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29 May 2024 03:13:23 EDT (-0400)
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From: clipka
Subject: Re: screen.inc in 3.7 - strange differences in lighting!
Date: 25 Aug 2015 01:26:30
Message: <55dbfc86$1@news.povray.org>
Am 24.08.2015 um 20:19 schrieb "Jörg \"Yadgar\" Bleimann":

> O. k., meanwhile I also found out that srgb does not expect a four-part
> color vector - I removed the fourth value, and now everything works fine
> (see attachment)!

Whoops - it never crossed my mind that the keyword could be
misinterpreted that way, but yes, now that you mention it I see why...


For the records: The "srgb" keyword (along with its siblings, "srgbf",
"srgbt" and "srgbft") was chosen because it tells POV-Ray to interpret
the following vector (or the RGB portion of it, for the sibling
keywords) as colour coordinates in the colour space officially called
"sRGB" ("standard RGB").

This colour space has the benefit of (A) being a good approximation of
Your Average Uncalibrated Computer Display (it was designed in 1996
specifically to match typical display hardware of that time), and (B)
indeed having become a de-facto standard supported by everything that is
even remotely aware of colour spaces - including the World Wide Web,
which officially defaults to sRGB for everything that isn't explicitly
colour managed.


(Also for the records, nitpicking section, POV-Ray only properly
supports sRGB if you presume that its internal colour space uses the
same RGB primaries; that's a valid assumption though, as POV-Ray makes
no claims about its RGB primaries anywhere else, so POV-Ray's claim to
support sRGB can thus be interpreted as an implicit definition of its
internal RGB primaries as being those of sRGB.)


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From: Cousin Ricky
Subject: Re: screen.inc in 3.7 - strange differences in lighting!
Date: 28 Aug 2015 23:22:28
Message: <55e12574@news.povray.org>
On 2015-25-08 01:26 AM (-4), clipka wrote:
> Am 24.08.2015 um 20:19 schrieb "Jörg \"Yadgar\" Bleimann":
>
>> O. k., meanwhile I also found out that srgb does not expect a four-part
>> color vector - I removed the fourth value, and now everything works fine
>> (see attachment)!
>
> Whoops - it never crossed my mind that the keyword could be
> misinterpreted that way, but yes, now that you mention it I see why...

Me neither.  His comment about trying values for "s" went straight by me.


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From: Mike Horvath
Subject: Re: screen.inc in 3.7 - strange differences in lighting!
Date: 1 Sep 2015 21:40:31
Message: <55e6538f$1@news.povray.org>
On 8/21/2015 5:42 PM, "Jörg \"Yadgar\" Bleimann" wrote:
> Hi(gh)!
>
> To add the scrolling info text (to be displayed when the ball runs
> through one of the two rotating "i" characters), I now used screen.inc
> in my POVigma project - and noticed a strange deviation in brightness
> and contrast (lighting settings are not changed since)!
>
> With screen.inc (nevertheless using a conventional camera, as a
> straight-down top view otherwise would yield an error), the whole scene
> is brighter and with less contrast, as showed in the two attached pictures.
>
> How can I fix this?
>
> See you in Khyberspace!
>
> Yadgar

IIRC I encountered some washed out and overly bright colors when 
switching between orthographic and perspective camera modes in 
screen.inc. Compare these two images:

http://s421.photobucket.com/user/SharkD2161/media/Povray/pov_screenupdate_a.png.html
http://s421.photobucket.com/user/SharkD2161/media/Povray/pov_screenupdate_b.png.html


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