On 12/01/2014 6:25 PM, clipka wrote:
> Am 12.01.2014 18:54, schrieb MichaelJF:
>
>> I'm not quite sure what we have here. Negative light is a feature
>> which can be
>> used artistically, but then the shadows must be affected too. In your
>> additional
>> scenes the shadows of the positive light still seems to be not
>> influenced by the
>> negative light. Most likely we're hunting down a bug here. My opinion
>> is that
>> negative light gives more artistic freedom but then it must be
>> implemented
>> correctly. For photorealistic renderings it is not necessary. May be
>> Christoph
>> Lipka can shed more light onto this issue.
>
> (I see what you did there :-))
>
> Note that where there is "negative light", there is also "negative
> shadow" - but also note that shadow is nothing but the absence of any
> (in this case negative) light.
>
> The scenes you have posted so far all have the regular shadow lie
> completely inside the "negative shadow", so how should the regular
> shadow be affected by the "negative light"?
>
>

It wasn't Michael that posted the images.
I think of the "negative light" spotlight as being a Souper Dooper Light 
Sooker.

Two further images with the SDLS falling across the true spotlights shadow.
One is intense dark the other has the red component, zero.


> Speaking of necessity for photorealistic renderings, negative light
> would play a role if you wanted to simulate light of highly saturated
> colour, such as from LEDs or mercury vapor lights. Such colours are
> outside of the sRGB gamut (or any other RGB gamut, for that matter), and
> would therefore have to be modeled with one or two colour components
> being negative (unless you have spectral rendering available, that is).
>

I've never been accused of photorealistic renderings. ;-)

> I suspect that there are some places within POV-Ray that can't properly
> handle negative colour components though.
>

The animation I posted just before this one, Needs a flash of reflection 
(?) running down the ribs. I used two concurrent cylinder lights, with 
one of them using "negative light", to make an annular light. It worked 
okay but when I tried to put it in a light group. It just behaved as it 
wasn't in one. :-(

-- 
Regards
     Stephen

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