XnView lightens an image that I don't want lightened.

[DemonDuck]

A Fuji RAF file -- I convert it to TIFF and rotate 90 degrees counter clockwise. The image then becomes much much lighter.

I don't want it to become much, much lighter. It's part of a panoramic sequence and if it becomes lighter, it no longer fits into the sequence.

How do I tell XnView that it's doing something that it is not supposed to do?

[xnview]

A Fuji RAF file -- I convert it to TIFF and rotate 90 degrees counter clockwise. The image then becomes much much lighter.

I don't want it to become much, much lighter. It's part of a panoramic sequence and if it becomes lighter, it no longer fits into the sequence.

How do I tell XnView that it's doing something that it is not supposed to do?

Have you changed the view gamma (in Tools > Options > View > Misc > Use gamma correction)? If not, send me your RAF file.