Kenneth, thanks for stirring this up again (seriously).  The previous
discussion about this died early.  In case you're feeling patronised
by the other responses, I did read your entire post and I understand
your argument.  I used to agree with you, but now I'm going to try to
convince you to change your ways.

First, two points that are away from your topic.  Thanks for the link
to Norman Koren's test images.  They are the best I have seen and they
allowed me to tweak my apparent gamma down to 2.2.

Second, your test scene demonstrates our eyes' edge-enhancement very
well: the right sides of the 50% bands appear much darker than the
left.  I had to run a colour picker over them to make sure I *was*
seeing things.

Regarding gamma abuse: I feel your pain.  Until this year I did not
have assumed_gamma in my scenes, which led to the behaviour you're
choosing.  I started the scenes before POV (DKB) knew of it.
pigment{Orange} looked orange, shadows looked good, gray10 was very
dark, and my happy little universe was properly lit.

Before we go further you should take a mathematical look at what POV
does to a 0.5 pixel.  It will save you making more test scenes and
examining them in PS.  As pointed out elsewhere in this thread,
section 3.3.3.3 tells what you need to know: with assumed_gamma
omitted or set to display_gamma, your output pixel will be exactly as
set in the pigment.  With display_gamma/assumed_gamma at 2.0, every
pixel value is raised to the power of 1/2.0.  0.5 grey will be raised
above 0.70.

Worse, 0.05 grey is taken to 0.22, which is why the difference between
the darkest two bands in your test seems ridiculous.  To get a
near-black in my scenes that will react to diffuse light but still
look dark, I have to play with input values around 0.03.  I see your
point: it seems daft.  It's just the way it is.

You have illustrated a mind-set very well.  You expect 50% to look
half way between black and white.  I felt the same way about orange.
I felt it shouldn't be yellow.  But that was naivete:  I know now that
trusting the names in colors.inc is foolishness.  I don't think you're
misunderstanding anything, and you certainly didn't deserve to be
spoken down to.  As someone who has recently taken the blue pill, been
assimilated, clicked Start, I feel qualified to respond.

Here is a summary of a summary I have put in a blog entry, which I
won't link here because it is below this NG's audience and will only
draw lofty criticism.  Tek begged us to use {assumed_gamma 1}
elsewhere in these groups after spending a chunk of his life learning
the lesson, and I will do the same:

- Set your assumed_gamma to 1.0.  It will save you pain when you move
  to 3.7.

- Grapple all your colour values down so the fully-lit pigments look
  right again.  Squaring them does the trick.  Try out your colour
  picker: your fully-lit pixels will be as they were with
  assumed_gamma 2.

- That left my half-lit faces too bright, so I reduced their roughness
  and phong_size.  I've switched to the first person here because YMMV.

Leave your display_gamma at 2.0.  Then, if you send us a PNG, our
systems will brighten it slightly so that our displays, which darken
images more than yours does, show us exactly what you see.

Sorry if this sounds preachy but, basically, deep down we're all
trying to save you pain.  Well no, USENET posters being like 4WD
drivers, some of us are showing off, making up for small tackle
(that's a different blue pill, by the way), and taking advantage of
anonymity to behave in ways that would see us beaten to a geeky white
pulp if we tried it at the pub.

But perhaps there is something worthwhile in it.

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