Re: [gnus git] branch master updated: =1= shr.el (shr-tag-div): Added.

[Julien Danjou <julien@danjou.info>]

On Sun, Nov 21 2010, Lars Magne Ingebrigtsen wrote:

> It sounds good; when it's published I'll try reinstating the colour
> stuff in shr and give it a whirl.

I've published things here:
http://git.naquadah.org/?p=~jd/color-el.git;a=summary

Here's a snippet you can use to test it after loading color.el

--8<---------------cut here---------------start------------->8---
(with-current-buffer (switch-to-buffer-other-window (get-buffer-create "*color test*"))
  (erase-buffer)
  (dotimes (i 100)
    (let* ((entry (cons
                   (nth (random (length (x-defined-colors))) (x-defined-colors))
                   (nth (random (length (x-defined-colors))) (x-defined-colors))))
           (color1 (apply 'rgb->lab (mapcar (lambda (x) (/ x 65535.0)) (x-color-values (car entry)))))
           (color2 (apply 'rgb->lab (mapcar (lambda (x) (/ x 65535.0)) (x-color-values (cdr entry)))))
           (luminance-ratio (/ (abs (- (car color1) (car color2))) (+ (car color1) (car color2))))
           (distance (ciede2000 color1 color2)))
      (insert (propertize
               (format
                "%s distance %f luminance-ratio %f: %s and %s\n"
                (if (and (> distance 6)
                         (> luminance-ratio 0.09))
                    "GOOD! :-)"
                  "BAD")
                distance luminance-ratio
                (car entry) (cdr entry))
               'face `(:background ,(car entry) :foreground ,(cdr entry))))))))
--8<---------------cut here---------------end--------------->8---

`ciede2000' returns the distance between 2 colors. I don't know what the
JND[1] threshold value for this algorithm, but 6 does not seems too bad.

For the luminance of a color, the value is stored in the L component of
the Lab format, so it's the car of what 'rgb->lab returned. I compute a
ratio, but feel free to invent something better!

I think both color distance and luminance have to be checked. I tried
several check threshold, with special case if the background is darker
than the text, but did not found anything very effective.

Feel free to try to find something and to ask me question if you need.
:)

[1]  Just Noticeable Difference

-- 
Julien Danjou
// ᐰ <julien@danjou.info>   http://julien.danjou.info