Show only captions

Is there a filter I can add to functions.php so that photos in a wordpress gallery will show the caption and nothing but the caption? By caption I mean post_excerpt.

I know you can show the caption by selecting “Allow title from thumbnail alt tag”, but if no caption has been set the image title (post_title) is used, resulting in numbered .jpegs being displayed as the title

Given the number of photos uploaded to the site I don’t want to edit the title of each one, just add a caption in certain cases and have that displayed.