I didn't mention it in my previous question because it's an image format made of vectors, but would SVG provide a usable alternative for non-pixel images like illustrations?
If, how well is SVG supported by the mass of ebook readers… and is that support dependent on specific ebook formats? (Not including TXT as it's obvious you can't embed SVG into that.)
As Donald points out in his answer, (new) devices would have to support SVG 'images' as support for SVG is specified in the EPUB 3.0 standard.
For line drawings, but also for zoomable images (maps come to mind), this is a vastly superior format over any pixel based file format.
How soon that adaptation will happen will be influenced by how easy it is to adapt the various rendering engines used in the devices. Some of the features of 3.0 require more processing power, potentially reducing battery life even if not actively used.
Conversion to non-EPUB formats of EPUB 3.0 with SVG is going to be more difficult, some will not support it at all (which would require rendering in some pixel based format at some resolution), conversion to others formats (PDF) would become more complex than the current text and image conversion.
The ePub 3.0 standard specifically names SVG as one of the core media types to be supported. The 2.0 standard also names SVG as one of the supported types in the img tag documentation. So any device supporting ePub would have to be able to handle an SVG image, which is the vast majority.
The 2014.1 version of the "Amazon Kindle Publishing Guidelines" indicates support for many SVG elements -- including -- see page 26.
I'm not entirely sure whether the svg can include embedded bitmaps though.
Also, http://epubtest.org/compare/ has some entries for device support by svg feature. Significantly I note that Kindle data has not been filled in, and ibooks isn't even listed.
This article from 2013 says:
for some reason, SVG image support in modern products is still a kind of an afterthought, and it shows. The EPUB standards authors were nice enough to include support for these files in the EPUB standards, which is great in principle, yet they included content negotiation mechanisms so that SVG support is still technically optional. This in turn means that the content authors are forced to include alternatives for their SVG content in case the ebook reader author couldn't be arsed to support this format.
But newer versions of ADE seem to support SVG even on the spine.
Then again, how many people buy a new eBook reader every year (or make updates). So we will have to deal with older devices for quite some time...
