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Re: Your comments on WCAG 2.0 Last Call Draft of April 2006

From: Chris Lilley <chris@w3.org>
Date: Fri, 18 May 2007 03:01:28 +0200
Message-ID: <376004687.20070518030128@w3.org>
To: "Loretta Guarino Reid" <lorettaguarino@google.com>
Cc: public-comments-WCAG20@w3.org

On Friday, May 18, 2007, 1:28:55 AM, Loretta wrote:

LGR> Dear Chris Lilley ,


LGR> PLEASE REVIEW the decisions  for the following comments and reply to
LGR> us by 7 June at public-comments-WCAG20@w3.org to say whether you are
LGR> satisfied with the decision taken. Note that this list is publicly
LGR> archived.

I am fully satisfied by your responses to both of my comments. Thank you for making hose changes.


LGR> ----------------------------------------------------------
LGR> Comment 1:

LGR> Source: http://www.w3.org/mid/20060522154433.CF78166363@dolph.w3.org
LGR> (Issue ID: LC-580)

LGR> Part of Item:
LGR> Comment Type: TE
LGR> Comment (including rationale for proposed change):

LGR> The term "luminosity" is incorrect here (it applies only to certain
LGR> Broadcast video signals). Relative luninance is the correct term. When
LGR> used as a ratio, the difference between absolute and relative
LGR> Luminance can be dropped, but the term luminance rather than
LGR> luminosity should be used.

LGR> http://www.w3.org/TR/2006/WD-WCAG20-20060427/appendixA.html#luminosity-contrastdef
LGR> defines the coefficients for calculating luminance, and its good to
LGR> see that the Rec.709 chromaticities are used (rather than, for
LGR> example, the NTSC ones which do not apply to modern computer monitors
LGR> at all). (the coeeficients are correct, see the "luminanceToAlpha"
LGR> section of http://www.w3.org/TR/SVG11/filters.html#feColorMatrix but
LGR> the specification does not explain why this is so.

LGR> However the text as it stands implies that the formula given is
LGR> universally applicable. it is not. This is particularly importnt when
LGR> printing Web materials.

LGR> Proposed Change:

LGR> change "luminosity" to luminance throughout.

LGR> change "The luminosity of a color is defined as" to "the luminance of
LGR> an sRGB color is defined as".

LGR> change "blue RGB values" to "blue sRGB values" (the equation does not
LGR> apply to other color spaces).

LGR> Remove the exponentiation operator and the 2.2 gamma approximation.
LGR> Instead, use the correct sRGB transfer curve.

LGR> Reference the sRGB specification. See the SVG 1.2Tiny specification
LGR> for an example of how to reference it.

LGR> You may want to note that the equation given is only correct for
LGR> typicalcolor vision (the ISO standard observer). For atypical color
LGR> vision, often incorrectly termed color blindness, different equations
LGR> apply depending on the type of  atypical color vision and the degree
LGR> of severity.
LGR> For more information, please see
LGR> http://www.w3.org/Graphics/atypical-color-response

LGR> ----------------------------
LGR> Response from Working Group:
LGR> ----------------------------

LGR> Thanks for the comments and suggestions.  To take them each in turn:

LGR> CL: change "luminosity" to luminance throughout.
LGR> Since Web content doesn't provide any light output (HTML doesn't give
LGR> off photons) we can't use the word "luminance" (which means light
LGR> output).  However 'relative luminance' is used in the literature for
LGR> the concept we are describing and we are now using this.

Okay.

LGR> CL: change "The luminosity of a color is defined as" to "the luminance
LGR> of an sRGB color is defined as".

LGR> See above regarding luminance. And, we have switched to specifying
LGR> that we are talking about sRGB in our equations.

Good.

LGR> CL: change "blue RGB values" to "blue sRGB values" (the equation does
LGR> not apply to other color spaces).

LGR> Correct and we have done so.

LGR> CL: Remove the exponentiation operator and the 2.2 gamma
LGR> approximation. Instead, use the correct sRGB transfer curve.

LGR> Done.  Now uses the equations from the W3C document on sRGB.

Thanks.

LGR> CL: Reference the sRGB specification. See the SVG 1.2Tiny
LGR> specification for an example of how to reference it.

LGR> Done

LGR> CL: You may want to note that the equation given is only correct for
LGR> typical color vision (the ISO standard observer). For atypical color
LGR> vision, often incorrectly termed color blindness, different equations
LGR> apply depending on the type of atypical color vision and the degree of
LGR> severity. For more information, please see
LGR> http://www.w3.org/Graphics/atypical-color-response.

LGR> We have explained this briefly in our "Understanding" document. A
LGR> longer exposition of this will be released in a paper (since it is too
LGR> complicated to put into How to Meet SC 1.4.3 itself.

Agreed.

LGR>  The contrast
LGR> ratios were set higher than normal and in a way to account for low
LGR> vision and  atypical color vision.

LGR> The paper "Atypical colour response" has also been added as a resource.

Thank you!

LGR> You can find the updated SC and definitions at
LGR> http://www.w3.org/TR/2007/WD-WCAG20-20070517/#visual-audio-contrast-contrast
LGR> and
LGR> http://www.w3.org/TR/2007/WD-WCAG20-20070517/#visual-audio-contrast7
LGR> .

LGR> The Understanding SC 1.4.3 and 1.4.5 documents can be found at
LGR> http://www.w3.org/TR/2007/WD-UNDERSTANDING-WCAG20-20070517/#visual-audio-contrast-contrast
LGR> and
LGR> http://www.w3.org/TR/2007/WD-UNDERSTANDING-WCAG20-20070517/#visual-audio-contrast7
LGR> .

LGR> ----------------------------------------------------------
LGR> Comment 2:

LGR> Source:
LGR> http://www.w3.org/mid/20060522155848.9BF2ADAE7D@w3c4-bis.w3.org
LGR> (Issue ID: LC-581)

LGR> Part of Item:
LGR> Comment Type: TE
LGR> Comment (including rationale for proposed change):

LGR> "3.2.2  Changing the setting of any form control or field does not
LGR> automatically cause a change of context (beyond moving to the next
LGR> field in tab order), unless the authored unit contains instructions
LGR> before the control that describe the behavior"

LGR> Consider a user interface for a map, where form fields such as panning
LGR> controls, layer selections or search boxes are used to zoom,pan, or
LGR> alter a map. This common use seems to be precluded by the text above.

LGR> Proposed Change:

LGR> I regret not being able to suggest suitable text at this time. I can
LGR> see the benefit of what you are trying to do, and I can see that it
LGR> makes non-confomant some interfaces that are currently used. I think
LGR> the text needs to be more precise, and look forward to discussing this
LGR> further with you.

LGR> ----------------------------
LGR> Response from Working Group:
LGR> ----------------------------

LGR> User interfaces that allow the user to select different views of the
LGR> same data cause changes in content, but not changes in context.

Ah, okay.

LGR> Success Criterion 4.1.2 has been changed to require that user agents
LGR> and assistive technology be notified of the changes in state produced
LGR> by such changes in views.

That works for me.


-- 
 Chris Lilley                    mailto:chris@w3.org
 Interaction Domain Leader
 Co-Chair, W3C SVG Working Group
 W3C Graphics Activity Lead
 Co-Chair, W3C Hypertext CG
Received on Friday, 18 May 2007 01:02:03 UTC

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