POV-Ray : Newsgroups : povray.beta-test : skyspheres transmit of color maps not computed last : Re: skyspheres transmit of color maps not computed last Server Time
28 Sep 2024 14:54:31 EDT (-0400)
  Re: skyspheres transmit of color maps not computed last  
From: Le Forgeron
Date: 27 Oct 2010 08:28:09
Message: <4cc81ad9$1@news.povray.org>
Le 26/10/2010 23:49, Mr a écrit :
> "Mr" <nomail@nomail> wrote:
>> If I do that,  only the last entry of color map of my gradient will be used as
>> if the the first entry had never existed. so it seems like the transparency is
>> baked into the color for each entry. could there be an option to make it so that
>> if the first entry has transmit 1 its color is still retained and all
>> transparencies
>> only applied in the alpha layer?
> 
> Actually it's not the color of the last entry, it happened to be the color of my
> background too. If I remove the background, I get a completely black skysphere!
> So what is happening, Are spy sphere totally ignoring the separation between
> colors and alpha?
> 
> 

You are specifying a transmit of 1, which means that the ray must goes
straight through the sky_sphere, without interacting with the colour.
Hence it get to the background... whose default is black unless you
specify another.

I'm afraid we are entering the big discussion in image format: does a
transparent pixel have a colour (or: is the rgb part of an alpha-enabled
image format pre-multiplied or not in regard to alpha (and gamma, it's
far more fun with gamma in the equation)).

The problem is that different format have different answers.
(and they might be all valid, up to their tenants)

Maybe you want to replace rgbt with rgbf (it give a colored background
with some transparency with +UA (and using a format which support alpha,
such as png)) ?

Or keep rgbt, but reduces t to 0.5 ?

I do not get what you are trying to achieve with such transmitting
sky_sphere.

-- 
Real software engineers work from 9 to 5, because that is<br/>
the way the job is described in the formal spec.  Working<br/>
late would feel like using an undocumented external procedure.


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