Viewer for HEIF/HEIC images in El Capitan or Sierra Is there any "native way" to view the new HEIF/HEIC format (or the viewer-application) in El Capitan or Sierra without upgrade of MacOS itself? It is not yet possible to upgrade yet to HighSierra for me, but I'd like to natively view images from iPhone 8 and up generation, avoiding conversions to JPG.

There been questions asked about convertors of .heic to .jpg, but I don't think it's reasonable to convert images (via the means of online convertors, specialized apps, Dropbox, etc.). Soon or later .heic support will become normal, and all the online services and applications will finish the transition, so obviously there will be no need to convert to JPG. 

The question: Is there any way to install some kind of plugin or extension to MacOS to support HEIF/HEIC within the Preview App, or it may be there are good applications alike XnView or analogues, which support it out of the box?
The current version of Graphic Converter (from https://www.lemkesoft.de, free trial available) supports HEIC format.  I did not try it in Sierra or El Capitan, but the description says: MacOS 10.9 or later.