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From: stevenvh
Subject: color differences when doing partial renderings
Date: 12 Jan 2011 03:25:01
Message: <web.4d2d6477d935f551c0721a1d0@news.povray.org>
I wanted to create a rather large image (19050x7620) but v37 RC2 failed to
finish the rendering, so I had to create partial renderings and stitch them
together; I'm using Photoshop for this.
After stitching I noticed minute differences in color either side of the seam,
for instance #404013 on one side and #3F3E12 on the other. This doesn't seem
much, but along a straight line this is clearly visible. Shouldn't a pixel's
color be independent of other (rendered or not) pixels surrounding it?


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From: stevenvh
Subject: Re: color differences when doing partial renderings
Date: 12 Jan 2011 03:30:00
Message: <web.4d2d65eec935e0c5c0721a1d0@news.povray.org>
"stevenvh" <nomail@nomail> wrote:
> I wanted to create a rather large image (19050x7620) but v37 RC2 failed to

That's v3.7 RC2, of course.


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From: Le Forgeron
Subject: Re: color differences when doing partial renderings
Date: 12 Jan 2011 04:17:33
Message: <4d2d71ad$1@news.povray.org>
Le 12/01/2011 09:21, stevenvh a écrit :
> Shouldn't a pixel's
> color be independent of other (rendered or not) pixels surrounding it?
> 
Are you rendering with AA ?
Only -A (disabling AA) would not look around for other "pixels"

there is more option about Antialiasing (AA), see

http://wiki.povray.org/content/Documentation:Reference_Section_1.3#Anti-Aliasing_Options

Jitter amount may play a role too.


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From: stevenvh
Subject: Re: color differences when doing partial renderings
Date: 12 Jan 2011 06:25:00
Message: <web.4d2d8eedc935e0c5c0721a1d0@news.povray.org>
Le_Forgeron <lef### [at] freefr> wrote:
> Le 12/01/2011 09:21, stevenvh a écrit :
> > Shouldn't a pixel's
> > color be independent of other (rendered or not) pixels surrounding it?
> >
> Are you rendering with AA ?
> Only -A (disabling AA) would not look around for other "pixels"
>

I agree that anti-alias influences adjacent pixels, but this stretches over more
than 50 pixels, and that's a bit much, even for AA, isn't it?
I just started a new rendering, without AA. It will take some time to finish.
I'll post it here if the results are any better.


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From: Nekar Xenos
Subject: Re: color differences when doing partial renderings
Date: 12 Jan 2011 06:50:09
Message: <op.vo61thq7ufxv4h@go-dynamite>
On Wed, 12 Jan 2011 13:23:50 +0200, stevenvh <nomail@nomail> wrote:

> Le_Forgeron <lef### [at] freefr> wrote:
>> Le 12/01/2011 09:21, stevenvh a écrit :
>> > Shouldn't a pixel's
>> > color be independent of other (rendered or not) pixels surrounding 
it?
>> >
>> Are you rendering with AA ?
>> Only -A (disabling AA) would not look around for other "pixels"
>>
>
> I agree that anti-alias influences adjacent pixels, but this stretches
  

> over more
> than 50 pixels, and that's a bit much, even for AA, isn't it?
> I just started a new rendering, without AA. It will take some time to 
 

> finish.
> I'll post it here if the results are any better.
>

Are you using radiosity?

-- 

-Nekar Xenos-


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From: stevenvh
Subject: Re: color differences when doing partial renderings
Date: 12 Jan 2011 08:35:00
Message: <web.4d2dad4ec935e0c5c0721a1d0@news.povray.org>
"Nekar Xenos" <nek### [at] gmailcom> wrote:
> Are you using radiosity?
>

Yes, I am, but as I understand it radiosity influences pixels color through the
object's color in the scene, not the (adjacent) pixels in the image.


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From: stevenvh
Subject: Re: color differences when doing partial renderings
Date: 12 Jan 2011 11:25:00
Message: <web.4d2dd4d2c935e0c5c0721a1d0@news.povray.org>
I just rendered two partials without anti-alias, and the result is the same.
I think my best options are to render with sufficient overlap, say a 100 pixels
or so. Remember I have to do partials to avoid out-of-memory errors, but
enlarging them by 100 pixels won't make them too large. I hope.


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From: Christian Froeschlin
Subject: Re: color differences when doing partial renderings
Date: 12 Jan 2011 17:56:52
Message: <4d2e31b4@news.povray.org>
stevenvh wrote:

> Yes, I am, but as I understand it radiosity influences pixels color through the
> object's color in the scene, not the (adjacent) pixels in the image.

I think due to the algorithm for collecting samples there might
be artefacts that depend on the rendered part. You could try using
the command line options +RFI and +RFO to reuse already collected
radiosity samples for the next part, maybe this helps the borders.


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From: clipka
Subject: Re: color differences when doing partial renderings
Date: 13 Jan 2011 07:13:57
Message: <4d2eec85$1@news.povray.org>
Am 12.01.2011 14:31, schrieb stevenvh:
>
> Yes, I am, but as I understand it radiosity influences pixels color through the
> object's color in the scene, not the (adjacent) pixels in the image.

That's right, but as radiosity is a sample-based algorithm, results 
depend on where exactly throughout the scene the radiosity samples are 
taken. This in turn depends on the exact order in which the pixels were 
rendered during pretrace - which in turn depends (a) on which areas are 
covered by pretrace anyway (which obviously differs between renders of 
different subsection of the image) and (b) on thread scheduling by the 
OS (which may be different even between two renders with exactly 
identical parameters).


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