SIXEL File Format (.sixel)

A SIXEL file holds a bitmap encoded entirely as printable ASCII characters, using DEC's six-pixel-tall encoding scheme, so it can be sent to a printer or terminal over a plain 7-bit serial link and displayed without any separate image protocol.

.sixelImage Files

SIXEL at a glance#

Full name	DEC SIXEL Graphics Format
File extension	.sixel
Category	Image Files
Developer	Digital Equipment Corporation (DEC)
First released	1983
Compression	Lossless
FileFlip support	FileFlip writes this format but cannot open one

What a .sixel file can hold#

These are the things a SIXEL file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.

Embedded metadata	No
Colour profiles	No
Multiple images or pages	No
Human readable	Yes

Strengths and limitations of SIXEL#

What SIXEL does well

Draws directly inside a terminal's own text stream as printable characters, so it passes through SSH and tmux without a dedicated image protocol
Was designed from the start to survive 7-bit serial links, which is exactly why every pixel maps to a plain ASCII character
Renders instantly in the growing list of terminal emulators that added support during Sixel's recent revival, including xterm, foot, mlterm, WezTerm and Konsole

Where SIXEL falls short

Still unsupported in several mainstream terminals, including iTerm2, which shows the raw escape sequence as text instead of an image
Limited to a reduced colour palette historically capped at 256 colours, so photographic images need dithering to look reasonable
Has no compression beyond the encoding itself, so a Sixel image is far larger on disk than an equivalent PNG

Use Sixel when an image needs to display inline inside a terminal session, such as showing a chart or a thumbnail over SSH without opening a separate viewer.

Convert a Sixel image to PNG once it needs to be viewed anywhere outside a terminal emulator that understands the encoding.

How to open a .sixel file#

A .sixel file opens in the programs below, grouped by the platform you are on.

Platform	Programs that open it
Windows	WezTerm, mlterm
macOS	WezTerm, mlterm
Linux	xterm, foot, mlterm, Konsole
Web	FileFlip

SIXEL questions people ask#

What is a SIXEL file?

A SIXEL file is a bitmap image encoded as printable ASCII text using DEC's six-pixel-tall scheme, originally built in the early 1980s so DEC printers and terminals could receive graphics over the same serial link used for plain text.

Which terminals support Sixel graphics?

Terminal emulators including xterm, foot, mlterm, WezTerm and Konsole render Sixel images inline. Support is not universal: iTerm2 and several other popular terminals still show the raw Sixel escape sequence as garbled text instead of an image.

Why is Sixel showing up in terminals again?

Sixel was largely dormant once DEC's own terminal hardware disappeared, but modern terminal emulators revived it because it needs no custom protocol: the whole image is plain text inside a standard escape sequence, so it works over SSH and tmux the same way any other terminal output does.

Converting SIXEL files#

FileFlip cannot open a .sixel file, so there is nothing to convert it into here. It appears on the site as something other formats can be converted to.

Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.