Hello everybody

I'm trying some test with HDR lighting, using the example shown in this thread:
http://news.povray.org/povray.general/thread/%3Cweb.4e316b7b630a1fa94c0a951f0%40news.povray.org%3E

I have commented the following sky_sphere block:

sky_sphere {
  pigment {image_map {hdr "*HDR_FILE_PATH.hdr*" map_type 1 interpolate 2}}
  rotate y*-120
}

and added this instead:

sphere {
  <0,0,0>, 10000
  pigment {image_map {hdr "*HDR_FILE_PATH.hdr*" map_type 1 interpolate 2}}
  rotate y*-120
  hollow
}

(this is as suggested in another thread, to be able to maintain the lighting of
the chosen hdr file while showing some other image mapped on the sky_sphere).

I expected to obtain the same result at this point, on the contrary I get a much
darker image (so lighting must be substantially different) and also an array" of
evenly spaced irregularly-shaped "blots" over the image.

Could someone please explain what is happening?
I've read docs about sky_sphere, but I did not understand why it should give
such different lighting results... To my understanding it should just be
enclosing anything else in the scene...

Thanks in advance,
Alessandro

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Le 21/12/2011 17:17, acasta nous fit lire :
> Hello everybody
> 
> I'm trying some test with HDR lighting, using the example shown in this thread:
>
http://news.povray.org/povray.general/thread/%3Cweb.4e316b7b630a1fa94c0a951f0%40news.povray.org%3E
> 
> I have commented the following sky_sphere block:
> 
> sky_sphere {
>   pigment {image_map {hdr "*HDR_FILE_PATH.hdr*" map_type 1 interpolate 2}}
>   rotate y*-120
> }
> 
> and added this instead:
> 
> sphere {
>   <0,0,0>, 10000
>   pigment {image_map {hdr "*HDR_FILE_PATH.hdr*" map_type 1 interpolate 2}}
>   rotate y*-120
>   hollow
> }
> 

> I expected to obtain the same result at this point, on the contrary I get a much
> darker image (so lighting must be substantially different) and also an array" of
> evenly spaced irregularly-shaped "blots" over the image.
> 
> Could someone please explain what is happening?


what is your finish on the sphere ? (hint: unless you use something
along "ambient 1.0 diffuse 0.0 ... ", the aspect of the texture/pigment
on a point of the sphere is subject to reachability by a light source,
and the relevant light that it gets.)

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Am 21.12.2011 17:17, schrieb acasta:

> I expected to obtain the same result at this point, on the contrary I get a much
> darker image (so lighting must be substantially different) and also an array" of
> evenly spaced irregularly-shaped "blots" over the image.
>
> Could someone please explain what is happening?

Yup: Sky spheres can be thought of as having an "emission 1 ambient 0 
diffuse 0 specular 0 reflection 0" finish; note that this differs from 
the default finish for normal objects, which is primarily diffuse, so 
you'll have to specify these finish properties explicitly on your pseudo 
sky sphere.

As for the blots, they're most likely radiosity artifacts and will 
disappear once you set diffuse to 0.

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Thanks for your suggestions.

The finish block with settings described by clipka did the job.
I didn't know about the "hidden" properties of sky_sphere...
Great!
Alessandro

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