I'm testing out 3.8.0-beta.2 and trying out a scene ported from 3.6. Now it's
complaining "Suspiciously high 'ambient' value found." on textures with ambient
0.3. What am I doing wrong?  I thought 0.3 isn't a very high value for ambient?

Post a reply to this message

On 2022-02-08 15:38 (-4), tutki wrote:
> I'm testing out 3.8.0-beta.2 and trying out a scene ported from 3.6. Now it's
> complaining "Suspiciously high 'ambient' value found." on textures with ambient
> 0.3. What am I doing wrong?  I thought 0.3 isn't a very high value for ambient?

In POV-Ray 3.6.* and earlier the ambient keyword was often used to
effect a glowing finish.  This usage has been deprecated since POV-Ray
3.7, and 3.8 warns you if it thinks that you are doing that.

If POV-Ray 3.8 guessed correctly, and you want a glowing object, then
replace 'ambient' with 'emission'.

If you really do want ambient 0.3, then add 'emission 0' to that same
finish statement.  This will suppress the warning.

Ambient 0.3 does seem rather high to me, but it's not for me or POV-Ray
to tell you, as an artist, not to use it that high.  The 'emission 0'
tells POV-Ray 3.8 that you have consciously made that choice.

Post a reply to this message

Cousin Ricky <ric### [at] yahoocom> wrote:
[...]
> Ambient 0.3 does seem rather high to me, but it's not for me or POV-Ray
> to tell you, as an artist, not to use it that high.  The 'emission 0'
> tells POV-Ray 3.8 that you have consciously made that choice.

What are typical values for ambient that aren't considered high?

I'm noticing that 3.7 seems to be producing a much brighter image than 3.6. Is
there some global setting that I should be using to make it equivalent to 3.6?
Besides #version, that is. I want to know what's the difference between 3.6 and
3.7 lighting that's causing it to produce a much brighter (almost oversaturated)
image.

Post a reply to this message

On 2022-02-09 07:38 (-4), tutki wrote:
> Cousin Ricky <ric### [at] yahoocom> wrote:
> [...]
>> Ambient 0.3 does seem rather high to me, but it's not for me or POV-Ray
>> to tell you, as an artist, not to use it that high.  The 'emission 0'
>> tells POV-Ray 3.8 that you have consciously made that choice.
> 
> What are typical values for ambient that aren't considered high?
> 
> I'm noticing that 3.7 seems to be producing a much brighter image than 3.6. Is
> there some global setting that I should be using to make it equivalent to 3.6?
> Besides #version, that is. I want to know what's the difference between 3.6 and
> 3.7 lighting that's causing it to produce a much brighter (almost oversaturated)
> image.

Do you have an assumed_gamma in your global_settings?  In 3.6, there was
no default value, so the image defaulted to whatever gamma was used by
your monitor, typically 2.2 or sRGB.  In 3.7+ a warning is given about
the missing assumed_gamma, and it defaults to 1.0.  This causes scenes
with no assumed_gamma to look lighter and washed out when rendered in
3.7+, compared to earlier versions.

The reason for all this is explained in the gamma handling section of
the documentation.
<https://wiki.povray.org/content/Documentation:Tutorial_Section_3.3#Gamma_Handling>

This makes me think that this is the reason 0.3 doesn't seem high to
you.  In older versions of POV-Ray, due to the implicit gamma
conversion, a value of 0.3 translated to a physical brightness of 0.07.
 We are typically unaware of this because our perceptions are nonlinear.

The quickest way to solve this problem is to add global_settings {
assumed_gamma srgb } near the top of your scene file, but this is just a
short term solution.

Longer term, you can replace all your rgb keywords with srgb, which
lowers the brightness of the colors so that they look correct with
assumed_gamma 1.  If you use the named colors from colors.inc, prefix
those names with srgbft.  But you will also have to adjust your lighting
conditions downward.  Adjusting older scene files will be a pain, but
for new scene files, setting up your lighting with assumed_gamma 1
should be simpler than with the old unregulated and nonlinear
2.2/sRGB/1.8 gamma, or whatever.

(Be aware that the srgb series of keywords is not a cure-all, and has
its own traps.  See thread "strange problem with srgb color in
light_source" in povray.general from last March.)

Post a reply to this message

Le 2022-02-08 à 14:38, tutki a écrit :
> I'm testing out 3.8.0-beta.2 and trying out a scene ported from 3.6. Now it's
> complaining "Suspiciously high 'ambient' value found." on textures with ambient
> 0.3. What am I doing wrong?  I thought 0.3 isn't a very high value for ambient?
> 

Any ambient value larger than 0.1 is considered high.

You should add «assumed_gamma 1» in your global_settings block.
Replace ambient with emission everywhere it is larger than 0.1.
It's often also interesting to change any other ambient to 0, or 
commenting out those ambient statements.
The default value for ambient in 3.8 is 0 (zero).

Scene made for version 3.6 and earlier often tend to look washed out 
when using the usual ambient values, and using ambient 0 frequently make 
them look better. That's because the ambient component get added to the 
diffuse component. This can cause channels go beyond 1.

Also, if any of those are radiosity scenes using high ambient as light 
sources, then, those absolutely must be changed to emission. That's 
because, starting with version 3.7, all ambient are turned OFF when 
radiosity is used. Neglecting to do that change will cause everything to 
turn black as there will be no light illuminating anything.

Post a reply to this message

Cousin Ricky <ric### [at] yahoocom> wrote:
[...]
> Do you have an assumed_gamma in your global_settings?  In 3.6, there was
> no default value, so the image defaulted to whatever gamma was used by
> your monitor, typically 2.2 or sRGB.  In 3.7+ a warning is given about
> the missing assumed_gamma, and it defaults to 1.0.  This causes scenes
> with no assumed_gamma to look lighter and washed out when rendered in
> 3.7+, compared to earlier versions.

Aha, indeed this was the problem. I added assumed_gamma 2.2 and now it looks
right. Since this is an old scene, I'll probably just let it be for now. Will
definitely keep this in mind for new scenes.

Thanks!

Post a reply to this message

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

> The default value for ambient in 3.8 is 0 (zero).
>

I also see in the 3.8 included documentation that the default 'diffuse' value is
0.6. But has that always been the case, or did it have a different value in
pre-3.8 versions?

Post a reply to this message

On 2022-02-10 15:01 (-4), Kenneth wrote:
> Alain Martel <kua### [at] videotronca> wrote:
> 
>> The default value for ambient in 3.8 is 0 (zero).
>>
> 
> I also see in the 3.8 included documentation that the default 'diffuse' value is
> 0.6. But has that always been the case, or did it have a different value in
> pre-3.8 versions?

It's been 0.6 since I've used POV-Ray (3.5).  I often increase it in a
#default statement.

Post a reply to this message

On 2022-02-09 12:06 (-4), Alain Martel wrote:
> Le 2022-02-08 à 14:38, tutki a écrit :
>> I'm testing out 3.8.0-beta.2 and trying out a scene ported from 3.6.
>> Now it's
>> complaining "Suspiciously high 'ambient' value found." on textures
>> with ambient
>> 0.3. What am I doing wrong?  I thought 0.3 isn't a very high value for
>> ambient?
>>
> 
> Any ambient value larger than 0.1 is considered high.

I just tested various ambient values with 3.8, and it starts complaining
at 0.3.

Post a reply to this message

Le 2022-02-16 à 12:05, Cousin Ricky a écrit :
> On 2022-02-09 12:06 (-4), Alain Martel wrote:
>> Le 2022-02-08 à 14:38, tutki a écrit :
>>> I'm testing out 3.8.0-beta.2 and trying out a scene ported from 3.6.
>>> Now it's
>>> complaining "Suspiciously high 'ambient' value found." on textures
>>> with ambient
>>> 0.3. What am I doing wrong?  I thought 0.3 isn't a very high value for
>>> ambient?
>>>
>>
>> Any ambient value larger than 0.1 is considered high.
> 
> I just tested various ambient values with 3.8, and it starts complaining
> at 0.3.

If I remember correctly, in the documentation for version 3.5, the 
default ambient value of 0.1 was qualified as «rather large».
Back then, it prompted me to explicitly use smaller values in all of my 
finishes.

Post a reply to this message