@afre
I do not understand what you mean by “the alpha being grey scale”. The alpha-channel is the same as the other channels, it is 16bit “greyscale”.
I have repeated your measurements for the version which was load and exported as TIF in GIMP. This clearly also shows the problem:
| No | mean | std | min | max | median |
|---|---|---|---|---|---|
| 1 | 38505 | 8831 | 2069 | 65535 | 37629 |
| 2 | 13175 | 4621 | 752 | 29167 | 11767 |
| 3 | 5691 | 1373 | 304 | 10904 | 5760 |
| 4 | 50701 | 1893 | 6224 | 56832 | 50960 |
| 5 | 38096 | 8081 | 2069 | 56160 | 37628 |
| 6 | 13175 | 4621 | 752 | 29167 | 11767 |
| 7 | 5691 | 1373 | 304 | 10904 | 5760 |
| 8 | 50701 | 1893 | 6224 | 56832 | 50960 |
Measurements 5 … 8 refer to the output from GIMP. The R-channel changed but shouldn’t, the others are the same as in the input image, which is correct.
I just installed the new GIMP version to see, if the problem remains. But there is an error message right at start, so I have to wait until this is solved. Re-installation of GIMP does not solve this issue.
Hermann-Josef