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Re: [CSS3 Colors] HSL colors, hue and allowed values, [CSS3 gcpm] CMYK colors and allowed values.

From: Brad Kemper <brad.kemper@gmail.com>
Date: Wed, 29 Jul 2009 07:43:02 -0700
Cc: <www-style@w3.org>
Message-Id: <BB4ACF27-DD6A-44FA-A5C8-E87F25572CD4@gmail.com>
To: "Ludger Buenger" <ludger.buenger@realobjects.com>
Traditionally, CMYK values have always been percentages. Whether this  
is represented with a decimal or with a percentage sign doesn't make  
that much difference to me, but using a 256 range would be very  
unusual to designers for that, and would require converting from  
numbers they are used to using when designing for print. I would  
expect both percentage (with a "%") and decimal notation to be  
allowed, just as it is in rgb() and rgba(), even though the GCPM  
doesn't specify.

I don't really have any problem with an optional unit type being used  
for degrees in HSL, except that I don't think many people would  
actually type it, and it seems unnecessary since degrees is the only  
type that can be used there.


On Jul 29, 2009, at 4:30 AM, Ludger Buenger wrote:

> Hi everyone,
>
> We are currently in the process of implementing colors defined in  
> the current working draft of the colors module (and the one color  
> definition from the gcpm module).
>
>
>
> Regarding HSL colors:
>
> According to the working draft (http://www.w3.org/TR/2008/WD-css3-color-20080721/#hsl-color 
> ), HSL colors accept three parameters.
>
>
> The first HSL color parameter represents the hue and accepts numeric  
> values representing an angle and should be interpreted as degrees  
> modulo 360.
>
> Since CSS knows unit types representing angles (deg, rad and grad),  
> I'd like to suggest that if an explicit unit type is set, this one  
> should be used, if no unit type is given it should be interpreted as  
> degrees.
> Current working draft only permits numeric values.
>
> Question: does it make sense to also accept percentage values with  
> 100% equaling 360 degrees?
>
>
> The second and third parameter of an HSL color represent saturation  
> and lightness and are defined to be percentages.
>
> Here we also have questions:
> Does it make sense to accept numeric values if the percent symbol  
> has been omitted and how should they be interpreted?
>
> Since the RGB color definition permits both percentage and numeric  
> values, but numeric values are interpreted as a range from 0 to 255  
> with 255 representing 100%, to me it makes sense to handle this  
> similar in HSL colors.
> But I am not a colors expert, so maybe this is a bad idea.
>
>
>
>
> Regarding CMYK colors (from the current working draft of CSS3 gcpm http://www.w3.org/TR/2007/WD-css3-gcpm-20070504/#cmyk-colors) 
> :
>
> According to the example given in the gcpm working draft, the cmyk  
> color function accepts 4 values being numeric float values in the  
> range 0.0 to 1.0 representing the amount of color to be applied.
>
> Is there a rationale behind this allowed values definition differing  
> from the definition of the allowed values in the rgb color function?
>
> From my point of view, I would expect the allowed values of the cmyk  
> color function to be analogous to the rgb function:
> a percentage value or a value between 0 and 255 with 255  
> representing 100% - for the sole reason of being defined the same  
> way as rgb colors are defined.
>
>
>
> Any comments?
>
>
> Best regards,
>
> Ludger
>
>
> --
> Dipl.-Inf. Ludger Bünger
> Senior Software Engineer
> Product Development
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Received on Wednesday, 29 July 2009 14:43:51 GMT

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