Weird rendering artifacts not appearing when rendering a small area with border

Hi! I’m becoming mad with a weird rendering problem.

I am currently working on a setup allowing realistic fake volumetric clouds, and I’m very close to the goal, but there are still weird artifacts in my cloud, visible on some frames in my animations.

The topic about my WIP is here :

I plan to release the Blend file with a tutorial, but as I want to deliver something really usable, I have to fix this little but annoying problem :

Some weird artifacts appear on some frames in areas mostly in peripheral, around my cloud. I have checked dozens of parameters, but as the phenomenon doesn’t appear when rendering only a part of the image around the artifact using border rendering, it looks very strange !

I fear that it is a bug in the render engine… In such case, all my attempts to fix this problem by tweaking parameters in the materials, lights and else would be only a waste of time…

If someone has an idea about why it doesn’t happen with border rendering, I’d be the most happy of the Blenderers…

Raytracing is disabled as well as material specularity, so no possible reflections between objects. I don’t think that parts rendered with border can be influenced by something in an other part of the image.

If I dont find, I will release the Blend file as it is, in the hope that someone will find a solution, but it is rather annoying so close to the goal !

Any suggestions are welcome.

Thanks in advance.


when I tried this I got much more crazy effect.
I couldnt wait 24 hours :slight_smile: so i think that in my electric flash in clouds (time before cloud gen.) is because planes are to far each other and that the same with your artefacts in animation. I mean that planes change to much distance from frame to frame for sss calculation and this make this strange behaviore. anyway good job :slight_smile:

Thank for your response, but it doesn’t explain why the phenomenon doesn’t appear when rendering a small part of the image with border rendering. This makes me think that it is not a setup problem but a rendering problem…

Did you try to render the frame of my blend file 45 only, with a small rendering area selected ?

I’have tried your blend file. The array system is a good idea, but there is a weird pump effect in average each 21 frames. It affects the motion of the parallel planes…

This can be avoided by using a rotating empty placed at the center of the scene, instead of a curve path. I tried with the camera parented to the rotating empty, and there is no more pump effect in the array duplicated planes.

Also, full surfaces instead of billboards increases the computing time.

Hi, I forgot to tell you something : if you move your half transparent planes in the 3D world, as the texture is in 3D, the texture on each plane will change at a various speed when the planes are rotated = Constant rotation speed means variable linear speed for each point located somewhere one a plane. When you translate all planes, all the clouds inthe 3D space will be affected by the same flicker effect, because they have the same linear speed. When you roptate the planes instead, you get interferences,because accroding to the level of details of your textures and the speed of each moving pint , there will be mixed frequencies everywhere in your images, with high energy points and low energy points. This is the cause of your weird “electric lightning” effect !

This happens with large planes, but is less visible with small billboards (small rotating surface=smaller linear speed), but can occur as well if they rotate very fast.
This said, as the problem doesn’t show with Border rendering ,I’m not sure that it is the case in my animation…

I haven’t edited the previous post to bump the topic and make sure you will have this explanation.

Hi, ok, its hard to say what is the reason of your artifacts. The sharp edge ofplanes i rendered only on full screen. Its not rendered on border one. Did you try other renders (Yafray, Indigo etc.)?

ad2( other not unreallistic think that looks strange for me is a behavior of light when camera flies around.

anyway have you seen this?

And thanks for your testing of my old test but its totaly wrong way it relatively works for only some kind of movement, and totaly without control of cloud shapes. I just wanted use cloudy sky without thousand of planes. And about pump array effect is it strange with older version of blender it worked correctly.

p.s.: also doesnt work correctly for me on 2.48a (os X, intel). Its a pity.

Good luck


I’m Clumsy with Yafray, and I like indigo, but it would take months to render volumetric and animated clouds with it, I think !

Sorry for the On Windows it works corectly, but the console returns some warnings about deprecated syntax. David wrote it a long time ago. I will ask him if he could give an eye to the script and solve the problem.

Yes, I have seen the video about volumetric clouds, but I think that it has been done with fake volumetrics, using planes like we did… with a better lighting. The shadows seems to have been faked with a dark texture… but I’m not sure !

In my own video test, the strange behaviour of the light when the camera is moving is due to the fact that you need to have always a light source behind the clouds to keep them looking bright. In my example, the camera is moving, but the lamps are not. At the end of the video sequence, the light beams are almost parallel to the billboards, and the cloud becomes almost black because it can’t stop the light, which is passing through it without casting on it !

I did a first trial wit a background light parented to the camera and the visual effect was more constant, but the shadows were less visible… it is difficult to keep the effect eficient wit a camera moving all around the cloud. In most scenes, the camery flies with few rotations, and it works fine.

just about the volumetric video - on the bottom of article there is blender and .blend file too to see how it works.

Wow ! Thank you, vklidu !

I hadn’t seen the links. I have downloaded the Special Blender build and the Blend file. I have just opened it, but it looks very interesting. I will do some experiments as soon as possible on my best computer, because the one I use for Internet is the oldest one.