  Magnetic spin resonance is a key non-invasive sensing and imaging technique
across the life-, material- and fundamental sciences with further medical and
commercial applications. Recent advances using paramagnetic color centers
enable magnetic resonance down on the nanoscale, and sensitivity to single
molecules is in sight. Ensemble sensing and wide field imaging improve
sensitivity and acquisition speed, but may suffer from inhomogeneous spin
control fields, produced by e.g. microstructures in integrated devices, and
limited spatial resolution. Here we demonstrate multiplexed nuclear magnetic
resonance imaging using diamond nitrogen-vacancy centers in such adverse
conditions. We image thin films of calcium fluoride down to $1.2\,\mathrm{nm}$
in thickness with a spatial resolution of $250\,\mathrm{nm}$. This corresponds
to a net moment of about 140 nuclear spins within the sensing radius of a given
NV in the ensemble.
