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Unexpected white spot with certain Caus. Photons values

Wed, 24/02/2010 - 20:45 — Lensshift
Project:YafaRay
Version:0.1.x
Component:Code
Category:bug report
Priority:normal
Assigned:Unassigned
Status:closed
Description

Hi there,

though I can't rule out an user error I've denoted the following observation a bug report.

Here we go:

With a certain value for the Caus. Photons setting (here: 5000 vs. 50000 or 500000) I see an unexpected white spot coming up (see image attached).

The .blend file attached has two relevant render settings:

OK - NoSpot (Caus. Photons: 50000)

Weird - Spot (Caus. Photons: 5000) -> see image provided.

 

My environment:

Windows 7 x64, i7 920, 12megs ram

Blender 2.49b

YafaRay-0.1.x.DT-538-win32

 

Cheers,

Lensshift

 

AttachmentSize
WhiteSpot_ByLow Caus.Photons.jpg340.46 KB

Comments

Wed, 24/02/2010 - 20:51 — Lensshift

#1

Oups,


obviously I can only attach one file per "post" (though uploading a 2nd one wasn't disabled).


So, hopefully here's the .blend file.


 


Cheers,


Lensshift

AttachmentSize
WhiteSpot_ByLow Caus.Photons.zip 429.75 KB
Fri, 26/02/2010 - 11:16 — Yaroslav_L

#2

Assigned to:Anonymous» Yaroslav_L

The same problem.

Linux Ubuntu (Mint 8 x64)

YaR 538

Blender 2.49b

Photon Map

No caus photons

64 samples on Portals, Sun and SkyLight

Depth 16, 2.500.000 photons, DiffRad 0.5, Search 180, FG Samples 256, FG bounces 6, RayDepth 6, ShadDepth 4, 9!!! hours of rend on Core2Quad!

AttachmentSize
Yaroslav_Lebodko-Ochotnica-06a.jpg 639.83 KB
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_______________
Yaroslav Lebidko.
Interior design. Architecture visualization.
http://www.3DXATA.com

Sat, 27/02/2010 - 19:10 — Aspen

#3

Assigned to:Yaroslav_L» Anonymous

 

Hi,

I took a look at your files guys and found out that it actually isn't a bug (as far as i tested it) so you surely wonder, where do the spots come from ?

Here is what i know that happens:

First of all you all have caustic photons shot from light sources (tested on this scene → http://www.yafaray.org/sites/default/files/issues/WhiteSpot_ByLow%20Caus...)

and the console output says:

INFO: PhotonMap: Shot 5000 caustic photons from 5 light(s).

INFO: PhotonMap: Stored caustic photons: 13

INFO: PhotonMap: Stored diffuse photons: 2453895

However in settings the caustic photons have radius as big as 1 (BU or meter in yafaray) that means that your caustic photons are 1 meter in diameter (which is pretty much correct if you look at this picture http://www.yafaray.org/sites/default/files/issues/WhiteSpot_ByLow%20Caus...) and you have 13 caustic photons that actually hit a surface so there is probability to see at least one of the 13 caustic photons. Now, when you change the number of photons, they aren't only added to the scene, but they hit surface differently in some other places, so if you have lets say 500 caustic photons and you can see one of them, i'd guess you'll not see any at 501 or 499. Generally, if you'd look around your model, you'll surely find 12 other spots somewhere else because they hit the surface. The solution to this is to use 1 caustic photon (and make sure it doesn't find any target) so you skip the spots, you already have no advantage of the caustics so it's simply better to switch them off. The more caustics the higher probability to see them but you may be lucky and see them even with low value, and that's pretty much what you got ;)
Greetings
Aspen
Sat, 27/02/2010 - 19:33 — Lensshift

#4

Hi Aspen,

thanks for your elaboration. I think I got what you wanted to point out - quite likely it's an user error. ;-)))

In my understanding finally that means using these caustic options is heavily prone to a trial & error approach.

 

Cheers,

Lensshift

Sat, 27/02/2010 - 20:15 — Aspen

#5

Hi Lensshift

Yes, it's pretty much that way, i also made some comparison between the results with one caustic photon and 5000 of them.

 

http://www.yafaray.org/sites/default/files/issues/no_photons_few.png

Here we have the scene rendered with 5000 caustic photons and 13 hits (actually if you look closer you can see 4 visible photons on the scene the first one is there in the left corner in the middle of the image, edge between wall and floor, the second is of course the one you pointed out and the 3rd is in front of the doors to the right, the fourth i noticed latest is on the ceiling left upper corner)

 

http://www.yafaray.org/sites/default/files/issues/no_photons.png

here is the clean render with one photon shot and 0 hits (clean render)

AttachmentSize
no_photons_few.png 755.72 KB
no_photons.png 782 KB
Tue, 30/08/2011 - 10:11 — Samo

#6

Status:active» closed
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http://samo.cgsociety.org/gallery/