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https://github.com/hackerb9/lsix

Like "ls", but for images. Shows thumbnails in terminal using sixel graphics.
https://github.com/hackerb9/lsix

files graphics imagemagick ls montage sixel-graphics terminal terminal-graphics thumbnails vt340 xterm

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Like "ls", but for images. Shows thumbnails in terminal using sixel graphics.

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README 

        



# lsix

Like "ls", but for images. Shows thumbnails in terminal using [sixel](https://en.wikipedia.org/wiki/Sixel)

graphics.



## Usage



    lsix [ FILES ... ]



## Examples



### Basic Usage



Just typing `lsix` will show images in the current working directory.

You can also specify filenames and, of course, use shell wild cards

(e.g., `lsix *jpg *png`).



Because lsix uses ImageMagick pretty much any image format will be

supported. However, some may be slow to render (like PDF), so lsix

doesn't show them unless you ask specifically. If you want to force a

listing of a certain type of image simply specify the filenames or

use a wildcard (`*.pdf` in the example below),.



![Example 1 of lsix usage](/README.md.d/example1.png "Most basic usage")



### Expanding GIFs 

If you specify a GIF (or actually any file that has multiple images in

it) on the command line, all the frames will get expanded and shown in

a montage. For example, `lsix nyancat.gif` shows all the frames. Note

that GIF stores some frames as only the pixels that differ from the

previous frame.

![Example 2 of lsix usage](/README.md.d/example2.png "GIFs get expanded")



### Terminal background color is detected



You may have noticed that PNGs and SVG files have correct alpha

channel for the terminal background. That is because lsix uses

terminal escape sequences to try to figure out your foreground and

background colors. (Foreground is used for the text fill color.)



In the first example below, after running `lsix` in a white on black

xterm, I sent an escape sequence to swap foreground and background

colors. When I ran it again, `lsix` detected it and changed the

background color to white. Of course, you can pick whatever default

colors you want (e.g., `xterm -bg blue`, in the second example below).



![Example 3 of lsix usage](/README.md.d/example3.png "Reverse video works")

![Example 4 of lsix usage](/README.md.d/example4.png "Even 'xterm -bg blue' works")



## Features



* Detects if your terminal can display SIXEL graphics inline using [control sequences](https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h2-Sixel-Graphics).



* Works great over ssh. Perfect for manipulating those images on the

  web server when you can't quite remember what each one was. 



* Non-bitmap graphics often work fine (.svg, .eps, .pdf, .xcf).



* Automatically detects if your terminal, like xterm, can increase the

  number of color registers to improve the image quality and does so.



* Automatically detects terminal's foreground and background colors.



* In terminals that support dtterm WindowOps, the number of tiles per

  row will adjust appropriately to the window width.



* If there are many images in a directory (>21), lsix will display them

  one row at a time so you don't need to wait for the entire montage

  to be created.



* If your filenames are too long, lsix will wrap the text before

  passing it into ImageMagick's `montage`. (Without lsix, `montage` just

  jumbles long filenames on top of one another.)



* You can easily change things like the width of each tile in the

  montage, the font family, and point size by editing simple variables

  at the top of the file. *(Tip: try `convert -list font` to see what

  fonts you have on your machine.)*



* Unicode filenames work fine, as long as your font has the glyphs.



## Installation



Just put the [`lsix`](/lsix) file in your path (e.g., /usr/local/bin) and run

it. It's just a BASH shell script.



The only prerequisite software is ImageMagick. If you don't have it

yet, your OS's package manager will make it easy to get. (E.g.,

`apt-get install imagemagick`).



MacOS users may prefer to install lsix using `brew install lsix` which

installs ImageMagick, if necessary.



## Your Terminal must support Sixel graphics



I developed this using [xterm](https://invisible-island.net/xterm/) in

vt340 emulation mode, but I believe this should work on

any Sixel compatible terminal. You may test your terminal by viewing a

single image, like so:



    convert  foo.jpg  -geometry 800x480  sixel:- 



### XTerm



Note that xterm does not have Sixel mode enabled by default, so you

need to either run it like so:



    xterm -ti vt340



Or, make vt340 the default terminal type for xterm. Add the following

to your `.Xresources` file and run `xrdb -merge .Xresources`.



    ! Allow sixel graphics. (Try: "convert -colors 16 foo.jpg sixel:-").

    xterm*decTerminalID	:	vt340

    

Further, some distributions, such as Fedora, appear to not compile `xterm`

with sixel support. In that case, try an alternate terminal, such as

`foot` or `mlterm`.



### SIXEL compatible terminals



* XTerm (tested)

* MLterm (tested)

* foot (tested)

* Wezterm (tested)

* Contour (tested)

* iTerm2 for Apple MacOS (tested)

* Konsole (reported)

* yakuake (reported)

* WSLtty for Microsoft Windows (reported)

* MinTTY for Cygwin (Microsoft Windows) (reported)

* Yaft for Linux framebuffer (tested)

* VTE (special compilation, reported)

* sixel-tmux (fork of tmux, reported)

* ttyd (reported)



### SIXEL incompatible terminals



* MacOS Terminal, kitty

* All standard libvte based terminals

  * gnome-terminal

  * terminator

  * lxterm

* Alacritty (might work with [a patch](https://github.com/alacritty/alacritty/pull/4763))



## Configuration



Because `lsix` is currently designed to be very simple, there are no

command line flags, no configuration files, no knobs to twiddle, or

frobs to frobnosticate. However, since the script is so simple, if you

want to make a change, it's pretty easy to do just by editing the

file. Everything is nicely commented with the most common default

variables at the top.



## Contact the author



I welcome feedback. If you use lsix and like it or have suggestions

for how it can be improved, please go ahead and send your thoughts to

me [@hackerb9](https://github.com/hackerb9/lsix/issues/new) via

GitHub.



## Bugs



* XTerm's reverse video mode (`xterm -rv`) is different from

  specifying the foreground and background explicitly. There is a way

  to detect the latter, but not the former. That means the background

  color will be incorrect for folks who use XTerm's reverseVideo

  resource. (See issue #20).



* XTerm's screen width is currently limited to 1000px due to a

  misfeature which causes it to silently show nothing. This limitation

  will be removed once xterm can handle images greater than 1000x1000.

  [Last tested with XTerm(344)].



* Filenames that begin with "@" are special to ImageMagick and it'll

  freak out if you don't prepend a directory. (`lsix ./@foo.png`)

  (This is a bug in ImageMagick, not lsix).



* Specifying the empty string `""` as a filename makes ImageMagick hang.

  (This appears to be an ImageMagick bug / misfeature). 



* Long filenames are wrapped, but not intelligently. Would it

  complicate this script too much to make it prefer to wrap on whites

  space, dashes, underscores, and periods? Maybe.



* Directories specified on the command line are processed as if the

  user had cd'd to that directory. It wouldn't be hard to implement

  recursion, but is there actually a need? I'm reluctant to complicate

  such a simple script with command line flags.



* If you run `lsix foo.avi`, you're asking for trouble.



## Future Issues



* The Sixel standard doesn't appear to have a way to query the size of

  the graphics screen. Reading the VT340 documentation, it appears

  your program has to already know the resolution of the device you're

  rendering on.



  XTerm, as of version 344, has added [a control

  sequence](https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h2-Functions-using-CSI-_-ordered-by-the-final-character_s_)

  that solves the problem — `CSI ? Pi ; Pa ; Pv S` — but some

  terminals, for example `mlterm`, haven't yet implemented it.



  There is an alternate way to read the window size using the dtterm

  WindowOps extension but it is not quite the right solution as the

  geometry of the Sixel graphics screen is not necessarily the same as

  the window size. (For example, xterm limits the graphics geometry to

  1000x1000, even though the window can actually be larger.) To help

  with terminals such as mlterm, `lsix` will use the dtterm WindowOps

  as a fallback.



  If neither solution works, `lsix` will assume you are on a VT340

  (800x480) and can fit only 6 tiles per row.



* The Sixel standard also lacks a way to query the number of

  color registers available. I used the extensions from `xterm` to do

  so, but I do not know how widely implemented they are. If a terminal

  does not respond, `lsix` presumes you're on an original vt340 and

  uses only 16 color registers. (Sorry, 4-gray vt330 users! Time to

  upgrade. ;-) )



* The [Kermit project](https://kermitproject.org/) created a MS-DOS

  terminal emulator that was popular in the late 1980s/early 1990s.

  Its sixel implementation is not compatible with lsix because it

  shows the graphics on a screen separate from the text. However, I

  noticed one feature in its documentation: an escape sequence to

  request the current graphics window size and number of colors:



```

 ESC [ ? 256 n                  Request screen size report



        Report is ESC [ ? 256; Ph; Pw; Pc n     for graphics systems



        where   Ph is screen height in dots

                Pw is screen width in dots

                Pc is number of colors (0, 1 or 16, for none, b/w, ega/vga)



        Report is ESC [ ? 24; 80; 0 n  for pure text mono systems.

```



  Did any other terminal emulators ever use the sequence? Would it be

  worthwhile to add to `lsix`?



* [libsixel](https://github.com/saitoha/libsixel) is an excellent

  project for writing programs that can output optimized Sixel

  graphics commands. Because I have a lot of respect for the project,

  I feel I should explain why `lsix` does not use libsixel.



  * (a) I wanted lsix to work everywhere easily. Bash and imagemagick

    are ubiquitous, so a shell script is a natural solution.



  * (b) I wanted `lsix` to be simple enough that it could be easily

    customized and extended by other people. (Including myself.)



  * (c) ImageMagick has better support for reading different formats

    than stb_image (the library used by libsixel's `img2sixel`). (For

    example: xpm, svg, 16-bit png, and even sixel files are not

    recognized by img2sixel). Since ImageMagick can read all of those

    and write sixel output directly, it made sense to use it for both.



  * (d) While libsixel is optimized and would surely be faster than

    ImageMagick, it's overkill. For a simple directory listing, this

    is plenty fast enough.



## Resources



  * [XTerm Control Sequences](https://invisible-island.net/xterm/ctlseqs/ctlseqs.html)

  * [ImageMagick](https://imagemagick.org/)

  * [VT340 Programmer's Reference](https://vt100.net/docs/vt3xx-gp/):

    * [Chapter 14](https://vt100.net/docs/vt3xx-gp/chapter14.html). Sixel Graphics.

    * [Chapter 16](https://vt100.net/docs/vt3xx-gp/chapter16.html#S16.3) Difference between Level 1 and Level 2 Sixel implementations.

        

        _Nota bene: this reference has the sense for DECSDM (sixel

        display mode) reversed! The actual behaviour of the VT340 is

        that when DECSDM is reset (the default), sixel scrolling is enabled.

        This can be done by sending _`Esc[?80l`_, but lsix does not do

        so as it would break many current terminal emulators.

        See issue #41 for details._



  * [DEC STD 070 Video Systems Reference Manual](https://archive.org/details/bitsavers_decstandar0VideoSystemsReferenceManualDec91_74264381).

    A weighty tome which covers nearly everything in exacting detail. I referred mostly to sections 4 (escape sequences) and 9 (sixel programming).



  * [VT340 Test](https://github.com/hackerb9/vt340test), a project to document the actual behaviour of the DEC VT340 hardware.



  * [Digital ANSI-Compliant Printing Protocol: Level 2 Programming Reference Manual](http://www.vaxhaven.com/images/f/f7/EK-PPLV2-PM-B01.pdf), Chapter 5: Sixel Graphics. An excellent and reasonably clear discussion for anyone who wants to generate or parse sixel graphics.