Re: [css4-color] Grayscale shorthand (with alpha)

On Wednesday, April 18, 2012, 5:05:14 PM, Tab wrote:

TAJ> On Wed, Apr 18, 2012 at 5:03 AM, Chris Lilley <chris@w3.org> wrote:
>> On Tuesday, April 17, 2012, 11:01:17 AM, Rudolph wrote:

>> RG> I find myself writing things like rgba(0, 0, 0, .5) or rgba(192, 192,
>> RG> 192, .8) dozens of times a day, mostly for shadows. It's always some
>> RG> shade of gray with some alpha value.

>> RG> Do you think there's room for a grayscale color shorthand?

>> What properties would you want it to have? For example, would 50% gray correspond to a color which is visually 50% between black and white?

>> The CIE lightness (L*) has that property. L=0 is black, L=100 is the media white. L=50 is exactly a mid grey.

>> It could be used by itself or as part of the CIE Lab or LCH color spaces (C and H are chroma and hue angle) - to give warm or cool greys for example.

TAJ> I'm definitely interested in investigating the CIELab/LCH color spaces
TAJ> at some point, 

What do you want to know about them? 

(Rudolph, note by the way that LCH is not the same as HSV or HSL)

TAJ> and we could potentially hook gray() up to that instead
TAJ> of RGB.  I wouldn't want to make a choice yet.

Yes, it really depends on what the requirements are.

Whatever we decide on has to have a defined colorimetric interpretation, though (so defining it as L*, or alternatively as the neutral axis of sRGB, would work; defining it as "your mileage may vary" device gray would not).

-- 
 Chris Lilley   Technical Director, Interaction Domain                 
 W3C Graphics Activity Lead, Fonts Activity Lead
 Co-Chair, W3C Hypertext CG
 Member, CSS, WebFonts, SVG Working Groups