\useMPlibrary[dum]

\starttext

\startcombination [nx=3,ny=1]
    {\externalfigure[dummy][width=2cm]} {2cm}
    {\externalfigure[dummy][width=3cm]} {3cm}
    {\externalfigure[dummy][width=4cm]} {4cm}
\stopcombination

\stoptext
