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Re: [css3-images] Proposed Gradients changes

From: Alan Gresley <alan@css-class.com>
Date: Tue, 30 Nov 2010 02:04:40 +1100
Message-ID: <4CF3C108.1010905@css-class.com>
To: Chris Lilley <chris@w3.org>
CC: "Tab Atkins Jr." <jackalmage@gmail.com>, Anne van Kesteren <annevk@opera.com>, Brad Kemper <brad.kemper@gmail.com>, www-style list <www-style@w3.org>
On 25/11/2010 5:13 PM, Chris Lilley wrote:
> On Thursday, November 25, 2010, 4:56:03 AM, Alan wrote:
[snip]
> http://www.w3.org/TR/css3-color/#rgb-color
>
>
>>> If the sRGB value (-20,270,250) falls within the device gamult
>>> it will be displayed, otherwise it will be clipped so that it
>>> falls inside the device gamut.
>
>
> AG>  So why doesn't CSS3 color say this?
>
> It does. Same section:
>
> "Values outside the device gamut should be clipped or mapped into the
> gamut when the gamut is known: the red, green, and blue values must
> be changed to fall within the range supported by the device"

CSS3 color does not say what is displayed for values outside the device 
gamut. Also the example of what is outside a sRGB gamut in the spec is a 
printer. A printer uses CMYK colours which is the opposite of Adobe RGB 
color space which is RGBW.

> AG>  The way the spec is written, there AG>  is nothing that
> indicates that author can use deep color like scRGB.
>
> Ah. Not the same thing.
>
> In CSS3 color, all colours are specified in sRGB colour space and
> output devices (monitors, printers) can have other gamuts. Some
> colours in sRGB may be outside device gamut, and some colours outside
> sRGB may inside device gamut.

Yes, I aware of this. We can also include image capturing devices like a 
digital camera.

> If you want to directly specify colours in another colourspace, CSS3
> colour won't help. Other specifications will define that.

CSS4 Color?

> AG>  Also, this doesn't answer my initial question regarding
> gradients.
>
> AG>  At what point does the below gradient use imaginary colors of
> the scRGB AG>  gamut?
>
> AG>  background: linear-gradient(left, rgba(-20, 270, 250),
> transparent);
>
> AG>  If a gradient was premultiplied at some point it could be using
> AG>  imaginary colors.
>
> I don't follow how you infer that.

See below.

> AG>  If a gradient was un-premultiplied it may use real AG>  color
> along it whole gradient.
>
> AG>  I can not answer this myself since there is no CIE colorspace
> that maps AG>  color to a x, y and z matrix
>
> Not sure what you mean by that (and I suspect you mean X Y Z, or
> possibly x y Y, but not x y z).

I talking about x, y, z matrix which uses Cartesian coordinates in three 
dimensions [1] or Geometric representation [2]. CIE 1931 x,y 
chromaticity space is is not sRGB colorspace. the former is shaped like 
a convex horseshoe and the later is a cubed prism with x, y, z coordinates.

What I am asking is if there is actual color at all points between the 
rings of monochromatic colors and the line of purples and the top of the 
x, y, z prism which is white. Please view what I trying to express in 
mere words.

<http://css-class.com/images/xyz-colorspace.png>

If a gradient was premultiplied, then any color within  the x, y, z 
prism goes *directly* from that point of color to the point at the top 
of the x, y, z prism. Appearing over a white background, a yellow to 
transparent gradient is mixed like pigments.

To base a spec for gradient on the mixing of colour like pigments is 
like testing gradients of color to transparent just with a white even 
background and being amazed that the midpoint between yellow and 
transparent is a pale olive but them believing that it is gray. This is 
not a paint class.

  > AG>  imaginary colors.
>
> AG>  and I'm am ignorant if any browser can show AG>  scRGB color. I
> will just have to search my house for my HDMI cable AG>  instead of
> VGA cable.
>
> You also need OS support, and video card and driver support for
> greater than 8 bits per component. There is no point using wide-gamut
> displays if you are limited to 8 bits per component.

I have Window7 with a 64-bit OS with a NVIDIA Geforce GT 330 graphic 
card. I even have IE9 for 64-bit. I believe that my DVI cable should do 
the job. No need for HDMI.

> Windows 7 has some support
> http://news.softpedia.com/news/Windows-7-High-Color-Support-98741.shtml
>
>  and IE9 has some colour management support, so I would try there
> first. Maybe someone on the IE9 team could comment on whether IE9
> hooks into the Win7 high colour support.

Well that would be helpful. Some feedback from an organization that 
supposedly supports scRGB colorspace.



1. 
<http://en.wikipedia.org/wiki/Cartesian_coordinate_system#Cartesian_coordinates_in_three_dimensions>
2. <http://en.wikipedia.org/wiki/RGB_color_model#Geometric_representation>
-- 
Alan http://css-class.com/

Armies Cannot Stop An Idea Whose Time Has Come. - Victor Hugo
Received on Monday, 29 November 2010 15:05:20 GMT

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