[NTG-context] Issues with included images on some epub readers

[NTG-context] Issues with included images on some epub readers

[Florent Michel]

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Hi,

I'm not sure whether the following is an issue with ConTeXt or with the
epub readers I'm using; my apologies for the noise if it's not relevant to
this list!

I was experimenting creating ebooks with ConTeXt, and found it works
very well on most epub readers (except with Calibre, as was previously
reported on this list) as far as text is concerned, although I am having
issues displaying images. Images appear correctly in the exported html file
when opened with Firefox or Chromium, so I suspect the issue may either
come from difference in specs for the epub and html formats or from bugs in
the epub readers I have tried (Mupdf, Koodo, and Foliate).

Example showing the issue:

_____________________________________
% test.tex

\setupbackend
  [export=yes]

\setupinteraction
  [title={\documentvariable{title}}]

\startdocument[title=Test EPUB]

% Some text
\samplefile{tufte}

% Include a simple MetaPost image
\starttextdisplay
    \startimage
        \startMPcode
            fill fullcircle scaled 3cm withcolor darkred ;
        \stopMPcode
    \stopimage
\stoptextdisplay

% Some text again
\samplefile{tufte}

% Include an equation as SVG image
\starttextdisplay
    \startimage
        \startformula
            e = \frac{m c^2}{\sqrt{1 - v^2 / c^2}}
        \stopformula
    \stopimage
\stoptextdisplay

\stopdocument
_____________________________________

I compile it using

_____________________________________
mtxrun --script epub --images test.tex
context test.tex
mtxrun --script epub --make test.tex
_____________________________________

Render from Koodo 1.5.1 (correct): https://pasteboard.co/4bUcUdaJim9m.png
Render from Koodo's latest version (1.7.2):
https://pasteboard.co/xRfDCYx9zki4.png

All recent epub readers I have tried (Mupdf, Foliate, Okular) produce a
similar incorrect rendering.

I am not very familiar with the epub format specs so I don't have a
good feel for where the issue may come from. It seems that manually adding
    <img alt="image-1" src="../images/test-exported-1.svg">
in the .html file makes it appear with recent epub readers, though.

Is it possible to have the html output generated by ConTeXt include images
in this way (or tune the way images are included in another way which may
work better with recent epub readers)?

Cheers,
Florent

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