Appion

First, while a user is viewing all non-hidden images, there is no way to tell if an image is an exemplar or not. which is why there is no un-exemplar button in this mode.

This bug does make a good logic point that the "exemplar" and "hide" button are shown all the time while what they do vary. In some cases, they are not supposed to work at all.

r15054 does what I think is easier to understand. Tests to be made to check these behaviors.
r15055 creates keyboard short cuts for undo exemplar and unhide.

1. When preset is selected to be atlas, it can't be hide or made into exemplar. These function are for single images.

2. When preset is set to "exemplar", a button called "undo exemplar" shows up to remove the selected image. The "exemplar" button is no longer shown because it does nothing in this case.

3. When preset is set to "hidden", a button called "unhide" shows up to remove the hidden image from hide list.

works for me.

Hidden images can be unhid:

exemplar images can be unexemplarized:

atlases don't have any options associated with them.