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St. wrote:
> "Mike Raiford" <mra### [at] hotmail com> wrote in message
> news:464c5ab1$1@news.povray.org...
>
>> Is it possible to post a minimal scene that reproduces the blue shadow..?
>> I'm curious, now.
>
> I think it's my assumed_gamma Mike. I've just tried it with 2.2 which
> makes the whole image too dark (but the shadow looks ok), and 1, and that's
> better, but still too dark, (now with a darker blue shadow). At .75, the
> overall image looks fine, (the right brightness, contrast, etc.), apart from
> the blue shadow.
>
> Hmm, what to do, what to do...
>
> ~Steve~
Hm. The code you included with this post doesn't exhibit much of
anything, just a gray fog with a darker gray background.
What version of POVRay are you using?
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"Mike Raiford" <mra### [at] hotmailcom> wrote in message
news:464c6ff6@news.povray.org...
> St. wrote:
>> "Mike Raiford" <mra### [at] hotmailcom> wrote in message
>> news:464c5ab1$1@news.povray.org...
> Hm. The code you included with this post doesn't exhibit much of anything,
> just a gray fog with a darker gray background.
That's all there is apart from Wings models and some PovTree's. As it is
now, the scene looks quite good and I'm happy with it, I'm just not getting
the assumed_gamma thing. It's confusing me because it should either be 2.2
or 1 (from what I've read). FWIW, nearly all of my images over the last two
years use a low assumed_gamma. Where am I going wrong with this?
>
> What version of POVRay are you using?
Yes, sorry, 3.5.
~Steve~
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Are you using radiosity? A blue sky
can tint the fog blue if you are using
radiosity.
What are the textures? Are any reflective?
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"Tim Attwood" <tim### [at] comcastnet> wrote in message
news:464d1426@news.povray.org...
> Are you using radiosity? A blue sky
> can tint the fog blue if you are using
> radiosity.
No radiosity and I've removed my sky_sphere - no difference.
>
> What are the textures? Are any reflective?
The textures are image maps with bump mapping and the only thing that's
reflective is a small model which I don't think would make a difference.
I've settled for having the assumed_gamma at 1.2, which makes the
scene/shadow better, but darker overall.
~Steve~
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St. wrote:
> Hi all
>
> Need a little help and advice if possible.
Steve,
Does your fog use color filtering? If yes, try to use it without. In
addition to raising the assumed_gamma, try increasing the intensity of
your light to compensate. Failing that, make sure all your objects are
hollow, as this can sometimes result in weird fog effects, not just
complete absence. Beyond these things, there are a bunch of other things
you could try. The first that comes to mind is a transparent (and
hollow) sphere around the camera with a transmit greater than 1. This
will bump up the contrast of the image, and may give you the results you
want (at the expense of render time). The good thing about POV-Ray is
that there are usually a number of ways to arrive at a desired result.
Try anything that sounds like it might be useful!
~Sam
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"St." <dot### [at] dotcom> wrote in message news:464c7fdb$1@news.povray.org...
>
> That's all there is apart from Wings models and some PovTree's. As it is
> now, the scene looks quite good and I'm happy with it, I'm just not
> getting the assumed_gamma thing. It's confusing me because it should
> either be 2.2 or 1 (from what I've read). FWIW, nearly all of my images
> over the last two years use a low assumed_gamma. Where am I going wrong
> with this?
assumed_gamma should be 1 for the best simulation of light. Povray will
gamma correct the image from the "assumed" gamma to the "actual" gamma which
is stored in one of it's ini files. The ini file value is 2.2 so if you want
no gamma correction use the (default) assumed_gamma 2.2. But, light by
definition has linear gamma, whereas monitors have non-linear gamma (50%
grey is not half the brightness of white on a monitor), so assumed_gamma 1
tells pov to do all it's maths as if they have a gamma of 1, then to
implicitly correct that to a gamma of 2.2 for the image. It's VERY counter
intuitive!
I've tried your source with a simple scene and I can't get any blue.
assumed_gamma won't be the cause, it will just be adjusting the brightness
of the error. Has anything in the scene got negative colour values? e.g.
negative ambient light?
--
Tek
http://evilsuperbrain.com
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"Samuel Benge" <stb### [at] hotmailcom> wrote in message
news:46531d8b@news.povray.org...
Beyond these things, there are a bunch of other things
> you could try. The first that comes to mind is a transparent (and hollow)
> sphere around the camera with a transmit greater than 1. This will bump up
> the contrast of the image, and may give you the results you want (at the
> expense of render time).
AHA! Thank you for this tip Sam! I've tried it and it works, well, it's
given me the extra option of adjusting both the transmit (around the camera)
and the assumed_gamma at the same time, and I've found a combination that
takes a lot of the blue away whilst leaving a nice contrast. Brilliant! :o)
~Steve~
> ~Sam
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"Tek" <tek### [at] evilsuperbraincom> wrote in message
news:46542d56$1@news.povray.org...
> "St." <dot### [at] dotcom> wrote in message news:464c7fdb$1@news.povray.org...
>>
>> That's all there is apart from Wings models and some PovTree's. As it is
>> now, the scene looks quite good and I'm happy with it, I'm just not
>> getting the assumed_gamma thing. It's confusing me because it should
>> either be 2.2 or 1 (from what I've read). FWIW, nearly all of my images
>> over the last two years use a low assumed_gamma. Where am I going wrong
>> with this?
>
> assumed_gamma should be 1 for the best simulation of light. Povray will
> gamma correct the image from the "assumed" gamma to the "actual" gamma
> which is stored in one of it's ini files. The ini file value is 2.2 so if
> you want no gamma correction use the (default) assumed_gamma 2.2. But,
> light by definition has linear gamma, whereas monitors have non-linear
> gamma (50% grey is not half the brightness of white on a monitor), so
> assumed_gamma 1 tells pov to do all it's maths as if they have a gamma of
> 1, then to implicitly correct that to a gamma of 2.2 for the image. It's
> VERY counter intuitive!
Hmm, now I get it, thanks Tek, I think I'll leave it at 1 from now on
and use Sam' trick too.
>
> I've tried your source with a simple scene and I can't get any blue.
> assumed_gamma won't be the cause, it will just be adjusting the brightness
> of the error. Has anything in the scene got negative colour values? e.g.
> negative ambient light?
No, not a negative ambient light, but my ground texture is negative,
would that also create that blue in combination with the fog? I'll have a
play and see what happens.
~Steve~
>
> --
> Tek
> http://evilsuperbrain.com
>
>
>
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"St." <dot### [at] dotcom> wrote in message news:4657fb3d@news.povray.org...
>
> No, not a negative ambient light, but my ground texture is negative,
> would that also create that blue in combination with the fog? I'll have a
> play and see what happens.
Yep, grey fog - yellow ground texture = blue
Povray's accurately calculating something impossible!
--
Tek
http://evilsuperbrain.com
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"Tek" <tek### [at] evilsuperbraincom> wrote in message
news:4657fe25@news.povray.org...
> "St." <dot### [at] dotcom> wrote in message news:4657fb3d@news.povray.org...
>>
>> No, not a negative ambient light, but my ground texture is negative,
>> would that also create that blue in combination with the fog? I'll have a
>> play and see what happens.
>
> Yep, grey fog - yellow ground texture = blue
>
> Povray's accurately calculating something impossible!
Ok, now we're getting closer, and if I play with my texture some more, I
should be able to eliminate it altogether and get something satisfactory.
TY. :)
~Steve~
>
> --
> Tek
> http://evilsuperbrain.com
>
>
>
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