Importing alpha with wrong values
GIMP version: 2.10.10 Operating System: Windows Package: Installer from gimp.org
Attached is a file "cralpha.bmp" that includes the letter X with mild opacity. A hex editor can be used to quickly verify that all four color components of every pixel--RGB and alpha--have the same value.
When loading the image in GIMP, the alpha channel is more opaque than it should be. At some point along the way, it was erroneously brightened. This can be verified by checking the Channels tab, which clearly depicts the corruption of the data:
Producing a layer mask by transferring the alpha channel also depicts the corruption:
The maximum opacity of any pixel in the data is 80, but after importing, GIMP is boosting it to 152. I've searched far and wide, but could find no configuration option to correct this misbehavior.
Curiously, if I use the grayscale color channels as the layer mask, convert the color channels to full white and export a new file, the resulting output has the correct opacity.