I would say one of the top ten Aperture questions I get from users, many of whom are experienced, is asking how they select and de-select multiple images for import. I think the reason for this confusion is that it doesn’t act quite the way the Finder does in this regard. Not only can you select an image, but the check box needs to be checked for it to be imported.
Often, we shoot more than one assignment on a card and want to separate the images into their respective Projects on import. It’s a way of keeping things tidy before they are actually in the library. Otherwise, you have to go through the extra step of relocating images (in a referenced library).
Uncheck All
The first step is to “Uncheck All”I prefer to “Uncheck All” before I select which images I want to import first. Of course you do it differently if you like. You can also just uncheck the images you do not want to import.