Graphics

Terminals display images through three live protocols and two historical ones. None is a standard; each was defined by one vendor and adopted by others to varying degrees.

The protocols

Protocol	Status	Transport	Pixel formats	Placement model	Page
Sixel	DEC	DCS q … ST	Indexed palette, encoded six pixels per byte	Painted at the cursor, scrolls with text	Sixel
iTerm2 inline images	Extension	OSC 1337 ; File=… BEL	Any file format the emulator decodes	Occupies a cell rectangle at the cursor	iTerm2
Kitty graphics	Extension	APC G … ST	RGB, RGBA, PNG; zlib; file and shm	Stored images with independent placements, z-order, and Unicode placeholders	Kitty
ReGIS	DEC	DCS p … ST	Vector commands	Separate graphics plane	Legacy
Tektronix 4014	xterm	Mode switch	Vector	Separate window	Legacy

Lifecycle model

The questions an application must ask of every protocol:

• Does the image scroll? Sixel and iTerm2 images are attached to the rows they were drawn on and scroll into scrollback with them. Kitty placements are attached to cells by default and can be pinned with virtual placements.
• What happens on the alternate screen? Images drawn on the alternate screen are discarded when it is left, in all three protocols.
• Can the application delete it? Only the Kitty protocol has a delete command. Sixel and iTerm2 images are removed by erasing the cells under them (ED, EL) or scrolling them away; emulators differ on whether partial erasure clips the image.
• What happens on resize? Cell-anchored images keep their cell rectangle and are rescaled or clipped; pixel-anchored images may not move. Behavior is emulator-specific in every protocol.
• Where is the cursor afterward? Sixel uses mode ?8452; iTerm2 places the cursor after the image unless doNotMoveCursor=1; Kitty places it after the image unless C=1.

Detection

• Sixel: send CSI c and look for parameter 4 in the DA1 reply.
• Kitty: send a query APC G i=31,s=1,v=1,a=q,t=d,f=24 ; AAAA ST and wait for APC G i=31;OK ST.
• iTerm2: TERM_PROGRAM=iTerm.app or TERM_PROGRAM=WezTerm; there is no in-band query.

Always pair detection with a timeout; see Queries.

Multiplexers

tmux passes Sixel through to the outer terminal when built with --enable-sixel (3.4)¹ and does not understand Kitty or iTerm2 images. The Kitty protocol's Unicode placeholders were designed for this case: the image is transmitted once through a passthrough sequence, then referenced with ordinary text cells that tmux can move and redraw.

Probe

stty -echo -icanon min 0 time 5
printf '\033[c'; dd bs=64 count=1 2>/dev/null | cat -v; echo   # look for ;4;
printf '\033_Gi=31,s=1,v=1,a=q,t=d,f=24;AAAA\033\\'
dd bs=64 count=1 2>/dev/null | cat -v; echo                    # expect i=31;OK
stty sane

Sources

• VT330/VT340 Programmer Reference, chapter 14
• kitty graphics protocol
• iTerm2 inline images

Compatibility

Feature support by terminal. Imported claims have not been reverified; unknown is not unsupported.

Feature / stable ID	Alacritty	Apple Terminal	ConPTY (conhost)	Contour	DomTerm	foot	Ghostty	iTerm2	kitty	Konsole	mintty	mlterm	PuTTY	Revenant	RLogin	st	tmux	rxvt-unicode	VTE	wayst	WezTerm	Windows Terminal	xterm	xterm.js
Sixel dcs-sixel	UnsupportedImported · unverified	Unknown	Unknown	SupportedImported · unverified	SupportedImported · unverified	SupportedImported · unverified	UnsupportedImported · unverified	SupportedImported · unverified	UnsupportedImported · unverified	SupportedImported · unverified	SupportedImported · unverified	SupportedImported · unverified	Unknown	Unknown	SupportedImported · unverified	Unknown	SupportedImported · unverified	Unknown	SupportedImported · unverified	Unknown	SupportedImported · unverified	SupportedImported · unverified	SupportedImported · unverified	SupportedImported · unverified
iTerm2 osc-1337-inline-images	UnsupportedImported · unverified	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	SupportedImported · unverified	Unknown	SupportedImported · unverified	SupportedImported · unverified	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	Unknown	SupportedImported · unverified	Unknown	Unknown	SupportedImported · unverified
Kitty apc-kitty-graphics	UnsupportedImported · unverified	Unknown	Unknown	PartialImported · unverified	Unknown	Unknown	SupportedImported · unverified	Unknown	SupportedImported · unverified	SupportedImported · unverified	Unknown	Unknown	Unknown	Unknown	Unknown	PartialImported · unverified	PartialImported · unverified	Unknown	Unknown	SupportedImported · unverified	SupportedImported · unverified	Unknown	Unknown	Unknown

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1. tmux CHANGES, 3.4. ↩