W3C home > Mailing lists > Public > www-style@w3.org > September 2010

Fwd: Re: CIE color definitions in CSS3 color module

From: <alexis.shaw@gmail.com>
Date: Sat, 18 Sep 2010 02:01:07 +0000
Message-ID: <00163646ca7875e45a04907f0dc1@google.com>
To: "www-style@w3.org list" <www-style@w3.org>
> The new HP displays at the moment already can display Adobe RGB, so that  
> is
> really an issue right now, I think that rather than changing a gamut to  
> allow one
> to use those colors, you should implement the CIE colors.

> There is a good way to convert it to sRGB as sRGB is defined over the XYZ  
> color system.
> it is no different than adobe RGB or any other color system. We just need  
> to define a way
> to clamp the colors. The obvious way to do so is to use the lab color  
> space with the D65 white point

> and find the color that has the smallest distance between the color to be  
> displayed and the bounding volume of the display.
> Also note that Firefox, Safari and chrome already have to deal with the  
> XYZ and Lab
> color spaces in order to ensure that the colos actually are sRGB. In that  
> regard implementation

> should not be difficult.

> On 18 September 2010 09:25, Tab Atkins Jr. jackalmage@gmail.com> wrote:


> On Fri, Sep 17, 2010 at 4:17 PM, Alan Gresley alan@css-class.com> wrote:

> > 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.





> I would much rather wait for a hypothetical future display device to

> become real before trying to address its needs. Engineering to meet

> predicted future needs has a generally poor track record on the web.






> >> 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>








> If there's no simple algorithm to convert from CIE spaces to sRGB,

> then this is dead in the water, isn't it? Browsers work with colors

> in sRGB. You can sometimes specify colors that officially lie outside

> the sRGB gamut, but it's clamped appropriately when actually fed to

> the device.





> If there's no good algorithm to convert from CIE colorspaces to the

> gamut used by current devices, and no actual devices that display

> colors in the CIE colorspace gamuts, then what's the use of specifying

> colors in a CIE colorspace today?



> ~TJ
Received on Saturday, 18 September 2010 02:01:35 GMT

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