POV-Ray : Newsgroups : povray.general : Lightsys IV may not work correctly in POV 3.8 Server Time: 26 Feb 2021 22:02:06 GMT
  Lightsys IV may not work correctly in POV 3.8 (Message 1 to 4 of 4)  
From: Cousin Ricky
Subject: Lightsys IV may not work correctly in POV 3.8
Date: 30 Jan 2021 20:02:37
Message: <6015bb5d@news.povray.org>
See thread "FYI. Watch out for bad color to grey value conversions." in 
povray.unix.

Macro Light_Color_Filtered() in Lightsys IV uses .gray, so scenes using 
this macro are unlikely to have proper lighting under the latest 3.8 
build.  This situation is temporary, until 3.8 is debugged; but in the 
meantime, this workaround should work:

First, add this macro to lightsys.inc:

   #macro Light_DotGray (C)
     (0.297 * C.red + 0.589 * C.green + 0.114 * C.blue)
   #end

Then change the Light_Color() call in macro Light_Color_Filtered() to:

   Light_Color(Lct*Flt,Lm*Light_DotGray(filtered)/Light_DotGray(Lct))

I haven't tested this yet, because I wanted to get the info out quickly, 
but it looks straightforward.  Also, this workaround uses the internal 
POV-Ray grayscale formula, which will keep the old behavior, but was 
coded before gamma handling was seriously examined.  A more accurate 
formula can be found in the p.unix thread, although that formula is 
accurate only for the sRGB/BT.709 color systems (which yours probably is 
anyway).


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From: Thomas de Groot
Subject: Re: Lightsys IV may not work correctly in POV 3.8
Date: 31 Jan 2021 07:20:30
Message: <60165a3e$1@news.povray.org>
Op 30/01/2021 om 21:02 schreef Cousin Ricky:
> See thread "FYI. Watch out for bad color to grey value conversions." in 
> povray.unix.
> 
> Macro Light_Color_Filtered() in Lightsys IV uses .gray, so scenes using 
> this macro are unlikely to have proper lighting under the latest 3.8 
> build.  This situation is temporary, until 3.8 is debugged; but in the 
> meantime, this workaround should work:
> 

Thanks for this. One question: after 3.8 is debugged, do we need to put 
Lightsys IV back to its original values? If yes, it might be worthwhile 
to keep the existing code commented out.

-- 
Thomas


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From: Cousin Ricky
Subject: Re: Lightsys IV may not work correctly in POV 3.8
Date: 31 Jan 2021 15:32:33
Message: <6016cd91$1@news.povray.org>
On 2021-01/31 3:20 AM (-4), Thomas de Groot wrote:
> 
> Thanks for this. One question: after 3.8 is debugged, do we need to put 
> Lightsys IV back to its original values? If yes, it might be worthwhile 
> to keep the existing code commented out.

No, it is not necessary.  In fact, if you're up to the challenge, an 
even better idea would be to utilize the xyY macros in CIE.inc.  But 
keeping the original code commented out is not a bad idea.

I typically rename the original file anyway.


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From: Thomas de Groot
Subject: Re: Lightsys IV may not work correctly in POV 3.8
Date: 1 Feb 2021 07:18:57
Message: <6017ab61$1@news.povray.org>
Op 31/01/2021 om 16:32 schreef Cousin Ricky:
> On 2021-01/31 3:20 AM (-4), Thomas de Groot wrote:
>>
>> Thanks for this. One question: after 3.8 is debugged, do we need to 
>> put Lightsys IV back to its original values? If yes, it might be 
>> worthwhile to keep the existing code commented out.
> 
> No, it is not necessary.  In fact, if you're up to the challenge, an 
> even better idea would be to utilize the xyY macros in CIE.inc.  But 
> keeping the original code commented out is not a bad idea.
> 
> I typically rename the original file anyway.

Very good. I generally do the last too, with a comment in the header.

-- 
Thomas


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