clipka <ano### [at] anonymousorg> wrote:

>
> BTW, the swatch-based assessment has some more limitations than just the
> zoom/interpolation issue:
[snip]
> - It naively presumes the display subsystem's native transfer function
> to match the form f(x) = x^gamma. For display subsystems calibrated to
> e.g. the sRGB, ITU-R BT.709 or ITU-R BT.2020 standards this is
> specifically not the case (for the modern ITU-R BT.2100 standard, aka
> HDR TV, it is probably not even close), and you'll get a gamma value
> that is only valid for 50% physical brightness.

*That's* interesting-- because, after all of this info, I'm *still* having
trouble getting my new monitor to look really accurate! (Not due to any problems
with POV-Ray's gamma set-up tests).  My monitor is a consumer-level VIZIO, a
so-called 'LED' type (which seems to mean only that the 'edge lighting' is from
LEDs-- otherwise, it's an LCD monitor.) It has only typical 'consumer-friendly'
controls-- brightness, color, contrast, tint.. and 'backlight', which looks to
simply brighten or dim the entire image. Otherwise, nothing fancy. Trouble is,
if I set it for a correct gamma of 2.2-- as best I can-- then the overall screen
appearance just doesn't look decent (tonal values and colors.) Depending on the
particular digital-photo image I view on the web, any *slight* off-kilter color
cast is accentuated.  Quite frustrating!

Gamma adjustment is a 'non-linear' thing, of course; but my  monitor seems to
have a NON-LINEAR non-linear response(!)-- at least regarding color intensities.
Green looks a bit too intense... but decreasing the 'green' amount only makes
images look worse.  I do know that our eyes are 'attuned' to seeing shades of
green better than other colors...but something just doesn't look right.  The
monitor also shows BIG visual differences re: the vertical viewing angle. (The
POV-Ray gamma chart's horizontal lines are an 'acid test' for this particular
problem.) And those black/white lines have a slight yellowish color-cast (when
'eye-blurred')-- i.e., not true gray.

Windows 7's built-in 'monitor calibration' feature seems to be quite useless,
BTW. The example *image* there for setting contrast is a guy in a white wrinkled
shirt, along with a black "X" seen against a black(er) background. But it's so
prone to an 'opinion' of correctness that it stinks. But I used it anyway.

Then, returning to POV-ray's older gamma set-up chart at "3.2.3.2 Setting your
Display Gamma", the monitor gamma actually looks decent... more or less. I'm
surprised!

In the newer docs section "2.3.4.1 Setting Up Your Display", with the colored
spheres, the main example image there looks correct as well, gamma-wise, as seen
within the documentation. So far, so good! At this point, my monitor is at the
best settings I can manage to get :-/  (And yes, it's set to its native
resolution -- 1920 X 1080)

As a final test,  I rendered the 'gamma_showcase' file, at both of its
recommended command-line settings. The docs say, "At 100% zoom, both images
should look identical in your viewing software." Is that true?? I ask because
the two PNG images look *radically* different from each other, in all of my
viewing apps including Windows' own image viewer...

.....EXCEPT in Ive's IC/Lilysoft app! There, they both look identical... which is
quite interesting, regarding our previous discussions about PNG gamma and
viewing apps ;-)  And it raises an obvious question, concerning either the
documentation OR the method of how that sphere-test was created:  Is IC the
'target app' for viewing the rendered images? If so, that leaves out lots of
other 'typical' image-viewer apps-- possibly an unintended consequence of the
test scene. As gamma is an important issue, the documentaion needs to mention
this (or the test scene itself needs reworking somehow, to be more inline with
the majority of 'wrong-PNG-gamma' viewing apps??)

Hmm, this smells like a conundrum  :-0

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