Re: CSS contrast (#30295) (was Re: Heads-up: Emacs 26.1 RC1)

[Richard Copley]

On 21 March 2018 at 09:59, Richard Copley <address@hidden> wrote:

On 21 March 2018 at 07:38, Eli Zaretskii <address@hidden> wrote:

> From: Richard Copley <address@hidden>
> Date: Tue, 20 Mar 2018 19:56:12 +0000
> Cc: John Wiegley <address@hidden>, Tom Tromey <address@hidden>,
>       Emacs Development <address@hidden>
>
> Patch 1 is a small fix for the current formula using color-distance.
> Patch 2 uses luminance as in Tom's original patch.
> I think patch 2 gives better contrast.

Thanks, but I think this is a step backward, as it more or less goes
back to the code before the discussion of bug#25525.

Patch 2 does, yes. It's good to step backwards, because (the effect of) the original code was OK, whereas the current code leads to unreadable text.

How about making the threshold a customizable value instead, with the
current hard-coded value the default?  That'd be compatible, and
should allow you to get the contrast of your liking.

It sounds like you want to insist that white-on-pale-green is somehow better than black-on-pale-green, or that there's some other consideration that's more important.

I don't understand.

To put it another way:

Your argument seemed to be that Tom's original criterion (use white text on backgrounds with luminance <50%) was invented by Tom.
Is the current criterion (use white text on backgrounds inside a sphere of a given radius centred on black, in the color-distance metric space) a standard way of doing things?

I'm not saying that the luminance-less-than-50% calculation is a standard, either, but I've seen it used before, which is more than I can say for the color-inside-a-sphere calculation.

I'm also not saying that color-distance is any more or less "invented" than luminance.

I do believe that color-distance is less relevant here than luminance is.

I also believe that black text is more readable than white text, on a pale green background.