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.