A retina logo image is the same as the normal logo image, though twice the size. For example, if one’s regular logo image is 100×100 pixels in size, the retina logo image would need to be 200×200 pixels in size.
Additionally, how you name the retina image is very important. It must be named the exact same as the regular logo image, though with @2x added onto the end of the name.
So, if the regular logo image was named “logo.png”, the retina logo image would need to be named “logo@2x. png”.