* bug#54514: incorrect arithmetic in color-lighten-hsl?
@ 2022-03-21 23:31 Noah Friedman
2022-03-22 14:28 ` Lars Ingebrigtsen
0 siblings, 1 reply; 2+ messages in thread
From: Noah Friedman @ 2022-03-21 23:31 UTC (permalink / raw)
To: 54514
(Any branch or release; this function in color.el looks to be unchanged
since it was originally introduced)
I might be mistaken, but I think color-lighten-hsl is wrong. It's
increasing luminance by an absolute percent of 1, not the present
luminance.
Suppose you want to lighten the color "red":
(color-name-to-rgb "red")
=> (1.0 0.0 0.0)
(color-rgb-to-hsl 1.0 0.0 0.0)
=> (0.0 1.0 0.5)
If you try to lighten this by, say, 50%, currently the result is
(color-lighten-hsl 0.0 1.0 0.5 50)
=> (0.0 1.0 1.0)
Which is clearly wrong. 50% lighter red is not white!
The result I would have expected to see is
=> (0.0 1.0 0.75)
Currently, the function reads:
(defun color-lighten-hsl (H S L percent)
...
(list H S (color-clamp (+ L (/ percent 100.0)))))
I think it should be:
(defun color-lighten-hsl (H S L percent)
...
(list H S (color-clamp (+ L (* L (/ percent 100.0))))))
Could someone sanity check me? My color theory background is pretty weak.
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2022-03-22 14:28 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2022-03-21 23:31 bug#54514: incorrect arithmetic in color-lighten-hsl? Noah Friedman
2022-03-22 14:28 ` Lars Ingebrigtsen
Code repositories for project(s) associated with this public inbox
https://git.savannah.gnu.org/cgit/emacs.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).