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

From: Peter Occil <poccil14@gmail.com>
Date: Wed, 6 Sep 2017 21:51:39 -0400
To: Lars Borg <borg@adobe.com>, David Singer <singer@mac.com>
Cc: "public-colorweb@w3.org" <public-colorweb@w3.org>, "www-style@w3.org" <www-style@w3.org>
Message-ID: <66c4b233-d468-b56e-9b99-0a5fc3fedf0e@gmail.com>
The matter on black points was already well clarified to me, so that I 
don't need anyone to respond to the black point issue anymore.

--Peter


On 09/06/2017 09:48 PM, Lars Borg wrote:
> It was and still is common practice to map RGB code value 0 to the
> display’s lowest light output and 255 to the display’s max output.
> This applies to practically all digital encodings (except legal range
> 16-235, but for a very different reason)
> As nothing is infinitely black, lowest light is nominally 0.2 for sRGB.
> An exception is digital cinema, where 0x000 actually means total darkness
> (and isn’t achievable)
>
> Lars
>
> On 9/6/17, 1:50 PM, "David Singer" <singer@mac.com> wrote:
>
>>> On Sep 3, 2017, at 5:11 , Peter Occil <poccil14@gmail.com> wrote:
>>>
>>> Letting the style mailing list know.
>>>
>>> -------- Forwarded Message --------
>>> Subject:	Re: Provenance of "sRGB for ICC profiles" on w3.org
>>> Date:	Sun, 3 Sep 2017 08:05:59 -0400
>>> From:	Peter Occil <poccil14@gmail.com>
>>> To:	public-colorweb@w3.org
>>>
>>> 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)?
>> as I understand it, it’s complicated.
>>
>> by the way, I think black point is usually used to refer to the numerical
>> value that represents black, which was 16 when digitizing analog, which
>> allowed sync pulses  to be encoded (in the ‘superblack’ range).
>>
>> but given a value which notionally represents black, I think that the 0.2
>> value represents the permissible light emission of the display when given
>> a signal which asks for ‘black’ (0 usually, 16 in CCIR 601).  what makes
>> it complicated is that production workflows were/are calibrated such that
>> the displays actually did emit this much light, so that they’d verify the
>> quality under ‘maximal black lightness’ conditions. I am not sure if
>> there is a *requirement* to emit this much light (and technologies since
>> CRTs can emit a lot less light, notably OLEDs). so when given a signal to
>> convert to a regime where black is notionally completely black, should
>> you assume this much light emission for the notionally black areas in the
>> input, or not?
>>
>> CRTs are, well, hard to find these days…
>>
>> hope this helps, sorry if it’s off topic
>>
>>
>>>
>>> On 09/02/2017 03:28 PM, Peter Occil wrote:
>>>> I'm aware of the following document posted on the W3C Web site:
>>>>
>>>>
>>> https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.w3.o
>>> rg%2FGraphics%2FColor%2Fsrgb&data=02%7C01%7C%7Cd533a771af7b4636ee8d08d4f5
>>> 822fb2%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C636403386901375692&sd
>>> ata=WE32VqXnoGauCuKDFHGv33JIFUeWn0dcLpoCWzDJX%2BA%3D&reserved=0
>>>
>>>> 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://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.w3
>>> .org%2FArchives%2FPublic%2Fwww-style%2F2016Sep%2F0061.html&data=02%7C01%7
>>> C%7Cd533a771af7b4636ee8d08d4f5822fb2%7Cfa7b1b5a7b34438794aed2c178decee1%7
>>> C0%7C0%7C636403386901375692&sdata=pFNsnITggYSSQCMU3CXXw11UioHv1a9Ot5Cd3Ty
>>> ebPc%3D&reserved=0
>>>
>>>
>> Dave Singer
>>
>> singer@mac.com
>>
>>
Received on Thursday, 7 September 2017 01:52:17 UTC

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