I would like to inspect images in Windows Explorer on W7 in greater detail on a big screen. Thumbnails are by default limited to ~ 256x256 px. Is there a way to increase the upper bound or some 3rd party solution? Intensive googling didn't help.
The largest thumbnails supported in Windows Explorer are 256x256 pixels. Beyond that you need to use a 3rd party program like ACDSee. In ACDSee, the size of the thumbnails in the thumbnail view is limited to 320 pixel. For larger thumbnails you can include this into your registry:
This gives the choice to move the thumbnail size slider from 25 up to 1024 pixels.