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Rune <run### [at] iname com> wrote:
: When you have turned the alpha channel on in POV-Ray, one must expect it to
: be first priority that the image works correctly *with* alpha channel
: support.
What is the correct behaviour?
For example, let's suppose that we are calculating a pixel which is
located at the crossing of the edges of two objects.
One object is red (<1,0,0>) and takes 50% of the pixel area. The other
object is green (<0,1,0>) and takes 25% of the pixel area. The last 25%
of the pixel is background.
What should be the RGBA values for that pixel?
--
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/
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On Sun, 24 Sep 2000 01:18:33 +0200, "Rune" <run### [at] iname com>
wrote:
>When you have turned the alpha channel on in POV-Ray, one must expect it to
>be first priority that the image works correctly *with* alpha channel
>support.
Rune, the way POV works *is* the correct way. If you don't like it,
you can always remove the black/white matte or defringe it in
PhotoShop. It will take care of removing the leftovers from the
background based on the alpha channel intensity.
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usa net
TAG e-mail : pet### [at] tag povray org
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"Warp" wrote:
> What is the correct behaviour?
>
> For example, let's suppose that we are calculating a pixel
> which is located at the crossing of the edges of two objects.
> One object is red (<1,0,0>) and takes 50% of the pixel area.
> The other object is green (<0,1,0>) and takes 25% of the pixel
> area. The last 25% of the pixel is background.
> What should be the RGBA values for that pixel?
After the method *I* think is correct:
Colour: 0.67*red + 0.33*green => <0.67,0.33,0.00>
Alpha: 0.50*1 + 0.25*1 + 0.25*0 => 0.75
When you in a paint program put a background colour behind the image layer
the final colour value of the pixel will be like this:
image_colour*0.75 + background_colour*0.25
If the bg_colour is black the final colour will be: <0.50,0.25,0.00>
But if the background colour is white the colour will be: <0.75,0.50,0.25>
So no matter what colour you put behind your image the antialiasing will
work nicely without leaving any hint of what background colour you
originally used in POV-Ray. That is what I think is correct behaviour.
I'll make some images that shows what I mean and post them to
povray.binaries.images...
Rune
--
\ Include files, tutorials, 3D images, raytracing jokes,
/ The POV Desktop Theme, and The POV-Ray Logo Contest can
\ all be found at http://rsj.mobilixnet.dk (updated July 23)
/ Also visit http://www.povrayusers.org
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"Peter Popov" wrote:
> Rune, the way POV works *is* the correct way. If you don't like it,
> you can always remove the black/white matte or defringe it in
> PhotoShop. It will take care of removing the leftovers from the
> background based on the alpha channel intensity.
Why is an external program necessary to remove the traces of the background
I used in POV-Ray? I don't have PhotoShop.
Rune
--
\ Include files, tutorials, 3D images, raytracing jokes,
/ The POV Desktop Theme, and The POV-Ray Logo Contest can
\ all be found at http://rsj.mobilixnet.dk (updated July 23)
/ Also visit http://www.povrayusers.org
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Peter Popov wrote:
>
> On Sun, 24 Sep 2000 01:18:33 +0200, "Rune" <run### [at] iname com>
> wrote:
>
> >When you have turned the alpha channel on in POV-Ray, one must expect it to
> >be first priority that the image works correctly *with* alpha channel
> >support.
>
> Rune, the way POV works *is* the correct way. If you don't like it,
> you can always remove the black/white matte or defringe it in
> PhotoShop. It will take care of removing the leftovers from the
> background based on the alpha channel intensity.
>
At the edges of objects the rgb values of the object are AAed with the
background colour. When I turn on transparency, it's because I want the
background to represent _nothing_, how can nothing have a colour? There
should be no leftovers to remove.
PoD.
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"PoD" wrote:
> At the edges of objects the rgb values of the object are AAed
> with the background colour. When I turn on transparency, it's
> because I want the background to represent _nothing_, how can
> nothing have a colour? There should be no leftovers to remove.
Exactly. The background presence should be stored in the alpha
channel only. Not in the red, green and blue components.
I have posted an image to povray.binaries.images and a bug report
to povray.bugreports
Rune
--
\ Include files, tutorials, 3D images, raytracing jokes,
/ The POV Desktop Theme, and The POV-Ray Logo Contest can
\ all be found at http://rsj.mobilixnet.dk (updated August 7)
/ Also visit http://www.povrayusers.org
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On Sun, 24 Sep 2000 22:19:02 +0200, Rune wrote:
>Exactly. The background presence should be stored in the alpha
>channel only. Not in the red, green and blue components.
>
>I have posted an image to povray.binaries.images and a bug report
>to povray.bugreports
It might have been premature for a post to .bugreports (we'll see; if it's
approved, it wasn't premature :) ) but for what it's worth, I agree that it
should work the way you describe rather than the way it works now.
--
Ron Parker http://www2.fwi.com/~parkerr/traces.html
My opinions. Mine. Not anyone else's.
Proudly not helping RIAA and SDMI steal my rights --
http://www.eff.org/Misc/EFF/Newsletters/EFFector/HTML/effect13.08.html
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In article <slr### [at] fwi com> , ron### [at] povray org (Ron
Parker) wrote:
>>I have posted an image to povray.binaries.images and a bug report
>>to povray.bugreports
>
> It might have been premature for a post to .bugreports (we'll see; if it's
> approved, it wasn't premature :) ) but for what it's worth, I agree that it
> should work the way you describe rather than the way it works now.
I replied to the image post in povray.binaries.images and suggested to post
it as bug report :-)
Thorsten
____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trf de
Visit POV-Ray on the web: http://mac.povray.org
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On Sun, 24 Sep 2000 12:15:59 +0200, "Rune" <run### [at] iname com>
wrote:
>Why is an external program necessary to remove the traces of the background
>I used in POV-Ray?
These are not traces of the background. These are the actual colors of
the pixels. If the edge of red sphere on a blue background takes only
10% of a pixel, then this pixel will have a color of <0.1,0,0.9> . If
you make it <1,0,0>, antialiasing will be totally useless as no
jaggies will be reduced.
>I don't have PhotoShop.
I only used it as an example.
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usa net
TAG e-mail : pet### [at] tag povray org
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On Sun, 24 Sep 2000 22:19:02 +0200, "Rune" <run### [at] iname com>
wrote:
>"PoD" wrote:
>> At the edges of objects the rgb values of the object are AAed
>> with the background colour. When I turn on transparency, it's
>> because I want the background to represent _nothing_, how can
>> nothing have a colour? There should be no leftovers to remove.
>
>Exactly. The background presence should be stored in the alpha
>channel only. Not in the red, green and blue components.
So, when anti-aliasing, how should POV treat rays that hit the
background? Ignore them?
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usa net
TAG e-mail : pet### [at] tag povray org
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