вс, 7 мар. 2021 г. в 23:46, Alan Third <alan@idiocy.org>:

> On Sun, Mar 07, 2021 at 10:12:43PM +0300, Evgeny Zajcev wrote:
> > Currently, image transformation for upscaled images uses NEAREST filter,
> > which is fast, but renders very bad results for images with text inside.
> >
> > Maybe change it to GOOD, which is also fast, but renders more decent
> results
> >
> > Here is I've got two screenshots showing the difference:
> >
> > NEAREST (currently hardcoded in Emacs) -
> > http://lgarc.narod.ru/pics/upscaled-nearest.png
> >
> > GOOD (my proposal) - http://lgarc.narod.ru/pics/upscaled-good.png
> >
> > What do you think?
>
> See also bug#38394.
>
> The reason nearest was chosen was because scaled up pixel art (emojis,
> mostly, like etc/images/smilies/wry.xpm) looked abominable


In 2k21 any xpm with any filter will look abominable :)

when using
> the "best" filter,



> but most other types of images look OK when using
> nearest.


We (telega.el project) see many images of different kind daily, and only
some of them looks OK when nearest filter is applied. Most of the time,
especially if some contrast diagonals are involved (including character
glyphs) upscaling results are no ok.  Also, doc-view suffers from this,
most pdf files viewed inside Emacs looks no ok.

On the other hand the bug report complains that scaled up
> pixel art looks abominable with nearest, so clearly there's a
> difference of opinion.
>

Just get rid of any xpm :) Emacs has nice support for SVG after all, we can
write xpm to svg converter to keep pixel art precision.

I don't know whether "good" is a better compromise, I suspect it looks
> quite like "best".
>
I don't know what the best option is, I suspect there's no clear
> one-size-fits-all winning strategy.
>

Or maybe we can make the transformation filter configurable, so it could be
changed from elisp side?

-- 
lg