To support Retina or HiDPI displays, the icons provided by the XMLNodeRendererCustomizer should be backed up by a copy of larger size using the proper Retina/HiDPI naming convention.
For example, for the <title> element, if the
XMLNodeRendererCustomizer returns the path
${framework}/images/myImg.png, then to support Retina images with a
scaling factor of 2, an extra file (myImg@2x.png)should be added to the
same images directory (${framework}/images/myImg@2x.png). If the higher
resolution icon (the @2x file) does not exist, the normal icon is scaled and
used instead.
For more information about using Retina/HiDPI images, refer to the Using Retina/HiDPI Images in Author Mode section.