The Ella theme contains optional support for devices with a retina display. This support may be enabled/disabled via the theme options ( Appearance>Theme Options>Advanced Tab>Retina Support> Yes/No).
What retina support really means is that the theme will serve hi-res version of content images to decide which have a retina display. This is done automatically for all content used in the theme except for one place; The site logos.
Creating a Retina Site Logo
If retain support is enabled, a high resolution version of the site logo is required. The theme will not automatically create this, it must be done manually. See the instructions below:
Using image editing software, you will need to create a version of your logo image which is 2 times the size of your original logo. For example is your original logo is 100x50px, the retina logo will need to be 200x100px.
When creating this retina logo, there is a rule about how the retina logo has to be named. The file name must be exactly the same as the original image but with a suffix of @2x, added just before the file type.
For example, say your original image is called logo.jpg, therefore the retina image file name would be logo@2x.jpg.
Upload both the normal logo image and the 2x logo image at the same time to your WP theme insert the original logo image into the logo option in the theme options and the theme will automatically take care of the rest.