EYE_OF_HORUS  Users of this app might compare it with

QuickImageCM, a very useful 2D viewer. Free and available on MacUpdate.

As a CM it operates in background, right mouse click brings popup screen to launch viewer on selected image files.

For example, it handles:

1. multiple pdf files, showing 1st page of each. Highlight all or only the files you want to review.

2. can save image files in different formats. I use jpeg to psd frequently

3. has basic image handling and image effects, keyboard shortcuts (eg trash)  
(Version 1.5.2)