\enabletrackers[figures.*]

\startluacode
    require("grph-wnd")
\stopluacode

\starttext

    \startcombination[2*2]
        {\externalfigure[hacker.jpeg][width=4cm]}                     {\type{no conversion}}
        {\externalfigure[hacker.jpeg][width=4cm,conversion=gray.jpg]} {\type{conversion=gray.jpg}}
        {\externalfigure[kodim03.png][width=4cm]}                     {\type{no conversion}}
        {\externalfigure[kodim03.png][width=4cm,conversion=gray.png]} {\type{conversion=gray.png}}
    \stopcombination

\stoptext
