Indexing of images (eg /content/gallery) is rather slow

It looks like the binary data is fetched and analyzed which shouldn't be necessary.

Some numbers from a production system:

images:
08:52:09 - 13900
10:26:46 - 281000
rate: 267100/94m = 2.8k image/min

docs:
10:32:26 - 296200
10:41:06 - 439800
rate: 143600/8m = 18k docs/min

event log:
10:45:18 - 529000
11:08:18 - 1120900
rate: 591900/23m = 26k logs/min

If the binary property of the image is not fetched I would expect the images to go as fast as the event log.