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
>
>
>

Post a reply to this message

"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
>
>
>

Post a reply to this message