PDHFIC is an image conversion program for Amiga, capable of converting colour pictures into Spectrum .SCR, .TAP, .header/.bytes, +3DOS and ZX82 formats.

PDHFIC has a small GUI, and full Workbench support. It can load pictures using the OS3.x Datatypes system (it can also load some PPMs and pictures stored in the clipboard), and will scale or truncate pictures to the correct size. It will map colours to the Spectrum palette, dithering them if requested. It will output both with and without colour attributes, supporting BRIGHT and FLASH. It also has an ARexx port.

Take a look at the example pictures on this site to see the sort of results to expect. Unsatisfactory Software are currently the only developers of Amiga to Spectrum image convertors.