Why does Preview lower image-quality 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.

Thank you,

Gabriel/Gabkano
The Preview does not lower the image quality, but will fit it in the given parameters.

If you use Preview to open a original image: Example:

5.5 MB file size with Dimensions of 3648 × 2736 pixels

Now open the Preview Tools - Adjust Size to see the current settings.

The default resolution is set to 72 which is standard for web applications.

In that window you can set it to the original size/resolution.



Now if you are using a copy/paste to move the image to Preview, the resulting quality will depend on the copy/paste settings. That can be found in the application it self.