Do not upscale picture

[ploum]

By default, displaying a picture with Chafa takes the whole terminal.

It would be nice to not upscale smaller pictures so the user can get a sense of the size of the picture (for example if it is an icon).

The "does not upscale" option could work together with the size option to set the size as "maximal size". If I set the size to 100 but I’m viewing an icon which is 10x10, the icon stays at 10x10.

[hpjansson]

Chafa doesn't actually take the whole terminal by default. You can see this with a tiny image (something like /usr/share/icons/Adwaita/16x16/devices/computer.png). However, it does upscale quite a bit to keep images legible when rendered with symbols: 1 horizontal pixel becomes 1 horizontal cell. The vertical size depends on font ratio, 1/2 by default. So a 16x16 image becomes 16x8 cells.

If we try to map it to something closer to the actual pixel size, it would likely take up only 1 or 2 cells, which would make it unrecognizable. One could argue that we could use a smaller size when there is a pixel-perfect alternative (sixels/kitty/iterm), but I think it's nice to produce a consistent screen size across all protocols...

[ploum]

I understand the point when the rendering is not pixel-perfect. My request was initially done with pixel-perfect renderers in mind (I should have clarified that). A good test is to render, in Kitty, chafa-logo.gif with both timg and chafa. Chafa result is twice the size of timg result with some decreased visibility (as you are now zoomed in on a pixelated animation). I don’t have a perfect solution here. What I realize, as a end user is that I prefer original size when pixel perfect rendering is used and clearer possible output otherwise. (well, this last point is quite debatable in my own case because if I know that the rendering is small, it usually means that it’s an icon and I should not really care about it). Thinking out loud here: I would be interested to try a kind of "never-upscale" option that would use size only as a higher limit. I would be really curious to see what it does in Offpunk as, currently, important pictures are rendered the same size as small icons (which are, hopefully, most of the time removed by python-readability).

[hpjansson]

This is somewhat complicated by the fact that the Chafa API expresses dimensions in terms of cells, so some scaling (and aspect distortion) will happen no matter what. At smaller sizes, the relative distortion is greater. That is, the lost fraction is a greater portion of the total (e.g. rounding 2x2.5 to 2x3 results in greater distortion than rounding 40x40.5 to 40x41). So: Making images tiny can also make them kind of ugly.

Regarding a maximum size, there is currently such a thing, although it's not directly controllable. It's taken from the detected terminal size (falling back to 80x25 if detection fails). It could make sense to allow direct control of that.

Here's what I think we could do:

• Introduce a --scale <num> parameter taking a decimal number. It would default to 8.0 (current behavior) or maybe 4.0. Passing --scale 1 would do what you want. The existing --size parameter would override it if both are specified.
• Introduce a --frame-size NxM parameter to specify the maximum size in cells. This would override the detected terminal size. The resulting image could be smaller, as determined by the scaling factor, but not bigger than this. Again --size would override, producing a bigger image.

I think this would do what you want and give some extra flexibility too. And it preserves existing behavior. What do you think?

Edit: Actually, --size currently acts like --frame-size described above. I'd be changing its behavior to force the image dimensions, but still respect aspect unless --stretch was passed.

[ploum]

This looks like a good idea but what would happen if I give --scale=1 and the resulting picture is bigger than the max size ? If I understand correctly, --size overide --scale. Thus adding a --size makes the --scale useless, right? Also, how would it works with pixel-perfect rendering such as Kitty-protocol? (I realize it’s a hard problem, so it might be interesting to see if there are other usecases like mine or if I’m wrong about what I think I want).

[hpjansson]

Correct, --scale would respect the max size (terminal window or --frame-size). --size always wins, it'd override everything.

It would work the same with pixel-perfect (or near-perfect) rendering; it'd cover the same number of cells as the symbol output does (keeps it predictable).

[ploum]

I’m a bit confused with all those options.

How would I say "makes it natural size except if it’s bigger than the terminal, in which case resize to the terminal size" ?

[hpjansson]

--scale would respect the terminal's size. So you'd only need --scale 1, nothing else.

[ploum]

Then it’s perfect for my needs :-)

[hpjansson]

The 1.12.0 release now has the --scale <n> option!