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From: Eli Zaretskii <eliz@gnu.org>
To: "Gerd Möllmann" <gerd.moellmann@gmail.com>,
	"Julien Danjou" <julien@danjou.info>,
	"Mattias Engdegård" <mattiase@acm.org>
Cc: Noah Friedman <noah@splode.com>, 74055@debbugs.gnu.org
Subject: bug#74055: 31.0.50; color-lighten-name not lightening black
Date: Mon, 28 Oct 2024 14:39:17 +0200	[thread overview]
Message-ID: <86plnk766i.fsf@gnu.org> (raw)
In-Reply-To: <m2wmhsk4y6.fsf@gmail.com> (message from Gerd Möllmann on Mon, 28 Oct 2024 09:27:29 +0100)

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Date: Mon, 28 Oct 2024 09:27:29 +0100
> 
> The function color-lighten-name doesn't work as I would expect for
> black:
> 
>   (color-lighten-name "#000000" 50)
>   => "#000000000000"
> 
> I think there is even a test that checks that, in color-tests.el:
> 
> (ert-deftest color-tests-lighten-name ()
>   (should (equal (color-lighten-name "black" 100) "#000000000000"))
> 
> I don't understand this, and it is different from what I'd expect, and
> tools for the web return, for example
> 
>   https://mdigi.tools/lighten-color/#000000

Our notion of "lighten color" seems to be to increase the color's
luminance by P percent.  Since the black color's luminance is zero,
increasing that by 50% still yields zero.

By contrast, the page you point to seems to interpret "lighten" to
mean that P is the percentage of the full scale, not of the original
color's luminance.

This goes back to commit 656c2dd66e, which was supposed to fix
bug#54514.  But maybe Noah's interpretation of "lighten" was
incorrect, and we should revert that change?  OTOH, if we do revert
it, then Noah's example will disagree with the above page.

So I guess our algorithm is incorrect somewhere?

Adding Julien and Mattias, in the hope that they could help unconfuse
us.





  reply	other threads:[~2024-10-28 12:39 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-10-28  8:27 bug#74055: 31.0.50; color-lighten-name not lightening black Gerd Möllmann
2024-10-28 12:39 ` Eli Zaretskii [this message]
2024-10-28 15:18   ` Ship Mints
2024-10-28 16:57   ` Mattias Engdegård
2024-10-28 17:24     ` Eli Zaretskii
2024-10-29  4:41       ` Gerd Möllmann
2024-10-29  8:25         ` Gerd Möllmann
2024-10-29 12:54       ` Mattias Engdegård
2024-10-29 18:27         ` Gerd Möllmann

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