...another version of SSTV I hadn't heard of until a day or two ago...N-SSTV (Narrow SSTV)...
It appears to be identical in all respects to conventional SSTV, whatever mode is in use, except that the usual 1200-2300Hz sub-carrier is 'squashed' down into 1900-2300Hz. That's an advantage on the noisy and crowded HF Amatuer bands, less so with what I'm generally interested in. But it's an easy modification/addition to existing systems.
Example off-air screen-shots seem much the same as the usual standard, no better nor no worse, maybe more so in marginal conditions. Start here if curious or interested...
https://narrowsstv.wordpress.com/
Steve A.
It seems that these N-SSTV modes have been around quite some time - years! - not come across them until two days ago!