Some sixel images are not displayed

[michaelrommel]

Hi Nicholas,

in my recent installation on Windows11/WSL2/debian trixie I encountered a strange issue. Under tmux sometimes images are not displayed, depending on their size, whereas without tmux, they are. I found this, when I was testing yazi, where, depending on the terminal width, sometimes images were not displayed. Resizing the window to a much smaller size would then display the image.

I then took a large image >4000px in width and looped over widths ranging between 1730 - 1800 using img2sixel -w $s testimage.png and saw that every now and then an image would be displayed some other times not. I attach examples of two of those files, which were obtained with two specific width settings.

I tested this under Wezterm 20250713-135109-85c587f9 and Windows Terminal Version: 1.22.12111.0 The terminal windows were sized at 149 columns x 38 lines.

Tmux was compiled from master today with utf8proc and sixel enabled. tmux config file is here: https://github.com/michaelrommel/dotfiles/blob/main/dot_config/tmux/tmux.conf

When running without tmux, the images are rendered differently: Wezterm shrinks the image, so that it fits inside the window, Windows Terminal overflows in both directions.

Inside tmux, terminals show images, that are displayed (1736) with the same smaller size:

The prerendered sixel files and the original png are here:

sixel_testimages.zip

Please tell me, which logs you would need to look into this topic, if you cannot reproduce this issue. I will try later under macos, if the issue persists there as well (Wezterm and Ghostty). If anyone else has encountered this issue, please comment if you could resolve it.

With tmux 3.5a none of the images were displayed.

Thanks,

Michael.

Edit: on macos Wezterm shows the same behaviour as under Windows/WSL. Ghostty does not support the sixel protocol. Here I can see under tmux, when I cat test_1735.six nothing gets displayed, whereas with 1736 I see the placeholder SIXEL IMAGE (92x22)+++++ displayed. This leads me to believe, that tmux itself has a problem with the 1735 image data and does not even forward it to the terminal.

Now I believe this is independent from the application img2sixel, because the same effect occurs also in yazi. I do not know (yet) if yazi is linked with the same library, but I doubt it, because it is written in Rust and the img2sixel is - I believe - much older...

[michaelrommel]

I created additional logs on Wezterm for macos, where the issue also appears:
tmux-client-24972.log
tmux-out-24974.log
tmux-server-24974.log

After the shell initialisation, the only command was cat test_1735.six with an empty response.

In the server log on line 52278 there is a discard message, which has a similar size of bytes as the image is.

1754861081.517164 input_parse_buffer: %0 dcs_handler, 516 bytes: 4@AA@@?@@A@BBBABBA?!4A?ABABAB!5ABAABAAAB!4A?@!5?@A?@???@!6?@??@#112!31?@#94???A#91@?A?@?@#178!41?@#90!13?!4A?AAA?AA?A?!7A@!10A??AA?A??A???@#211!110?@???@??@!4?@#155!215?A?@#183!115?@??@#202!6?@!5?@!9?A?@???@??@???@??@??@???@?@?@?@?@ABABABA@@AAABA@@@?@@ABABABA@B@B@!22BAA$#171!238?@??@!7?@#198!608?@#38!90?@??@!6?@#209!100?@#145!12?@???@!4?@?@!5?@?@?@??@??@?@?@!4?@?@?@??@??@?@?@??@???@??@??@!4?@??@!4?@?@!5?@??@??@??@!5?@!7?@?@???@???@??@???@$#107!1089?@!5?AB?!4A?BABABBAAABAABABBAAABABBABAAABAABAABABA?@AAABABAA?@\033\\
1754861081.517182 input_dcs_dispatch: 1048575 bytes (discard)
1754861081.517216 screen_write_collect_flush: flushed 0 items (screen_write_stop)

[michaelrommel]

With the successfully displayed image, at around the same location ther is a successful log entry:

1754861758.695768 input_parse_buffer: %0 dcs_handler, 591 bytes: @B@ABB@A@B?@@@B!5A@!4?AA#183!74?@#95A@?@?A?A?@!7?!7A@?!4A@!6AB??AA?AAA@AA!4?A???AA@??@?@??@#210!62?@#154???@!4?@!11?@!7?@?@A@?@@A@AA?@BA@AB@ABBBA?BABBB@BA!5BA!4BA!6BABBBABA!5BAABBABBBABBABABBA?ABABAAB@A@@A@A?A@A@?A@A@A@?@@AAA@AA???ABA??@A@A@AA@A??@A@AA?AA@AA??AA@@?@?AA???@!4?AA!6?AA???@!6?AA!46?A#157???A!4?A???@A???A#154!10?AA#157A#192!94?AAA??AAA???!7A?A?!4A?AA?A??A??A?!4A?!9A?!5A?AA?A$#39!933?@#118!27?@!6?@??@?A@??@BA@?A@@BA@@@A@@A@?@!4?@#91!44?A!5?A#183!5?@#112!21?A??@!7?A@A@?AAA??!4A?!7ABAAABAA@?ABAA@@?BABAABAA@AAA!5?AABA@?@#197!215?@#154!76?A#206!118?@!13?@!4?@?@??@$#207!1085?@\033\\
1754861758.719273 screen_write_collect_flush: flushed 0 items (screen_write_sixelimage)
1754861758.719297 tty_cmd_sixelimage: image is 92x22
1754861758.719303 tty_cmd_sixelimage: clamping to 0,0-92,22
1754861758.744194 tty_cmd_sixelimage: 1070427 bytes: \033P0;0q"1;1;1736;1046#0;2;96;67;8#1;2;97;63;9#2;2;97;69;16#3;2;97;63;6#4;2;97;71;2#5;2;97;71;8#6;2;97;63;3#7;2;97;60;0#8;2;96;58;5#9;2;97;56;0#10;2;97;53;0#11;2;97;50;0#12;2;96;45;5#13;2;94;47;0#14;2;94;41;0#15;2;93;39;3#16;2;94;38;8#17;2;93;36;3#18;2;91;35;3#19;2;93;33;8#20;2;91;31;3#21;2;91;28;6#22;2;91;25;6#23;2;88;28;9#24;2;88;25;6#25;2;85;24;11#26;2;88;20;6#27;2;85;19;6#28;2;82;19;6#29;2;78;16;6#30;2;75;16;6#31;2;72;16;9#32;2;72;13;6#33;2;75;13;6#34;2;69;13;6#35;2;66;13;6#36;2;66;16;9#37;2;97;47;0#38;2;85;24;6#39;2;77;19;13#40;2;82;16;6#41;2;94;35;0#42;2;89;30;13#43;2;80;22;13#44;2;69;16;6#45;2;78;13;6#46;2;71;14;9#47;2;69;13;9#48;2

tmux-client-26875.log
tmux-out-26878.log
tmux-server-26878.log

[nicm]

What if you increase input-buffer-size?

[michaelrommel]

Yes, that solves the issue where files are displayed outside tmux, but not inside. Now need to go hunt down application related errors. Thank you for the quick help!!