Ok, I've found a solution.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\enabletrackers[graphics.conversion]

\startluacode
local function convert(oldname, newname)
    os.execute(string.format(
        'gm convert "%s" "%s"', oldname, newname)
    )
end

-- Set the PDF, JPEG and default TIFF converters to the above function.
figures.converters.tif.pdf = convert
figures.converters.tif.jpg = convert
figures.converters.tif.default = convert
\stopluacode

\setfigureconversion[tif][jpg] % has no effect

\starttext

\externalfigure[test.tif][conversion=jpg]

\stoptext
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Would it make sense to add
tifconverter.pdf = converter
to grph-con.lua (line 293) ?

Why is it that \setfigureconversion has no effect? Without conversion=jpg on \externalfigure, ConTeXt insists on converting to PDF. (I couldn't find the command in the sources, but I'm not getting a undef'ed cs error either, so it must be defined somewhere...)

I've also found out I can use a custom command that calls \externalfigure with the right settings depending on the filetype:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\enabletrackers[graphics.conversion]

\startluacode
local function convert(oldname, newname)
    os.execute(string.format(
        'gm convert "%s" "%s"', oldname, newname)
    )
end

-- Set the PDF and default TIFF converters to the above function.
figures.converters.tif.pdf = convert
figures.converters.tif.jpg = convert
figures.converters.tif.default = convert
\stopluacode

\setfigureconversion[tif][jpg] % has no effect

\defineexternalfigure[tif][conversion=jpg]

\starttexdefinition includegraphics #1
  \splitfilename{#1}

  \processaction[\splitofftype][
    tif=>{\externalfigure[#1][tif]},
    default=>{\externalfigure[#1]},
    unknown=>{\externalfigure[#1]}
  ]
\stoptexdefinition

\starttext

\includegraphics{test.tif} % will be converted to jpg

\externalfigure[test.tif] % will be converted to pdf

\stoptext
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

But I think it would be nicer to stick to the default \externalfigure.

Best,
Denis

Von: denis.maier@unibe.ch <denis.maier@unibe.ch>
Gesendet: Dienstag, 12. September 2023 17:09
An: ntg-context@ntg.nl
Betreff: [NTG-context] Re: tiffs: autoconversion via graphicsmagick produces invalid pdfs

Sorry, that was too quick...

Hi,

currently, ConTeXt can't use tiffs directly, but it uses Graphicsmagick to convert tiffs to pdf on the fly. However, as it seems, graphicsmagick is producing invalid pdfs.

For every included tiff I have something like this in the log:
luatex warning  > pdfe: invalid 11 0 R object at offset 573751
luatex warning  > pdfe: invalid 11 0 R object at offset 629127

The offsets are different, but it's always this <invalid 11 0 R object>.

This bug has been known for quite some time, but it apparently hasn't been fixed yet: https://sourceforge.net/p/graphicsmagick/bugs/513/

Converting the tiffs to jpeg circumvents the problem. Would it be an option to convert tiffs to jpegs instead of to pdf? (Is that already possible?)

Best,
Denis



Von: denis.maier@unibe.ch<mailto:denis.maier@unibe.ch> <denis.maier@unibe.ch<mailto:denis.maier@unibe.ch>>
Gesendet: Dienstag, 12. September 2023 17:03
An: ntg-context@ntg.nl<mailto:ntg-context@ntg.nl>
Betreff: [NTG-context] tiffs: autoconversion via graphicsmagick produces invalid pdfs

Hi,

currently, ConTeXt can't use tiffs directly, but it uses