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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