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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)

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 01:48:34 UTC

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