To reproduce:

1. Open any image that is bigger in height than in width.
2. Rotate it clockwise.
3. Make sure the window is bigger in width than in height.
4. Run scaling full command.

As you'll see, the image isn't scaled to the viewport. This is because imv uses the real size of the picture to calculate how much to scale instead of applying the rotation first. Rotating clockwise again after trying to scale makes it clearer.