One of the new subtleties of Photos is how it treats exporting your pictures. There are two ways to get your images out of the Photos app, one that will give you a smaller file, and one that will preserve the higher resolution, original photo.
Here’s how to make sure you’re exporting your photos at the quality you want.
You can drag and drop your pictures from the Photos app to the Desktop, or you can use the Export menu (in the File menu).
If you use the menu, you’ll see two options when you select Export: “Export X Photos” and Export Unmodified Original For X Photos,” where X is the number of images you’ve selected.
The first option will net you a JPG file, whether or not your original photo is of the same format. It will also be more compressed, as the file size will generally be smaller than the original image. For example, I exported a screenshot I’d taken with my iPhone with this basic Export menu item, and the the file size shrunk from a 3.8 MB PNG to a 452 KB JPG. This is great if you need a smaller file size, but the image quality will suffer.
To preserve the original file, format, and even date created timestamp, use the second option (Export Unmodified Original) and you’ll get an exact duplicate of the photo.
You can do the same with drag and drop. To export a JPG at a lower quality/higher compression, simply drag and drop the image from Photos to your Desktop. If you want to export an exact duplicate of the original file, however, hold the Option key down when dragging – you’ll get the higher quality original photo instead.