Retina images are hi-def versions of all your graphics and images for use on devices that have retina screens or a very high resolution. This is so your website maintains a high-quality appearance on high DPI screens. Normal images are exported at 96DPI, whereas retina images are exported at 192DPI.
How do I enable this option?
By default, this option is enabled. You can find it however in the Utilities > Web Properties > Website tab.
How will I know that Xara is exporting the hi-res images?
You may notice in the [filename]_htm_files folder that gets exported with your website there are numerous images with @2 at the end. These are retina versions of your images. If you have more than one variant in your document, Xara will export retina images for them as well, so you would see @3 and so on for as many variants as you have.
Will this increase the load time of my pages?
Xara uses a script to detect the screen type first, and then decides whether to load the hi-def images. This means normal users on desktops and some tablets / mobile devices who can't take advantage* of the hi-def images won't suffer from longer load times, however if the device is retina capable then you may notice the pages take slightly longer to load.
*Users would not notice a difference in quality if the desktop version loaded the retina versions of your images, excluding those with retina displays in which it will load the retina version.
Memory usage on export and optimization.
More memory is required to render the higher resolution images, so users with larger websites (including those with variants) running either the 32 bit version of Xara or with limited memory may get an out of memory error on export. Should this happen and wish to keep the retina images, you will need to split your website between multiple files. Otherwise, simply switch off the retina option and it should then export.
If you try to optimize all images when the retina option is enabled, you'll see it will optimize all images to 192dpi, but will still export the 96dpi version on export.
Exporting a Retina version of your Image.
From version 11 (excluding Web Designer standard) you can now export a Retina version of your image along with a standard version. To do this, simply select the option 'Also export Retina (192dpi) bitmap' when exporting as a jpg under the tab 'Bitmap'.