I use photos from a digital camera and work with them in Photoshop/Lightroom. Today I again imported pictures from the camera into photos-app on my MacBook Pro, mid 2014, Yosemite 10.10.4/3 (I had the problem on both versions, stable and beta), and then, before I saw the export-option, copied the pictures and pasted them into Preview.
As a result, I noticed an extreme quality-loss, since the resolution always was 1024x768 by 72 pxi instead of 3072x1728 by 180 dpi (yes I know I stated different units pxi/dpi but that's the information I get from my software pix is preview, dpi is digital images, and I think there isn't much of a difference?).
I'm wondering where this comes from, also because exporting works fine, without quality-loss and I would like to know how I can see the dpi of an image with preview-app / information-option.