Sixel is great. But you could also interpret the headers of common image file formats as terminal escape sequences, so that you can directly "cat lena.png" and see the image. Now, that would be a real hack!
The terminal couldn't do that as it wouldn't know the difference between a user typing `cat lena.png` into Bash from typing the same sequence of characters into vim (for example).
This is why there are separate commands like `icat` which will output ANSI escape sequences for rendering a PNG. Unfortunately a great many of these are terminal specific (iterm, terminology, kitty and VT200/VT300 (sixel) all have their own unique escape sequences. The closest to a standard we have is sixel and, frankly, I don't think it's that good on modern systems[1]). So you end up with different command for each "standard" you want rendered.
The approach I've taken in my own $SHELL is to have a builtin command like `cat` (I call it `open`) and that auto-detects which terminal emulator you're running and picks the right encoding to match what is supported by the terminal (if no standard can be auto-detected, then it falls back to ANSI art using coloured blocks). However the issue with that is now people need to run new custom shell instead Bash / Zsh / whatever. But the logic behind the auto-detection is really quite simple so that could be written it's own standalone tool.
[1] sixel re-encodes images in character blocks of 6 pixels. Where as iTerm, Kitty and Terminology send the image as is over the terminal via a base64 encoded string. All those solutions are inlined via ANSI escape sequences though.
> The terminal couldn't do that as it wouldn't know the difference between a user typing `cat lena.png` into Bash from typing the same sequence of characters into vim (for example).
This is not what I am talking about. I mean the binary headers inside png, jpg, tiff files, etc. These binary sequences can be easily interpreted as terminal control sequences, and they are very unlikely to appear otherwise. For pnm files I agree that the situation is a bit more delicate, as these sequences are likely to appear in the wild (e.g., in the pnm man page for example).
This is an inevitable feature of the perfect terminal. The alternative is showing the binary contents of the image file in ASCII, which is always undesired.
Not just undesired; it can sometimes play havoc with your terminal session. I've had tmux status bars break; bash prompts go "weird" and all sorts of other glitches before when I've accidentally piped binary data to the STDOUT.
I'm very tempted to fork Aminal and have a play with your idea.
That would be lovely! I do a lot of image processing using unix pipes, and when I forget the "|display" at the end it breaks everything.
Notice that you do not even need to use sixels in your case. Since you control the rendering, you can simply put the pixels of the image on a rectangle (that allows paning and zooming, for example), and move the cursor below it.
It wouldn't be until I'm off for Christmas holidays (at the earliest) though. I don't have a whole lot of time left between work and family; and have a few projects on the go as it is already.
