

I don't know why the full-color preview is included in that Google metadata.  I skimmed Google's developer docs and other random posts about Pixel depth data and couldn't learn anything.  The actual depth map is relatively small, about 0.23 MB. 

Maybe if Adobe decides to support Google depth maps, LR would then store the Pixel metadata more efficiently.