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<p>(I don't seem to have got the message from Alexei, just the reply
to it)<br>
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<div class="moz-cite-prefix">On 2023-07-19 23:08, Hin-Tak Leung
wrote:<br>
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<div><span style="color: rgb(38, 40, 42); font-size: 13px;">On
Wednesday, 19 July 2023 at 15:27:20 BST, Podtelezhnikov
<a class="moz-txt-link-rfc2396E" href="mailto:apodtele@gmail.com"><apodtele@gmail.com></a> wrote:</span><br>
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<div>> Hin-Tak,<br clear="none">
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This is probably both a spec question & a
technical question. What is the recommendation
for COLRv1 when the rendering target media is
not capable of color?</div>
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<div>> Are you asking about RGB to gray conversion?
There are multiple specs with slightly different
formulas and barely noticeable differences, with and
without gamma correction. I’m is all pretty
arbitrary without settled consensus. <br>
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<p>Pardon my French but that is utter hogwash. "without settled
consensus" indeed!<br>
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<p>The palette colors are explicitly in the sRGB colorspace, and
thus their conversion to luminance is precisely and unambiguously
defined. First undo gamma encoding, then take the weighted sum.
See<br>
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<a class="moz-txt-link-freetext" href="https://drafts.csswg.org/css-color-4/#predefined-sRGB">https://drafts.csswg.org/css-color-4/#predefined-sRGB</a></p>
<p>and</p>
<p><a class="moz-txt-link-freetext" href="https://drafts.csswg.org/css-color-4/#color-conversion-code">https://drafts.csswg.org/css-color-4/#color-conversion-code</a><br>
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<div>> Gray = 0.3R + 0.6G + 0.1B</div>
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<div>> is good enough.</div>
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Large errors, mostly from ignoring the effects of gamma encoding.
You seem to be vaguely remembering the equation for the NTSC
colorspace. Please do not spread this sort of easily disprovable,
wildly incorrect misinformation.<br>
<p>For sRGB, once transformed to linear-light, the factors are
actually</p>
<p>0.21263900587151027 R + 0.715168678767756 G + 0.07219231536073371
B<br>
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<pre class="moz-signature" cols="72">--
Chris Lilley
@svgeesus
Technical Director @ W3C
W3C Strategy Team, Core Web Design
W3C Architecture & Technology Team, Core Web & Media</pre>
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