When Thomas de Groot challenged Alain and me to write improved
metals.inc, one of my first thoughts was "Why bother? It's a lost
cause."  Alain's solution was to just replace all the ambients with 0,
but I think that's too simplistic.  That file and golds.inc were written
before POV-Ray had metallic reflection.  File golds.inc goes through an
elaborate ritual to compensate for this deficiency, while metals.inc
ignores the problem completely.  Everything about those two files
screams "OBSOLETE!"  But the challenge still gnaws at me.

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.

Both images use assumed_gamma 1, and the spheres use this finish:

  finish
  { ambient 0 diffuse 0
    reflection { 1 metallic }
    specular albedo 1 metallic
    roughness 1 / 3000
  }

Of course, any improvements to these files will cause old scenes to look
different.  Better, but different.

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