Arcmap: no more jaggies
For smooth background images in ArcMap turn on Bilinear or Cubic Convolution.
To make this the default, see “Arcmap >> Customize >> Arcmap options >> Raster >> Raster Layer >> [x] Enable Custom Rendering Defaults“.
Caveat: in maps with classified imagery like EOSD, you’ll need to alter the Layer Properties for each one back to the Nearest Neighbour as Bilinear or Cubic resampling won’t be a sensible default for all image types.
Technical explanation here.