"Anthony D. Baye" <Sha### [at] spamnomorehotmailcom> wrote:
> So I guess the question is: Does the emission keyword supercede ambient?

It doesn't supersede ambient per se, but supersedes one particular ad hoc usage
of ambient, which was to cause objects to glow.

The rule of thumb for POV-Ray 3.7 is that if your object glows in the dark, use
emission.  If it doesn't, use ambient.

> should
> the textures in the libraries be updated to reflect that?

I would say no, because then you'd have everything glowing when radiosity is
used.  This was already a problem with the stock textures in POV-Ray 3.6
(especially with the metals), though not everyone may have noticed it.

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Am 30.11.2014 15:25, schrieb Robert McGregor:
> "Anthony D. Baye" <Sha### [at] spamnomorehotmailcom> wrote:
>> I have six light sources.  There is no difference in lighting between the two
>> samples. Granted the part I'm wondering about is in moderate shadow, but it
>> should be receiving some of the light.  The primary texture is at least the same
>> color when rendered with radiosity, which indicates to me that the color of the
>> secondary relies too much on it's ambient value.
>
> Adding to the finish(es) an emission value that matches the existing ambient
> value should fix that issue completely when using radiosity.

Uh... don't! That would just be a nasty workaround, not a solution.

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Am 30.11.2014 18:40, schrieb Anthony D. Baye:

> So I guess the question is: Does the emission keyword supercede ambient? should
> the textures in the libraries be updated to reflect that?

Absolutely not - while technically ambient and emission essentially do 
the same thing, they reflect two entirely different use cases, which the 
previous ambient-only mechanism could not both cater for simultaneously 
without different material definitions for radiosity and non-radiosity 
scenes.

As a matter of fact, the two have been separated in POV-Ray 3.7 so that 
carefully designed textures can now be used for both radiosity and 
non-radiosity renders alike without change; the key is to design the 
texture to work in a radiosity scene first (for reflective materials 
make sure to use a light probe in your testing environment or otherwise 
provide some environment to reflect), then add some ambient to lighten 
up shadows in non-radiosity renders.

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clipka <ano### [at] anonymousorg> wrote:
> Am 30.11.2014 15:25, schrieb Robert McGregor:
> > Adding to the finish(es) an emission value that matches the existing ambient
> > value should fix that issue completely when using radiosity.
>
> Uh... don't! That would just be a nasty workaround, not a solution.

I completely agree it's not the "right" way to go about it, but it is a "quick
fix" for such a problem as he originally described. For example, here is "Basic
Scene 10 - Night moon partly cloudy sky:"

1) the top image is the original (non-radiosity)

2) the middle version uses a default radiosity {} block without changing
anything else

3) the bottom is the same as #2 but replacing ambient with emission. Quick fix.
Not identical, but to my eye renders using radiosity always looks better anyway.

-------------------------------------------------
www.McGregorFineArt.com

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Preview of image 'basicscene10.png'

"Anthony D. Baye" <Sha### [at] spamnomorehotmailcom> wrote:

> and thanks for the tips on HDRI.  Now I just need a step-by-step tutorial on how
> to use it in scene.

There's not much to it really:

1) To create an HDR image for use as IBL just render your scene with a spherical
camera; here's the default from the Insert menu:

camera {
  spherical
  location <0,0,0>      // position
  look_at  <0,0,1>      // view
  angle 360             // horizontal degrees
        180             // vertical degrees
}

Render the scene using command-line (for example) +fe +w2048 +h1024 to produce
an EXR image.

2) Then you can use this resulting EXR image as the IBL for any scene by
wrapping it on a huge sphere to act as the environment lighting, something like
(assuming radiosity):

sphere { 0, 10000 hollow inverse
   pigment { image_map { exr "SomeEXR" interpolate 3 map_type 1 }}
   finish { emission 2 diffuse 0 }
}

If there are any unwanted speckle-artifacts from the EXR lighting in a scene
(likely due to sampling errors over very large differences in neighboring pixel
colors) I make a smaller, heavily blurred version of the EXR in GIMP or PS and
use that instead, say 512x256 pixels.

-------------------------------------------------
www.McGregorFineArt.com

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> clipka <ano### [at] anonymousorg> wrote:
>> Am 30.11.2014 15:25, schrieb Robert McGregor:
>>> Adding to the finish(es) an emission value that matches the existing ambient
>>> value should fix that issue completely when using radiosity.
>>
>> Uh... don't! That would just be a nasty workaround, not a solution.
>
> I completely agree it's not the "right" way to go about it, but it is a "quick
> fix" for such a problem as he originally described. For example, here is "Basic
> Scene 10 - Night moon partly cloudy sky:"
>
> 1) the top image is the original (non-radiosity)
>
> 2) the middle version uses a default radiosity {} block without changing
> anything else
>
> 3) the bottom is the same as #2 but replacing ambient with emission. Quick fix.
> Not identical, but to my eye renders using radiosity always looks better anyway.
>
> -------------------------------------------------
> www.McGregorFineArt.com
>

This is a special case where ambient was used to make the sky glow. In 
/THIS/ particuliar case, replacing ambient by emission is correct as 
this texture *is* meant to be a source of illumination.
There are a few similar textures, like the lightnings and various skys 
as well as the "Luminous" finish.



Alain

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