Subject: Re: FVWM: Re: Colormap issues

From: Olivier Chapuis <[email-masked]>
Date: Wed, 2 Oct 2002 00:41:25 +0200

I switch to the workers list.

On Tue, Oct 01, 2002 at 06:03:56PM -0400, Dan Espen wrote:
> 
> I think we still need to work out what the new default should be.
>

Yes, but I am afraid that there is no good default (but when
someone choose for us as XRender do). I think the good default
depends on the applications the user use.

> 
> Olivier,  I don't know if that will help, for one thing it will use
> up more colors.  I don't know if we discussed this before, but
> the 61 color table had a lot of colors in it that were designed to
> evenly fill the gaps in the perceptual (HVC) colorspace.
> I believe the new
> tables are optimized for gradients by spacing the colors evenly in
> a linear colorcube.  That can leave some pretty big gaps in
> the perceptual colorspace.
> 

Yes linear colorcube are not so good. At least I can see the grey
colors gap. XRender solve this problems by adding some (but do not
dither).  Linear colorcubes are good for fast pointwise dithering (and
not so catastrophic visually). I've read some papers this day on
dithering and there are methods for dithering with an arbitrary colors
map but not in "real time" (this is maybe not an obstruction with
colorsets). So if we can find the gaps, we can either discover a new
dithering method with the lcc + the gaps or use the lcc when dithering
is needed and the lcc + the gaps if not.

> Thats not to say that the 61 color color table won't turn gray
> into pink or green, I've seen it do that.
> 
> I don't know if we discussed any color theory before, I hope this
> stuff makes some sense to you (perceptual and linear colorspaces).
> I'm not a color expert, but I did some
> study of this stuff when I came up with the original 61 colors
> and the matching algorithm.  The matching algorithm in Fvwm is
> not the algorithm used to create the 61 color color table, since
> the perceptual match algorithm is too slow for Fvwm use.
> 
> I still have the source code for the program I used to fill in
> the gaps if you're interested.
> 

Yes of course I am really interesed! If you know some articles or good
links on the subject I am intersed too.

Olivier
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---

From: Dan Espen <[email-masked]>
Date: Wed, 02 Oct 2002 09:36:46 -0400

Olivier Chapuis <[email-masked]> writes:
> Yes of course I am really interested! If you know some articles or good
> links on the subject I am interested too.

You might start here:

http://www.inforamp.net/~poynton/Poynton-colour.html

There are quite a few links there.

I spent a year or 2 reading sci.engr.color (usenet).

I'll send you the source separately.

-- 
Dan Espen                           E-mail: [email-masked]