I never mentioned file size. Original post refers to MP= megapixels ![Smiley :)](https://forum.luminous-landscape.com/Smileys/default/smiley.gif)
Hi Michael,
Being curious I had a quick play my conclusion from this was that there are no issues at all with the way Adobe implements merge to pano at least on my system (Win 10 64 bit, latest ACR).
Autopano obviously works quite differently taking a lot more time to render but the main difference seems to be the production of TIFF (or other rendered file) rather than the raw/linear DNG produced by ACR or Lightroom.
FWIW, my play details From 7 NEF cylindrical projection:
ACR produced DNG = 15028 x 7981 pixels (120 MP). File size = 374 MB
Autopano TIFF = 15307 x 8017 pixels (123 MP). File size = 936 MB
Autopano TIFF (Remove Alpha Channel) 15307 x 8017 pixels (123 MP). File size = 702 MB
When opened in Photoshop:
ACR created DNG pano opens as a raw image first then reported image size = 686.3 MB
Autopano TIFF both 702.2 MB