I have tried it with the following results:
Opening an jpg-image with a size of 3150 x 2362 pixels @ 72 dpi.
Resize Document to 3150 x 2362 pixels @ 300 dpi.
Exporting this resized document as jpg-image.
Exporting same document as .afphoto file
Saved as .afphoto-file, the changed resolution (same pixel number but 300dpi now) was saved correctly
Exported as .jpg-file with another name, the changed resolution was not maintained. The image also has 3150 x 2362 pixels @ 72 dpi.
I than performed the unsharp mask filter. Interresting: The effect of the filter was correctly saved as .afphoto file as well as .jpg file.
It seems, that the resolution settings was not correctly exported in jpg-files.
One more strange thing: The .afphoto file of the image with performed unsharp mask has now 23 MByte, where the jpg-file with performed unsharp mask has 929 KB. Seems, that afphoto-files needs a very big amount of memory space (why?).
Best regards
Martin
P.S.: I have attached the original jpg-image, the (not)resized jpg-image and the resized afphoto-file.
Image - changed version 1 - 3150x2362px 300dpi.afphoto