This issue involves transferring changesets from the following HSC issues:
- HSC-145 Investigate approximating rather than interpolating backgrounds
- HSC-1047 Background object cannot be loaded with butler
- HSC-1213 Set background 'approximate' control settings when background control is created.
- HSC-1221 tests failing in ip_diffim
- HSC-1217 Verify backgroundList IO works properly when Approximate is enabled in background control - HSC JIRA
The Approximate (Chebyshev) approach greatly improves the background subtraction around bright objects compared with the interpolation scheme currently in use (which over-subtracts near bright objects).