Re: Provenance of "sRGB for ICC profiles" on w3.org

That is actually only the case once XYZ is "normalized", so that Y = 0 
is the (sRGB) black point and Y = 1 is the white point.

However, the document I previously linked to (which is actually from the 
ICC and at ref. 1), at section A.6, suggests that XYZ values are 
normalized taking into account the veiling glare luminance ("black 
point" luminance) (in addition to the white point luminance), rather 
than taking into account just the white point luminance, which I 
presumed was the case until now.  (Note that each of the two 
normalizations will result in a different meaning for Y = 0.) Hence my 
question on what luminance (either 0 or 0.2 cd/m^2) sRGB's "black point" is.

Ref. 1. http://www.color.org/chardata/rgb/sRGB.pdf


On 09/03/2017 01:00 PM, Pierre-Anthony Lemieux wrote:
>>   Is it true that the "sRGB black point" (what sRGB defines as black) has a luminance of 0.2 cd/m^2 (absolute Y = 0.2)
>> rather than 0 cd/m^2 (absolute Y = 0, the start of the absolute XYZ scale)?
> ISO 61966-2-1 [1] specifies that [X Y Z] = [0 0 0] yields  [R G B] =
> [0 0 0] (see equation 8).
>
> Furthermore, quantized 8-bit R8 = 255 R' , where R' is non-linear R,
> (see equation 4)
>
> and R' = 12.92 R when R' < 0.04045. (see equation 5)
>
> ... so R8 = 0 when [X Y Z] = [0 0 0] , with the same reasoning
> applying to G8 and B8.
>
> Let me know if I got this wrong.
>
> Best,
>
> -- Pierre
>
> [1] https://webstore.iec.ch/publication/6169
>
> On Sun, Sep 3, 2017 at 5:05 AM, Peter Occil <poccil14@gmail.com> wrote:
>> While I'm at it, that document contains a very questionable statement about
>> the "black point" of sRGB, suggesting that the "black point" has a "veiling
>> glare luminance" of 0.2 cd/m^2 (and indeed that suggestion appears further
>> in some of the formulas in that document).  Is it true that the "sRGB black
>> point" (what sRGB defines as black) has a luminance of 0.2 cd/m^2 (absolute
>> Y = 0.2) rather than 0 cd/m^2 (absolute Y = 0, the start of the absolute XYZ
>> scale)?
>>
>>
>>
>> On 09/02/2017 03:28 PM, Peter Occil wrote:
>>> I'm aware of the following document posted on the W3C Web site:
>>>
>>> https://www.w3.org/Graphics/Color/srgb
>>>
>>> I find it very useful as a reference, but: Where did this document come
>>> from?  Who were its authors?  When was it posted?  I couldn't find it linked
>>> anywhere on the W3C site except on a mailing list message (ref. 1).
>>>
>>> Ref. 1. https://lists.w3.org/Archives/Public/www-style/2016Sep/0061.html
>>>
>>

Received on Sunday, 3 September 2017 18:18:43 UTC