ImageMagick convert from TikZ figure produces weird result

Question

Problem

I am getting two different results when using TikZ and standalone to convert to png. The same happens when I directly use ImageMagick 6.8 convert from.pdf to.png as well.

Why does this happen...?

Expected result

The output should look like

Actual result

The result of running either lualatex or convert tikzmwe.pdf tikzmwe.png is the same and results in the following png.

convert also give me this message:

convert: profile 'icc': 'RGB ': RGB color space not permitted on grayscale PNG 'tikzmwe.png' @ warning/png.c/MagickPNGWarningHandler/1748.

Minimum working example

\documentclass[varwidth=true, border=0pt, convert={outext=.png}]{standalone}
\usepackage{tikz}
\usepackage{xcolor}
\newcommand{\sharedkey}{%
    \raisebox{-.5 ex}{\tikz{%
    \draw[fill=blue, draw=white] (0ex,0) arc(90:270:1ex) -- cycle;
    \draw[fill=red, draw=white] (0ex,0) arc(90:-90:1ex) -- cycle; }}}
\begin{document}
\(x = \sharedkey\)
\end{document}

Compile with lualatex -shell-escape tikzmwe.tex.

Thanks!

Answer 1

This looks like an ImageMagick bug to me. I checked on two versions and got different results:

Cannot reproduce:

• Version: ImageMagick 6.8.9-9 Q16 x86_64 2019-11-12

Can reproduce:

• Version: ImageMagick 6.9.11-24 Q16 x86_64 20200718

  (not seeing the warning, though)

The halving of the circle is excess white from the draw=white: when using another stroke color, the lower circle half is entirely filled with that color.

I wasn't able to check on the current ImageMagick 7. Filing a bug is only an option if the bug can be reproduced on the current stable version.