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From: Cousin Ricky
Subject: What clipka actually said about the srgb keywords
Date: 14 Aug 2023 14:09:13
Message: <64da6dc9$1@news.povray.org>
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I just ran across these comments while looking for something else.
Clipka's initial warning was:
https://news.povray.org/58625d1f%241%40news.povray.org
His correction to the initial warning:
https://news.povray.org/5862ea88%241%40news.povray.org
To summarize the two posts:
... you need to use
#declare C = srgb <R,G,B>;
colour C * Brightness
rather than
colour srgb <R,G,B>*Brightness
because the latter would be interpreted as
colour srgb (<R,G,B>*Brightness)
My response was:
The moral seems to be get all of your srgb declarations out of the way
as early as possible--including before you do any math on such colors.
This is in agreement with what Ive and I said in Kenneth's thread two
years ago, less the note about byte triplets. I can see how confusion
could arise about dividing by 255, but that situation is different.
Post a reply to this message
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Cousin Ricky <ric### [at] yahoo com> wrote:
> I just ran across these comments while looking for something else.
> Clipka's initial warning was:
> https://news.povray.org/58625d1f%241%40news.povray.org
>
> His correction to the initial warning:
> https://news.povray.org/5862ea88%241%40news.povray.org
>
> To summarize the two posts:
>
> ... you need to use
>
> #declare C = srgb <R,G,B>;
> colour C * Brightness
>
> rather than
>
> colour srgb <R,G,B>*Brightness
>
> because the latter would be interpreted as
>
> colour srgb (<R,G,B>*Brightness)
> [...]
This clears up an issue I had a few days ago: multiplying an srgb value at
declaration gave me much different results than when multiplying it within a
sky_sphere's color map. Very good to know, thanks!
Sam
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From: Thomas de Groot
Subject: Re: What clipka actually said about the srgb keywords
Date: 15 Aug 2023 02:20:13
Message: <64db191d$1@news.povray.org>
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Op 14/08/2023 om 20:09 schreef Cousin Ricky:
> I just ran across these comments while looking for something else.
> Clipka's initial warning was:
> https://news.povray.org/58625d1f%241%40news.povray.org
>
> His correction to the initial warning:
> https://news.povray.org/5862ea88%241%40news.povray.org
>
> To summarize the two posts:
>
> ... you need to use
>
> #declare C = srgb <R,G,B>;
> colour C * Brightness
>
> rather than
>
> colour srgb <R,G,B>*Brightness
>
> because the latter would be interpreted as
>
> colour srgb (<R,G,B>*Brightness)
>
> My response was:
> The moral seems to be get all of your srgb declarations out of the way
> as early as possible--including before you do any math on such colors.
>
> This is in agreement with what Ive and I said in Kenneth's thread two
> years ago, less the note about byte triplets. I can see how confusion
> could arise about dividing by 255, but that situation is different.
Thank you indeed! I have had a lot of confusion about this issue in the
(recent) past as you may remember :-] . This seems to clearly summarize
the problem.
--
Thomas
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