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

From: Lars Borg <borg@adobe.com>
Date: Thu, 7 Sep 2017 01:48:03 +0000
To: David Singer <singer@mac.com>, Peter Occil <poccil14@gmail.com>
CC: "public-colorweb@w3.org" <public-colorweb@w3.org>, "www-style@w3.org" <www-style@w3.org>
Message-ID: <D5D5C82F.19FBB%borg@adobe.com>
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)


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
>> "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
>> 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:
>> >
>> > 

>> >
>> > 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. 

>> >
>Dave Singer

Received on Thursday, 7 September 2017 01:48:34 UTC

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