LuxCoreRender Forums

albedo.png position.png

As the picture showing, there are some larger white spots and lots of gray spots in POSITION Channel picture. And there are some black or gray spots in ALBEDO Channel.
What is the reason of this phenomenon。

The pictures are renderred by LuxCoreUI.

Here is an answer from this thread:

viewtopic.php?f=5&t=2084

Dade wrote: ↑Wed Apr 22, 2020 3:10 pm Because LuxCore is a "pure" path tracer without path-split: for instance, if you have glass, the path will be reflected or refracted (i.e. not both paths will be followed) and, with 1 samples per pixel, you will have something looking half way between a mirror (reflected paths) or a transparent object (transmitted paths).
However there should be no noise on a matte object (i.e. I need to see your scene to be able to tell more).

Thx.
But I think that Geometric channels outputs are obtain and saved in sampleResult when camera rays are intersected with object at the first bounce. In my perception these channels' outputs are independent of material.

MonkeyDLuffy wrote: ↑Mon Apr 27, 2020 11:35 am But I think that Geometric channels outputs are obtain and saved in sampleResult when camera rays are intersected with object at the first bounce. In my perception these channels' outputs are independent of material.

Yes but there is another factor: halt conditions are asynchronous so they will never render exactly 1spp. However they should always render more, not less.

Are looking at the AOV saved on files after the end of the rendering ? Or getting their content from the LuxCore API ? Version used ?

Oh, I got that these big white and bright spots were probably caused by LuxCore multithreading asynchronous rendering or I save these pictures at the wrong time point, what did you mean.
Use LuxCoreUI V2.3.
What's more, I also use BlenderLuxCore with 2spp rendering the same scene, and found that those light-colored spots are relevant to some specific material, such as this picture showing(Position channel). "disconnect the material node of the disc"
"result with the material node--Position channel"
"result without the material node--Position channel"

If you can isolate/simplify the problem (i.e. post a scene with just a plane showing the problem) I can check what is going on (as soon as I have time). Even only .cfg/.scn/.ply/etc. are fine, I always work from command line anyway.

Sorry, I reply to late because of time difference. I follow your advice and try to isolate/simplify the problem, finally, I find that the glossy translucent material node would impact results. "cube with glossy translucent material node"
Add a cube object and use glossy translucent material node, set "Opacity" to 0.500, then rendering with 2 SPP. I got the the following pitcures. "Shading Normal Channel output" "Position Channel output"
I would appreciate it if you know the reason for this phenomenon.

MonkeyDLuffy wrote: ↑Tue Apr 28, 2020 8:02 am Add a cube object and use glossy translucent material node, set "Opacity" to 0.500, then rendering with 2 SPP. I got the the following pitcures.

But if you set opacity to 0.5, it will hit a face of the cube only 50% of the times so this result is normal (or am I missing something ?). This is due to the reason Zeealpal linked as first answer. It is not like the ray color is multiplied by 0.5 and the path always continued, Opacity is really the probability to hit the surface.

First of all, thank you very much for your patience in answering my questions. Sorry for misunderstanding the reason Zeealpal linked.
But, I still have a few doubts(I'm a rookie in this field ):
1. I still think that the geometric channels' outputs are unrelated to the material properties(If there is a problem with my understanding, please let me know). Or LuxCore's method is on the contrary with my view, if this is the case, please tell me the relevant code(I am learning LuxCore's code).
2. I am curious about that the edge of the object is not smooth, as the picture showing. "the edge of the object"
3. I'd like to reconfirm that the reason for this situation, whit and bright spots. After the rendering was over, after a while, I saved the pictures. There still are annoying white spots. Every pixel should has been rendered. "whit and bright spots"