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Re: CIE color definitions in CSS3 color module

From: Alan Gresley <alan@css-class.com>
Date: Sat, 18 Sep 2010 09:17:59 +1000
Message-ID: <4C93F727.9040702@css-class.com>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
CC: Alexis Shaw <alexis.shaw@gmail.com>, www-style@w3.org
Tab Atkins Jr. wrote:
[snip]
> Returning to the core of the issue; what's the use-case for these new
> ways of defining a color?  I know that various other color definitions
> *exist*, but I don't understand what they're used for, or if they're
> useful for the web.  Could you elaborate on this?


To display more of the colors that people can see on a future display 
device.

I previously said this in this thread.

   | If such a limited gamut of sRGB color-space can produce
   | 16,777,216 values or 16,777,215 colors (minus black),
   | this far exceeds the the average 10 million that a person
   | can observe in theorized xyz color space.


What I didn't say was that sRGB only contains about half or even a 
third of the colors that people can perceive. About 5 or 7 million 
colors can not be seen on current display devices.

I can't create colors which I used with oil paint. These are Cadmium 
Red, Cobalt Blue, Magenta, Brilliant Green. The greens are the most 
prominent colors that are missing from a RGB color space pallet.

Already we have cameras that have a larger gamut than RGB color space. 
Some of these images can be manipulated with various programs. The 
only problem is that the OS (ie. Window 7), lest any UA tired to such 
system can not shows these missing colors.

Also, why not allow a display device to show ultra-violet.

> Note, as well, that CSS generally assumes that colors exist in the
> sRGB colorspace, and defines interpolation for things like transitions
> and gradients in terms of that space.
> 
> ~TJ


Yes, that is the challenge, it is not simple algorithms. For CIE xy 
chromaticity space and CIE xyY color space [1] we see this.


   | If one chooses any two points of color on the chromaticity
   | diagram, then all the colors that lie in a straight line
   | between the two points can be formed by mixing these two
   | colors. It follows that the gamut of colors must be convex
   | in shape. All colors that can be formed by mixing three
   | sources are found inside the triangle formed by the source
   | points on the chromaticity diagram (and so on for multiple
   | sources).


   | The diagram represents all of the chromaticities visible to
   | the average person. These are shown in color and this region
   | is called the gamut  of human vision. The gamut of all
   | visible chromaticities on the CIE plot is the tongue-shaped
   | or horseshoe-shaped figure shown in color. The curved edge
   | of the gamut is called the spectral locus and corresponds to
   | monochromatic light, with wavelengths listed in nanometers.
   | The straight edge on the lower part of the gamut is called
   | the line of purples. These colors, although they are on the
   | border of the gamut, have no counterpart in monochromatic
   | light. Less saturated colors appear in the interior of the
   | figure with white at the center.



1. 
<http://en.wikipedia.org/wiki/CIE_1931_color_space#The_CIE_xy_chromaticity_diagram_and_the_CIE_xyY_color_space>

-- 
Alan http://css-class.com/

Armies Cannot Stop An Idea Whose Time Has Come. - Victor Hugo
Received on Friday, 17 September 2010 23:18:33 GMT

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