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From: Christoph Hormann
Subject: Re: Anti-Aliasing Problem including sample image (58k)
Date: 27 Nov 2002 05:00:53
Message: <3DE497D5.5B052B6B@gmx.de>
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Rene Schwietzke wrote:
>
> Hi Christoph,
>
> I checked the code and saw the linear interpolation algorithm. Therefore I
> expected an unsolvable problem but the discussion above shows, that it might
> be a defect. Could LAB solve the problem as discussed before? It seems to be
> fine for Photoshop but it could be protected by copyrights...
Doing color interpolation in CIE color space could indeed help but
conversion isn't easy. A google search for 'CIE color interpolation' or
something similar will spit out a lot of material. It might be easier
though to simply implement some nonlinear interpolation in RGB space
instead, this could be easily adjusted too.
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 15 Nov. 2002 _____./\/^>_*_<^\/\.______
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From: Rene Schwietzke
Subject: Re: Anti-Aliasing Problem including sample image (58k)
Date: 27 Nov 2002 05:25:47
Message: <3de49dab$1@news.povray.org>
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Hi,
the ImageMagick (http://www.imagemagick.org) source can be accessed...a way
to borrow a few ideas?
Rene
--
Rene Schwietzke
r.schwietzke<at>reneschwietzke.de
http://www.rene-schwietzke.de/
"Christoph Hormann" <chr### [at] gmx de> wrote in message
news:3DE497D5.5B052B6B@gmx.de...
>
> Doing color interpolation in CIE color space could indeed help but
> conversion isn't easy. A google search for 'CIE color interpolation' or
> something similar will spit out a lot of material. It might be easier
> though to simply implement some nonlinear interpolation in RGB space
> instead, this could be easily adjusted too.
>
Post a reply to this message
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> I just checked, and indeed, POV-Ray seems to be antialiasing after gamma
> correction. Bad!! This should really be fixed, but as a workaround, you can
> render with Display_Gamma=1.0 and then manually gamma-correct the image by
> 2.2.
>
Strange. I've checked it and it seems to work, but I do not understand why.
From my knowledge, simple color blending within the RGB color space
should always give that unwanted result, and I do not see what gamma
correction has to do with it. Can somebody please enlighten me.
-Ive
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From: Anders K
Subject: Re: Anti-Aliasing Problem including sample image (58k)
Date: 27 Nov 2002 11:22:13
Message: <3de4f135@news.povray.org>
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Ive wrote:
> Strange. I've checked it and it seems to work, but I do not understand
why.
> From my knowledge, simple color blending within the RGB color space
> should always give that unwanted result, and I do not see what gamma
> correction has to do with it. Can somebody please enlighten me.
Suppose we're just "antialiasing" two pixels together, purple and cyan --
that is, rgb <1, 0, 1> and rgb <0, 1, 1>. If we antialias and then
gamma-correct, we get <0.730, 0.730, 1> which the monitor turns into <0.500,
0.500, 1>, the color halfway between purple and cyan. However, if we
gamma-correct and then antialias (as POV-Ray does), we get <0.500, 0.500, 1>
which the monitor turns into about <0.218, 0.218, 1> -- resulting in the
blue line.
Anders
P.S. Here's the original image gamma-corrected by 2.2. As you can see, the
unwanted colors are gone.
--
light_source{6#local D=#macro B(E)#macro A(D)#declare E=(E-#declare
C=mod(E D);C)/D;C#end#while(E)#if(A(8)=7)#declare D=D+2.8;#else#if(
C>2)}torus{1..2clipped_by{box{-2y}}rotate<1 0C>*90translate<D+1A(2)
*2+1#else}cylinder{0(C-v=1).2translate<D+C*A(2)A(4)#end-2 13>finish
{specular 1}pigment{rgb x}#end#end#end-8;1B(445000298)B(519053970)B
(483402386)B(1445571258)B(77778740)B(541684549)B(42677491)B(70)}
Post a reply to this message
Attachments:
Download 'aa-sample.png' (56 KB)
Preview of image 'aa-sample.png'
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From: Ive
Subject: Re: Anti-Aliasing Problem including sample image (58k)
Date: 27 Nov 2002 13:05:30
Message: <3de5096a@news.povray.org>
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> Suppose we're just "antialiasing" two pixels together, purple and cyan --
> that is, rgb <1, 0, 1> and rgb <0, 1, 1>. If we antialias and then
> gamma-correct, we get <0.730, 0.730, 1> which the monitor turns into <0.500,
> 0.500, 1>, the color halfway between purple and cyan. However, if we
> gamma-correct and then antialias (as POV-Ray does), we get <0.500, 0.500, 1>
> which the monitor turns into about <0.218, 0.218, 1> -- resulting in the
> blue line.
>
Well, I already got it by thinking a little more about the problem (as always
first thinking then posting) but anyway thanks a lot.
-Ive
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From: Anders K
Subject: Re: Anti-Aliasing Problem including sample image (58k)
Date: 27 Nov 2002 13:48:19
Message: <3de51373$1@news.povray.org>
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I posted a patch for this problem in povray.programming.
Subject: Apply gamma correction after antialiasing
<http://news.povray.org/3de5126d$1@news.povray.org>
For this patch to work, make sure you set global_settings { assumed_gamma
1.0 } in your scene.
Anders
--
light_source{6#local D=#macro B(E)#macro A(D)#declare E=(E-#declare
C=mod(E D);C)/D;C#end#while(E)#if(A(8)=7)#declare D=D+2.8;#else#if(
C>2)}torus{1..2clipped_by{box{-2y}}rotate<1 0C>*90translate<D+1A(2)
*2+1#else}cylinder{0(C-v=1).2translate<D+C*A(2)A(4)#end-2 13>finish
{specular 1}pigment{rgb x}#end#end#end-8;1B(445000298)B(519053970)B
(483402386)B(1445571258)B(77778740)B(541684549)B(42677491)B(70)}
Post a reply to this message
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