On 6/17/2019 11:08 AM, BayashiPascal wrote:
> Hi there,
> I've realized something I wasn't aware until now and wanted to ask for your
> opinion. I'm using partial rendering (don't know if it's the right term, I mean
> rendering the image by chunks instead of in one pass) on a current project and
> I've made a unit test to check if my automatic procedure reuniting all the
> chunks give me the right result, i.e. give me the exact same image as the one
> rendered in one pass. As you can guess, I don't get the same image and the
> problem is not in my procedure.
> So, I've made a simple test case to investigate further. What I've found is that
> with antialiasing turned on, the image by chunk is different from the image in
> one pass. Then I thought there should be some randomness in the subsampling used
> for antialising, maybe the seed is different at each rendering. So I've compared
> two renderings in one shot, and there was no difference, which leave me with no
> clue.
> That's not a very big problem to me, but I'm wondering if it's known, if it's a
> bug, if I'm doing something wrong, ...
> If you wish to check yourself: I'm using POV-Ray 3.6.1 on Ubuntu 16.04, the
> simple test case I've used is
> 
> --- testPov.pov
> 
> camera {
>    location 5
>    look_at 0
> }
> 
> light_source { 10 color rgb 1 }
> 
> background { color rgb z }
> 
> sphere { 0 1 texture { pigment { color x } } }
> 
> --- end of testPov.pov
> 
> --- testPov.ini
> 
> Input_File_Name=testPov.pov
> Width=100
> Height=100
> Antialias=on
> 
> --- end of testPov.ini
> 
> --- Makefile
> 
> oneShot:
>   povray testPov.ini -D +OoneShot.png
> 
> fourFragments: firstFragment secondFragment thirdFragment fourthFragment
> 
> firstFragment:
>   povray testPov.ini +SC1 +SR1 +EC50 +ER50 -D -OfirstFragment.png
> 
> secondFragment:
>   povray testPov.ini +SC51 +SR1 +EC100 +ER50 -D -OsecondFragment.png
> 
> thirdFragment:
>   povray testPov.ini +SC1 +SR51 +EC50 +ER100 -D -OthirdFragment.png
> 
> fourthFragment:
>   povray testPov.ini +SC51 +SR51 +EC100 +ER100 -D -OfourthFragment.png
> 
> --- end of Makefile
> 
> Result of rendering in attachment. First line, two rendering in one pass and
> their difference. Second line, rendering in one pass, rendering by chunks, their
> difference (no antialising). Third line, rendering in one pass, rendering by
> chunks, their difference (with antialising, check the value of the pixels at the
> limit of the sphere and the background, they are not [0,0,0]). Both Gimp and my
> code give me the same differences so I'm confident the culprit is POV-Ray.
> 
> Regards,
> Pascal
> 
> 
> 

You might try disabling "jitter" in the INI file.


Michael

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