Orchid XP v7 <voi### [at] devnull> wrote:
> Well... how hard would it be to make is so that if you use a normal 
> object with a nonzero "ambient" setting to make a "light source" in 
> radiosity mode, you get specular hilights?

  Add a reflection and a proper reflection exponent to the object.
To blur the reflection, use the blurred reflection trick.

-- 
                                                          - Warp

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472f7e8a@news.povray.org...
> Orchid XP v7 <voi### [at] devnull> wrote:
>> Now if you could also add feature XYZ as well... ;-)
>
>  If it's not something which will require me to work for a week
> 10 hours a day, or something which will require a rewrite of the
> parser, I'mlistening.

A very useful feature that goes hand in hand with full area lights is color 
mapping aka tone mapping aka exposure control. There's already some code for 
it in Megapov. Basically one needs 3 modes : linear, exponential and HSV 
(plus gamma correction and some others).
http://www.vray.us/vray_documentation/vray_color_mapping_examples.shtml
This is for Vray but it's standard in other renderers. The examples above 
are not very impressive, but HSV color mapping, particularly, is a must have 
for interior scenes.

G.

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Gilles Tran <gitran_nospam_@wanadoo.fr> wrote:
> A very useful feature that goes hand in hand with full area lights is color 
> mapping aka tone mapping aka exposure control.

  I didn't quite get the idea from those images. Some text explaining in
simple terms the idea and the algorithm could be useful.

-- 
                                                          - Warp

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Warp <war### [at] tagpovrayorg> wrote:
> Orchid XP v7 <voi### [at] devnull> wrote:
> > Now if you could also add feature XYZ as well... ;-)
>
>   If it's not something which will require me to work for a week
> 10 hours a day, or something which will require a rewrite of the
> parser, I'mlistening.
>
> --
>                                                           - Warp

Oops, followed this up on the wrong thread...

Two things I'd be interested in:

1) System variables to return the resolution of an input image.  This appears to
be already available in the source code, just not passed on to the SDL.

2) Separate ior for fresnel reflection (in finish block) to allow for better
texture mapping.  I use fresnel quite often, however if I want to map something
like chrome text on a glass block, I would have to model them separately as they
both don't use the same ior.

Just suggestions, however they would be adding to the key word pool.  I've been
wanting to write a patch to do this myself regardless, just don't have the time
to look into how to compile it...

-tgq

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Warp <war### [at] tagpovrayorg> wrote:
> Gilles Tran <gitran_nospam_@wanadoo.fr> wrote:
> > A very useful feature that goes hand in hand with full area lights is color
> > mapping aka tone mapping aka exposure control.
>
>   I didn't quite get the idea from those images. Some text explaining in
> simple terms the idea and the algorithm could be useful.
>
> --
>                                                           - Warp

It looks like tone-mapping, such as what is used with HDR images quite often.
Taking a high range image and remapping it to low range, preserving contrast
and relative colouration without the clamping of the +1 colour intensities.
Seeing as HDR is implemented, it can currently be done using external programs
if HDR output is used.  However, having an internal algorithm would remove the
need for an additional program.  However, the advantage of external programs is
that you have much more control on how you want the mapping to be implemented.
I don't know the particular algorithms involved, but I suspect the ones he is
referring to are quite simple, affecting the whole image uniformly (probably
much the same as gamma correction is implemented to the output image), rather
than being locally dependent.

-tgq

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Trevor G Quayle <Tin### [at] hotmailcom> wrote:
> 1) System variables to return the resolution of an input image.  This appears to
> be already available in the source code, just not passed on to the SDL.

  This should definitely be doable, but I'll have to ask the team about
their opinion. (Cons: Minor feature, increases reserved keyword clutter...)

> 2) Separate ior for fresnel reflection (in finish block) to allow for better
> texture mapping.

  It indeed seems a bit strange that given that reflection is a property of
the texture and not the interior, it would use a value from the interior.
(I don't know the details of the theory behind fresnel reflection, but
I could easily imagine a surface having a different ior on a thin reflecting
layer on its surface than in its main body, thus causing a different type of
reflection than an uniform object would have...)

  Someone who knows the theory behind fresnel reclection could express his
opinion on this.

-- 
                                                          - Warp

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Warp <war### [at] tagpovrayorg> wrote:
> Trevor G Quayle <Tin### [at] hotmailcom> wrote:
> > 1) System variables to return the resolution of an input image.  This appears to
> > be already available in the source code, just not passed on to the SDL.
>
>   This should definitely be doable, but I'll have to ask the team about
> their opinion. (Cons: Minor feature, increases reserved keyword clutter...)

This I understand, and it is something that maybe a lot of users wouldn't use.
Personally I have had a couple of situations where it could be of use lately.

> > 2) Separate ior for fresnel reflection (in finish block) to allow for better
> > texture mapping.
>
>   It indeed seems a bit strange that given that reflection is a property of
> the texture and not the interior, it would use a value from the interior.
> (I don't know the details of the theory behind fresnel reflection, but
> I could easily imagine a surface having a different ior on a thin reflecting
> layer on its surface than in its main body, thus causing a different type of
> reflection than an uniform object would have...)
>
>   Someone who knows the theory behind fresnel reclection could express his
> opinion on this.
>
> --
>                                                           - Warp

Well there is a relationship between the refraactive ior and fresnel reflection
(it's a bit more complex than presented, literally, as a complex number
component is involved, at least from my limited understanding).  It does indeed
seem a propery that is applicable to the interior workings of a material, so I
can see whay it it is outside the texture block, however, the capability for
texture mapping (with reflection being a texture property) would infer that if
ior is related to fresnel, which is related to texture, then ior should be
texture level.  So the solution would be either:
1) move ior to texture.  This would likely be the simplest to achieve (other
than backward compatibility considerations) And also give the side effect of
being extended to refraction for artistic effect.
2) add an additional ior for fresnel refraction only.  This would add a reserved
keyword and require the splitting of the usage of ior for refraction and
reflection.

Alternatively a third option would be:
3) Leave everything as is and make me use a different technique to achieve my
results.  (it is only a suggestion, so I don't fully expect it to be added at
this stage in the beta development)

All-in-all, perhaps the fresnel model needs to be examined a little closer for
better implementation in POV4.

Thanks for the consideration regardless.

-tgq

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Warp wrote:
> Gilles Tran <gitran_nospam_@wanadoo.fr> wrote:
>> A very useful feature that goes hand in hand with full area lights is color 
>> mapping aka tone mapping aka exposure control.
> 
>   I didn't quite get the idea from those images. Some text explaining in
> simple terms the idea and the algorithm could be useful.

Check Graphic Gems IV pp. 391-397 (A contrast-based scale factor for
luminance display).

	Thorsten

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Thorsten Froehlich wrote:
> Warp wrote:
>> Gilles Tran <gitran_nospam_@wanadoo.fr> wrote:
>>> A very useful feature that goes hand in hand with full area lights is color 
>>> mapping aka tone mapping aka exposure control.
>>   I didn't quite get the idea from those images. Some text explaining in
>> simple terms the idea and the algorithm could be useful.
> 
> Check Graphic Gems IV pp. 391-397 (A contrast-based scale factor for
> luminance display).

Online try <http://www.cg.tuwien.ac.at/research/theses/matkovic/node34.html>
and also follow the "Up" link for other methods.

	Thorsten

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Gilles Tran schrieb:
> 
> A very useful feature that goes hand in hand with full area lights is color 
> mapping aka tone mapping aka exposure control. There's already some code for 
> it in Megapov. Basically one needs 3 modes : linear, exponential and HSV 
> (plus gamma correction and some others).
> [...]

Just because a certain renderer offer such three predefined modes does 
not make it a particularly good choice i think.  MegaPOV gives you the 
option of defining any tone mapping function although this currently is 
limited to  a 1D function identical for all color channels.  It might be 
interesting to make this a more general feature allowing full control 
over the mapping in all three color channels or alternatively integrate 
a color management system like LCMS.  It is questionable however 
considering the design of POV-Ray that having this as part of the 
renderer would be particularly useful.  Usually you want to be able to 
control color mapping after the render.  One practical problem about 
doing this separately is that a lot of current software designed for 
such purposes is developed for digital photo processing and often not 
able to load other input images than raw files from digital cameras.

-- Christoph

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