The Official Feed Viewer Blog
Consuming as less network bandwidth as possible was always a priority. Feed Viewer client is downloading a lot of images. They are preprocessed by Feed Viewer online service. Tile images are resized and encoded into JPEG XR format. This format is very good but it is limited to Windows devices only. There is a lack of image libraries that would be supporting this format. Windows 10 is inconsistent because Live Tiles still missing JPEG XR support. Feed Viewer will be available on another platform soon and adoption of portable image format is necessary.
JPEG is still much more efficient over PNG with color quantization. There is an option of HEIF in future. Everything is about finding the center of gravity of the triangle with three vertexes – quality, compression ratio and cost of implementation. The backend was designed to serve different file formats to different devices, but latest and currently planned features are almost impossible to implement with this design decision.
Feed Viewer was always limited by hardware performance, operating system restrictions and backend running costs. Portability is another boundary that must be considered. For choosing a 25 years old technology in IT must be a serious reason. When you look around, everybody would like to use a better format, but there is just not a better alternative yet.