[speeddemon]

I figured something like that was the case, thank you for the explanation. Still that seems like a bad hack that terminals are not going to implement because it goes off-spec. It seems as if iTerm or kitty protocols (or anything else designed for a real screen and not a printer) would be a much better choice for a terminal trying to choose.

[noergl]

Well it is not that bad, imho all newer terminal implementations, that dont try to strictly emulate a VT340, do sixel this way. libsixel even propagates this as "highcolor". But again, sixel is still limited to ~1M colors in RGB and ~3M colors in HSL, even with that implementation trick.

The sixel format has much bigger issues beside its reduced color resolution - no alpha channel, need for really expensive quantization and printer head movements serialization, with bad cache locality due to its 6-pixel offset in y direction. Its compression is lousy. All that said, encoding/decoding sixels is a mainly CPU-bound resource hungry task with high bandwidth needs - all for worse quality compared to modern formats. With modern hardware, where beefy GPUs exist, it is really a shame to insist on using this format (which was effectively dead for >20ys).

On terminal side there are more issues about sixels and how they relate to cursor advance and the terminal grid, but going into these details will only bore ppl in a rant thread.