clipka <ano### [at] anonymousorg> wrote:
> Am 22.12.2016 um 05:08 schrieb Dave Blandston:
> > clipka <ano### [at] anonymousorg> wrote:
> >> The second image shows essentially the same scene with `assumed_gamma
> >> 2.2`, with the diffuse settings (`diffuse` and `brilliance`) adjusted to
> >> get exactly the same diffuse effect out of the different colour math.
> >
> > Please forgive my ignorance, but does that mean the default settings for diffuse
> > and brilliance are meant to give the most visually appealing results with an
> > assumed_gamma of 2.2?
>
> It is more complicated than that.
>
> > I never really gave assumed_gamma much thought. I just noticed that setting it
> > to 1.0 produced a washed-out result so I picked 2.2 and never thought about it
> > again.
>
> Here are a few facts:
>
> - The brilliance default of 1 fits /perfectly/ with `assumed_gamma 1.0`,
> because the developers back then naively implemented a formula that was
> designed for linear colours. The whole `brilliance` mechanism is an
> awfully hackish thing, and it so happens that it can be used to achieve
> the same proper look with other gamma settings (as far as diffuse goes),
> so my guess is that it was introduced specifically for the purpose of
> fixing the look of diffuse objects, in times when people probably didn't
> even know what gamma handling was.
>
> - The diffuse default of 0.7 was presumably introduced in times when bad
> gamma handling was the norm, and it can be assumed that it was set in
> such a way as to get pleasing results in /that/ environment. In a gamma
> 1.0 scenario, that would correspond to a setting of about 0.45.
>
>
> - As Warp demonstrated not long ago, one main reason (besides trying to
> use gamma-pre-corrected colours without the "srgb" keyword) for the
> washed-out look in gamma 1.0 mode seems to be the "ambient" default:
> That setting, too, was quite certainly designed for a gamma of about
> 2.2, and in a gamma 1.0 scenario that would correspond to an ambient
> setting of 0.006 (though that number is difficult to nail down, as
> ambient is always added to colours, and adding colours without proper
> gamma handling greatly distorts them, particularly if their absolute
> value is rather small.)
>
>
> - Without proper gamma handling, there is stuff that you just simply
> /cannot/ get right simultaneously (as demontrated with these images); so
> you may need a /lot/ of tweaking to get /somewhat/ close to a realistic
> look, and you'll have to do this /over and over again/ for virtually
> each and every scene, as you'll need to fine-tune yor materials for the
> given lighting conditions and vice versa. On the other hand, with gamma
> 1.0 all it takes is some experience, and once you get your materials
> right you can re-use them quite easily in virtually every lighting
> condition. (Also, with proper gamma handling the number of knobs to
> tweak is smaller, since you never need to fiddle with any of those
> unrealistic hacks like brilliance, reflection exponent, or light source
> fade_power values other than 2.0.)

Interesting. Do the default values now reflect assumed gamma 1.0 then or do we
still have to tweak them for assumed gamma 1.0?

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> clipka <ano### [at] anonymousorg> wrote:
>> Am 22.12.2016 um 05:08 schrieb Dave Blandston:
>>> clipka <ano### [at] anonymousorg> wrote:
>>>> The second image shows essentially the same scene with `assumed_gamma
>>>> 2.2`, with the diffuse settings (`diffuse` and `brilliance`) adjusted to
>>>> get exactly the same diffuse effect out of the different colour math.
>>>
>>> Please forgive my ignorance, but does that mean the default settings for diffuse
>>> and brilliance are meant to give the most visually appealing results with an
>>> assumed_gamma of 2.2?
>>
>> It is more complicated than that.
>>
>>> I never really gave assumed_gamma much thought. I just noticed that setting it
>>> to 1.0 produced a washed-out result so I picked 2.2 and never thought about it
>>> again.
>>
>> Here are a few facts:
>>
>> - The brilliance default of 1 fits /perfectly/ with `assumed_gamma 1.0`,
>> because the developers back then naively implemented a formula that was
>> designed for linear colours. The whole `brilliance` mechanism is an
>> awfully hackish thing, and it so happens that it can be used to achieve
>> the same proper look with other gamma settings (as far as diffuse goes),
>> so my guess is that it was introduced specifically for the purpose of
>> fixing the look of diffuse objects, in times when people probably didn't
>> even know what gamma handling was.
>>
>> - The diffuse default of 0.7 was presumably introduced in times when bad
>> gamma handling was the norm, and it can be assumed that it was set in
>> such a way as to get pleasing results in /that/ environment. In a gamma
>> 1.0 scenario, that would correspond to a setting of about 0.45.
>>
>>
>> - As Warp demonstrated not long ago, one main reason (besides trying to
>> use gamma-pre-corrected colours without the "srgb" keyword) for the
>> washed-out look in gamma 1.0 mode seems to be the "ambient" default:
>> That setting, too, was quite certainly designed for a gamma of about
>> 2.2, and in a gamma 1.0 scenario that would correspond to an ambient
>> setting of 0.006 (though that number is difficult to nail down, as
>> ambient is always added to colours, and adding colours without proper
>> gamma handling greatly distorts them, particularly if their absolute
>> value is rather small.)
>>
>>
>> - Without proper gamma handling, there is stuff that you just simply
>> /cannot/ get right simultaneously (as demontrated with these images); so
>> you may need a /lot/ of tweaking to get /somewhat/ close to a realistic
>> look, and you'll have to do this /over and over again/ for virtually
>> each and every scene, as you'll need to fine-tune yor materials for the
>> given lighting conditions and vice versa. On the other hand, with gamma
>> 1.0 all it takes is some experience, and once you get your materials
>> right you can re-use them quite easily in virtually every lighting
>> condition. (Also, with proper gamma handling the number of knobs to
>> tweak is smaller, since you never need to fiddle with any of those
>> unrealistic hacks like brilliance, reflection exponent, or light source
>> fade_power values other than 2.0.)
>
> Interesting. Do the default values now reflect assumed gamma 1.0 then or do we
> still have to tweak them for assumed gamma 1.0?
>

The diffuse should be OK, maybe reduce ambient. For the rest, it should 
be correct.

something in that range, in the global_settings block.

It's relatively simple: assumed_gamma 1 = correct calculations and 
minimal tweaking. assumed_gamma <> 1 = incorrect calculations and LOTS 
of tweakings.

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Alain <kua### [at] videotronca> wrote:

> > clipka <ano### [at] anonymousorg> wrote:
> >> Am 22.12.2016 um 05:08 schrieb Dave Blandston:
> >>> clipka <ano### [at] anonymousorg> wrote:
--->8
> >> - The brilliance default of 1 fits /perfectly/ with `assumed_gamma 1.0`
---8<
> >> - The diffuse default of 0.7
--->8  I believe that should be 0.6 for default diffuse. And 0.7 is used as an
example in the docs.
--->8---8<---

> something in that range, in the global_settings block.

Less the "s", ambient_light.
I like finding mistakes.  :)

Bob

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Am 24.12.2016 um 00:02 schrieb Alain:

>> Interesting. Do the default values now reflect assumed gamma 1.0 then
>> or do we
>> still have to tweak them for assumed gamma 1.0?

As I said, the default for `brilliance` does (as does the default for
reflection `exponent`), while the default for `ambient` doesn't.

The default for `diffuse` is in the right ballpark.


> The diffuse should be OK, maybe reduce ambient. For the rest, it should
> be correct.

> something in that range, in the global_settings block.

There's a caveat to this: If you also use other ambient values in your
materials, that change would reduce higher values too much, and reduce
lower values too little.

So you might as well stick to the default of `ambient_light 1.0`, and
instead use:

    default { finish { ambient 0.01 } }

which I think is the cleaner fix.

(Or use radiosity anyway ;))

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On 24-12-2016 6:43, clipka wrote:
> (Or use radiosity anyway ;))
>

/That/ is what I was missing in the discussion above. Except for ambient 
which is switched off with radiosity, any peculiarities to be noted?

-- 
Thomas

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clipka <ano### [at] anonymousorg> wrote:
> Am 24.12.2016 um 00:02 schrieb Alain:
>
> >> Interesting. Do the default values now reflect assumed gamma 1.0 then
> >> or do we
> >> still have to tweak them for assumed gamma 1.0?
>
> As I said, the default for `brilliance` does (as does the default for
> reflection `exponent`), while the default for `ambient` doesn't.
>
> The default for `diffuse` is in the right ballpark.
>
>
> > The diffuse should be OK, maybe reduce ambient. For the rest, it should
> > be correct.

> > something in that range, in the global_settings block.
>
> There's a caveat to this: If you also use other ambient values in your
> materials, that change would reduce higher values too much, and reduce
> lower values too little.
>
> So you might as well stick to the default of `ambient_light 1.0`, and
> instead use:
>
>     default { finish { ambient 0.01 } }
>
> which I think is the cleaner fix.
>
> (Or use radiosity anyway ;))

Just glad you explained all this once again.
I am always going to be tempted to change the way it's supposed to be but that's
from force of habit, wanting to see how a render looks one way then another...
and another...
It's also a good thing to know what does best overall, in general, and go from
there only afterward. If I can relearn how to go about things maybe that's still
possible. :)

Bob

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clipka <ano### [at] anonymousorg> wrote:
> So you might as well stick to the default of `ambient_light 1.0`, and
> instead use:
>
>     default { finish { ambient 0.01 } }

I selected a random scene and changed the gamma setting to 1.0 and added this
default finish, but the rendered scene still had that "washed-out" appearance.
Does this have something to do with the differences between version 3.7 and
3.71? (I'm using version 3.7.)

Regards,
Dave Blandston

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Am 24.12.2016 um 12:53 schrieb Dave Blandston:
> clipka <ano### [at] anonymousorg> wrote:
>> So you might as well stick to the default of `ambient_light 1.0`, and
>> instead use:
>>
>>     default { finish { ambient 0.01 } }
> 
> I selected a random scene and changed the gamma setting to 1.0 and added this
> default finish, but the rendered scene still had that "washed-out" appearance.
> Does this have something to do with the differences between version 3.7 and
> 3.71? (I'm using version 3.7.)

No, there are no differences between 3.7 and 3.7.1 in this respect.

There are many reasons why a legacy scene may /still/ look washed-out:

- The scene might be using explicit `ambient` settings.

- Even though partial blame is now put on `ambient`, it is also still
true that pigment colours specified using `rgb` will /per se/ tend to
look less saturated and brighter in an `assumed_gamma 1.0` scene than in
a legacy scene.

- As demonstrated, non-linear gamma messes up /any/ combination of
multiple finish effects (e.g. diffuse and reflection) in a very
non-linear fashion; consequently, any scene tweaked to look reasonably
good despite these quirks /will/ most certainly look unexpected when
setting `assumed_gamma 1.0`, and will essentially have to be "un-tweaked".

- Another potential factor is that you may simply have gotten accustomed
to the excessive contrast of non-linear scenes over the years, and may
now be expecting more contrast than is realistic. (Reality is rarely
"moody" -- even professional photographers routinely "cheat" on such
scenes, from employing tinted spotlights to choosing a highly non-linear
photographic film to applying tonemapping in a post-processing step.)

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clipka <ano### [at] anonymousorg> wrote:
> - Another potential factor is that you may simply have gotten accustomed
> to the excessive contrast of non-linear scenes over the years, and may
> now be expecting more contrast than is realistic. (Reality is rarely
> "moody" -- even professional photographers routinely "cheat" on such
> scenes, from employing tinted spotlights to choosing a highly non-linear
> photographic film to applying tonemapping in a post-processing step.)

That's probably what has happened. Obviously you have shown that gamma 1.0 is
mathematically correct and that is very important to know. It's hard to resist
the richer, more dramatic colors that gamma 2.2 produces though!

Regards,
Dave Blandston

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Am 24.12.2016 um 22:01 schrieb Dave Blandston:
> clipka <ano### [at] anonymousorg> wrote:
>> - Another potential factor is that you may simply have gotten accustomed
>> to the excessive contrast of non-linear scenes over the years, and may
>> now be expecting more contrast than is realistic. (Reality is rarely
>> "moody" -- even professional photographers routinely "cheat" on such
>> scenes, from employing tinted spotlights to choosing a highly non-linear
>> photographic film to applying tonemapping in a post-processing step.)
> 
> That's probably what has happened. Obviously you have shown that gamma 1.0 is
> mathematically correct and that is very important to know. It's hard to resist
> the richer, more dramatic colors that gamma 2.2 produces though!

It may get easier once tonemapping is officially added to POV-Ray.

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