Markdown latex formulas render as image

[relma2]

I am using a TUI email client which writes emails in plaintext, and I am using Pandoc to convert them to HTML assuming that the plaintext has Markdown-style syntax. I am enclosing a simple $\LaTeX$ formula in my markdown with dollar signs, and instructing Pandoc to use MathJax/MathML in its HTML output. The problem is, this works fine when viewing the HTML in a browser, but not within an email client.

What I want is for the $\LaTeX$ to be converted to an inline image containing the formula and embed into the HTML output, like this:

Input markdown:

This is the quadratic formula:
$$
x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
$$

Output HTML:

<p>This is the quadratic formula:<br />
<!-- Image showing rendered LaTeX output -->
</p>

Is there a way to make Pandoc call some kind of script to make it do this?

[N1N74]

Woah, great coincidence, I also had the exact same usecase and have been trying to work with a lua filter which uses mathjax-node to convert equations into svg. Problem I'm stuck at is [WARNING] Could not convert TeX math which will not mark the equations as equations and the filter won't act on it. I got it working on simple equations like a=b but falls on it's face if it's like \frac{1}{2} which is just really annoying. See #7771.
Dunno what to do here, tried adding filter at every "at" stage, nothing seemed to work. Quarto converting to md doesn't throw this error and works but there's some quirks like getting equations in headings to render.

PS Let us know any alternatives if you ever find something!

[N1N74]

If you don't mind error with fonts or equations looking kinda off, prerendered equations works with such a thing. Here's code I've tested it with. Feel free to use other filters that also try to prerender equations.

[jgm]

Have you seen this? https://github.com/pandoc/lua-filters/tree/master/math2svg

[relma2]

That allows for embedding an svg equation into an html, but unfortunately embed svg's don't show up in GUI email clients

[jgm]

It could be modified fairly easily to instead include an Image with a base64-encoded svg data: URL.

[relma2]

@N1N74 So I found a way to embed images into the output HTML using the --webtex option. Webtex is a proprietary backendpoint on the internet that pandoc can call to render a $\LaTeX$ equation, and the resulting pipeline can be called with

pandoc -f markdown+tex_math_dollars -t html5 --webtex --embed-resource --standalone

assuming the input markdown is coming from stdin.

Unfortunately there is one limitation with this method. Webtex only does dark text on a transparent background, so if the email client is using a dark theme then it's really hard to see. @jgm how do we make Webtex output a white background; or allow inverting of the image if a dark theme is detected?

[relma2]

Also the inline images have the style vertical-align: middle; which I don't want. How do I get rid of that?

[N1N74]

@relma2 try --mathml instead of webtex, I checked that this worked on roundcube, now it feels stupid to have tried coming up with a filter lol. I checked darkmode and lightmode in roundcube and it changes color as expected. Also tested works on firefox, chrome, thunderbird but there maybe browsers or email clients that don't support mathml that may have issues. Also some minor quirks like \mathbb{R} looks ugly in firefox compared to chrome, I guess each implementation of this differs but I think it gets the job done.