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Re: [css4-color] HLC <= CIE-La*b*

From: Chris Lilley <chris@w3.org>
Date: Tue, 15 Nov 2011 16:19:02 +0100
Message-ID: <1326932691.20111115161902@w3.org>
To: Christoph P├Ąper <christoph.paeper@crissov.de>
CC: W3C Style <www-style@w3.org>, Kevin Bortis <kevin@bortis.ch>
On Tuesday, November 15, 2011, 3:56:58 PM, Christoph wrote:

>> The transformation from CIE-L*C*h to CIE-L*a*b:
>> L = L a = C * cos(h)  b = C * sin(h)
>> L = L C = sqrt(a^2+b^2)       h = arctan(b/a)

>> "RAL Design(TM)". The values printed on the cards are in the format
>> HLC which is a lot easier to use in practice than LCh.

CP> HLC seems fine enough. It is reminiscent of HSL, though,

Actually, the other way round. Historically, CIE Lab and LCHab were standardised in 1976; HSL and HSV were attempts to get the same polar formulation in RGB space (but with attendant problems that L and V are not independent of H, H is not perceptually even, etc). I believe that the original proposal for HSL mentioned explicitly that it was inspired by LCHab.

-- 
 Chris Lilley   Technical Director, Interaction Domain                 
 W3C Graphics Activity Lead, Fonts Activity Lead
 Co-Chair, W3C Hypertext CG
 Member, CSS, WebFonts, SVG Working Groups
Received on Tuesday, 15 November 2011 15:19:06 GMT

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