Sixel graphics

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Standard

Sixel graphics is a bitmap graphics protocol that encodes pixel data as sequences of printable ASCII characters, originally introduced in the DEC VT240 and VT340 terminals. The name "Sixel" refers to the encoding of six vertical pixels per character, forming a column of six bits.

Syntax

DCS P1 ; P2 ; P3 q [sixel-data] ST      Sixel graphics

Formal syntax

sixel          = 0x1b, "P", [ P1 ], ";", [ P2 ], ";", [ P3 ], "q",
               [ raster-attrs ], { sixel-line }, ( 0x1b, "\\" | 0x9c ) ;
P1             = digit, { digit } ;                   (* pixel aspect ratio selector; default: 0 *)
P2             = digit, { digit } ;                   (* background color mode: 0|1|2; default: 0 *)
P3             = digit, { digit } ;                   (* horizontal grid size; default: 0 *)
raster-attrs   = '"', Pan, ";", Pad, [ ";", Ph, ";", Pv ] ;
Pan            = digit, { digit } ;                   (* pixel aspect numerator *)
Pad            = digit, { digit } ;                   (* pixel aspect denominator *)
Ph             = digit, { digit } ;                   (* horizontal extent in pixels *)
Pv             = digit, { digit } ;                   (* vertical extent in pixels *)
sixel-line     = { sixel-item }, ( "$" | "-" ) ;
sixel-item     = color-intro | repeat-intro | sixel-char ;
color-intro    = "#", Pc, ";", Pu, ";", Px, ";", Py, ";", Pz ;
Pc             = digit, { digit } ;                   (* color register number *)
Pu             = "1" | "2" ;                          (* 1=HLS, 2=RGB *)
Px             = digit, { digit } ;                   (* hue or red *)
Py             = digit, { digit } ;                   (* lightness or green *)
Pz             = digit, { digit } ;                   (* saturation or blue *)
repeat-intro   = "!", count, sixel-char ;
count          = digit, { digit } ;
sixel-char     = ? 0x3F to 0x7E ? ;                   (* ASCII 63-126; encodes 6 vertical pixels *)
digit          = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;

Parameters

Parameter	Description	Default
P1	Pixel aspect ratio selector. 0 and 1 select a 2:1 aspect ratio (historical VT default); 2 selects 5:1; values 3-9 select other ratios. Modern terminals typically ignore this.	0
P2	Background color mode. 0 or 2: background pixels remain at their current color. 1: background pixels are set to color register 0.	0
P3	Horizontal grid size in decipoints. Typically ignored by modern terminals.	0

Raster attributes

The optional raster attributes command "Pan;Pad;Ph;Pv sets the pixel aspect ratio and declares the image dimensions before any sixel data is sent.

Parameter	Description
Pan	Pixel aspect ratio numerator
Pad	Pixel aspect ratio denominator
Ph	Horizontal extent (image width in pixels)
Pv	Vertical extent (image height in pixels)

Declaring Ph and Pv allows the terminal to allocate the correct buffer size up front, improving rendering performance.

Color introduction

The # command selects or defines a color register:

• #Pc -- Select color register Pc for subsequent sixel data.
• #Pc;Pu;Px;Py;Pz -- Define color register Pc. When Pu=1, the values are HLS (Hue 0-360, Lightness 0-100, Saturation 0-100). When Pu=2, the values are RGB (Red 0-100, Green 0-100, Blue 0-100).

Description

Sixel data encodes a bitmap image as a series of printable ASCII characters. Each sixel character (ASCII 63 through 126) represents a column of 6 vertical pixels, where the low 6 bits of (character - 63) determine which of the 6 pixels are turned on. For example, the character ? (0x3F) maps to 000000 (all off) and ~ (0x7E) maps to 111111 (all on).

The image is drawn in horizontal bands called scanlines, each 6 pixels tall. Within a scanline, characters are drawn left to right. Special control characters navigate within the image:

• $ (Carriage Return) -- Moves the drawing position back to the left edge of the current scanline. This allows overprinting the same scanline with additional colors.
• - (Line Feed) -- Moves the drawing position to the left edge and advances down to the next scanline (6 pixels lower).
• ! count char (Repeat) -- Repeats the sixel character char the specified number of times. For example, !10~ draws 10 columns of 6 fully-lit pixels.

The color model uses numbered color registers (typically 256 or more in modern terminals, though the VT340 supported 16). A typical sixel image interleaves color selection with drawing commands: select a color, draw pixels in that color, use $ to return to the start, select another color, draw its pixels, and so on for each scanline.

note

The VT340 supported only 16 color registers with RGB or HLS definition. Modern terminals commonly support 256 or more registers, and some allow arbitrary numbers of colors.

Examples

# Minimal red square (2x6 pixels)
printf '\ePq"1;1;2;6#0;2;100;0;0~~\e\\'

# 10x6 red block using repeat compression
printf '\ePq"1;1;10;6#0;2;100;0;0!10~\e\\'

# Two-color pattern: red and blue on the same scanline
printf '\ePq"1;1;4;6#0;2;100;0;0#1;2;0;0;100#0~~$#1??~~\e\\'

# Using raster attributes to declare a 100x60 image
printf '\ePq"1;1;100;60#0;2;100;0;0!100~-!100~-!100~-!100~-!100~-!100~-!100~-!100~-!100~-!100~\e\\'

Specifications

Specification	Section
VT330/VT340 Reference	—

Terminal support

Terminal	Support	Version	Notes
Terminal Emulators
Alacritty	✗	No	Not implemented
Bobcat	✓	0.9.0	Implemented via TerminalCtrl library
contour	✓	v0.1.0	Full implementation with SixelParser and SixelImageBuilder
foot	✓	1.2.0	Full sixel support with DCS implementation
Ghostty	✗	No
iTerm2	✓	v20260216-nightly	DCS_SIXEL token, VT100SixelParser
Kitty	✗	No
Konsole	✓	Yes	MODE_Sixel with processSixel implementation
mintty	✓	Yes	Full Sixel graphics support via DCS
mlterm	✓	rel-3_3_5	Full sixel support including animation
PuTTY	✗	No	DCS sequences recognized but explicitly ignored (terminal.c:3244-3246)
Rio	✓	v0.1.13
rxvt-unicode	✗	No	DCS handler discards all sequences
st	✗	No	DCS sequences recognized but not processed
terminology	✗	No	Stub handler only; not implemented
VT100	✗	No
VTE	✓	Yes	Requires WITH_SIXEL compile flag
WezTerm	✓	20200620-160318-e00b076c
Windows Terminal	✓	Yes	Full implementation with SixelParser class. DCS sequence handler in adaptDispatch.cpp
xterm	✓	xterm-294	Requires --enable-sixel-graphics compile flag
xterm.js	✓	0.1.1	Requires @xterm/addon-image addon. Supported since initial addon release.
Multiplexers
cy	✗	No
GNU Screen	✗	No	DCS sequences pass through without Sixel interpretation
tmux	✓	3.4	Requires ENABLE_SIXEL compile flag
tuios	✓	v0.6.0
Zellij	✓	v0.31.0

See also

• Kitty graphics protocol -- A modern alternative to Sixel with more features
• iTerm2 inline images -- Another inline image protocol