Sixel encoder/decoder

[Nutzzz]

Especially now that Windows will be supporting Sixel in ConPty/Windows Terminal (Note Windows Terminal Canary supports it today, and it should be in mainline soon, probably in the next couple of weeks), perhaps an encoder/decoder could be added to ImageSharp? I'd really love it here, otherwise I'd have to either do a PInvoke of libsixel or switch to Magick.NET. Thanks!

[JimBobSquarePants]

That’s a pretty obscure format so we wouldn’t dedicate any time to supporting it any time soon. Perhaps via community contribution though.

[Nutzzz]

Sure, but that was my point; its obscurity has been partly due to the relative lack of support, which is changing.

I made a quick C# proof of concept that sort of works, but it currently only uses one color per 6-pixel high block (so it looks a bit like ANSI art). I'll try to continue developing it.

[JimBobSquarePants]

Ah that’s excellent! Are you using libsixel as reference?

https://github.com/saitoha/libsixel

The code there looks fairly readable.

[Nutzzz]

I used this "experimental" library in C# that turned out to be completely broken. My proof of concept was, for fun, attempting to fix it based only on the sixel Wikipedia article. As far as using libsixel (or chafa, perhaps) as reference... to the extent I'm good at any language, standard C ain't it.

[trackd]

Hey!
Me and ShaunLawrie made a Sixel PowerShell Module using Sixlabors lib.
trackd/Sixel
It works quite well and supports 256 colors, transparent etc.
(Max in WT)

Also Shaun has a PR open in SpectreConsole to add the sixel code there as well :)

So should be fairly accessible soon.

[JimBobSquarePants]

Very interesting! It looks like a lot of the code could be borrowed to write an instance of IImageEncoder. I couldn't find decoding code though? How does that work.

[Nutzzz]

Also Shaun has a PR open in SpectreConsole to add the sixel code there as well :)

Note that Sixel support was recently added to the V2 prerelease of the other major C# TUI framework, Terminal.Gui.

[trackd]

Very interesting! It looks like a lot of the code could be borrowed to write an instance of IImageEncoder. I couldn't find decoding code though? How does that work.

correct, i never made a decoder. I didn't really have a need for one.

SixPix.NET does have a decoder, but i havn't tried it.

Also Shaun has a PR open in SpectreConsole to add the sixel code there as well :)

Note that Sixel support was recently added to the V2 prerelease of the other major C# TUI framework, Terminal.Gui.

Yea i saw that a few days ago, looks interesting. havn't had a chance to test it.

[JimBobSquarePants]

Looking at SixPix.NET it looks like decoding is trivial however I'm struggling to find any specifications for the format and specifically:

• How alpha support works.
• Can Sixel support multi-frame images?

I'm absolutely happy to work with someone to add official encoders and decoders to the library for V4.

[trackd]

Looking at SixPix.NET it looks like decoding is trivial however I'm struggling to find any specifications for the format and specifically:

* How alpha support works.

It needs to be enabled in the start parameters 1 ("{ESC}P0;1q") to enable transparent mode.
and then you reference color 0 => "#0;2;0;0;0"; with sixel ?

so in my code it's this line that adds the transparent sixel.
Append(color != 0 ? e : Constants.SIXELEMPTY)

graphicrenditions.md this repo has alot of information and the original docs.

wt sixel parser is pretty readable and with alot of comments.

* Can Sixel support multi-frame images?

sort of, but it's pretty limited.. WT supports 6 pages.
microsoft/terminal#17421 (comment)
the first example there is one of the few i've ever seen.
Most animations using sixel use some sort of script/code to orchestrate the timing & drawing