On 2022-02-22 09:36 (-4), Cousin Ricky wrote:
> 
> One question that must be answered is should we assume that the colors
> are gamma pre-encoded?  Image stock_metal_gamma-srgb.jpg assumes that
> they are, and uses the srgbft keyword to decode them.  Image
> stock_metal_gamma-linear.jpg assumes they are not, and just uses the
> colors as-is.  Comparing them, it seems to me that the colors were not
> pre-encoded, unlike those in colors.inc.

I discovered that the demo scenes from POV-Ray 3.0 explicitly set
assumed_gamma to 2.2, suggesting that the pigment colors were gamma
pre-encoded.  However, as the first OP image shows, this results in
metals that are too dark when used with a realistic finish.  It appears
that the old finishes exaggerated the luminances of the colors while
reducing their saturations, so it seems best to leave the colors as-is,
as if they were not pre-encoded.

Not gamma-decoding the colors does result in hue drift, but I think the
drift is in a better direction.

The attached images show the old finishes without and with radiosity.
Since they were rendered with POV-Ray 3.7, the ambients were
automatically suppressed for the radiosity renders.  The radiosity image
shows that the ambients were not the only problem with the old finishes;
the reflection { metallic } introduced in POV-Ray 3.5 really makes a
difference.

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