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I'm rendering an animation (as an .exr image sequence) and some images have these tiles appear on the final render. It somehow only happens on surfaces that are closer to the camera. It looks like Blender is somehow calculating adjacent tiles differently in certain areas.

You can see them on this image as the faint, slightly darker squares. The distribution of these boxes in random every render-iteration.

Has anyone had the same problem? I've tried turning denoising off, changing the tile sizes, changing the sampling or changing the light paths etc., nothing helped.

enter image description here

chribit
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    Are you rendering on CPU or GPU? Try switching to just CPU to see if that helps. – Rich Sedman Jul 19 '19 at 19:45
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    @RichSedman both. good thought... that may actually be the cause... different hardware, different output. although that does not explain, why those boxes only appear in this particular scene, where the camera gets closer to the terrain than in the others...

    (i'll try once my current render finishes)

     – chribit Jul 19 '19 at 22:29
  • I know this is going to be very general but could you explain more about your setup, if you are doing anything in the compositor, or if you are running any scripts or doing anything special – Ben Jul 19 '19 at 23:42
  • This might probably help https://blender.stackexchange.com/a/12101/54300 – AshKB Jul 20 '19 at 00:24
  • Hmm, this is quite weird. Have you tried any other file type? Does PNG and or JPEG work? – Askejm Jul 19 '19 at 19:44
  • jep, that actually was my first thought too. But nope, same problem with any other single-image filetype (didn't try the movie filetypes... shouldn't make a difference though). – chribit Jul 19 '19 at 22:31
  • @Ben Sure, sorry I forgot that in the main post. No, i'm not using the compositor or anything special for that matter (no scripts etc.). The image above is just a rendered image directly from a regular cycles render. The scene itself just consists of a few static, hard-surface meshes (the aircraft etc.) and a plane with adaptive subdivision (using a 16bit displacement map created in world-creator-2).

    The tiles in the image are directly correlated with the tile-size i choose in the render settings (i.e. changing any maps or textures doesn't help).

    Anything else about the scene? :)

     – chribit Jul 20 '19 at 08:18
  • @AshKB not sure how that was supposed to help ^^ I'm not using any transparency shaders. – chribit Jul 20 '19 at 08:25
  • @RichSedman THAT DID HELP. The tiles disappear if my cpu renders everything alone... so my gpu somehow renders its tiles differently compared to my cpu... but how do i fix that?! I need the render-speed... this is an animation after all. – chribit Jul 20 '19 at 08:27
  • Glad that fixed it. I haven’t actually had much experience of GPU rendering so I don’t know how you could fix it other than disabling the CPU element (which you have done). I guess since the two methods use different processes to produce the result there mist be some subtle difference in the implementations somewhere. – Rich Sedman Jul 20 '19 at 08:46
  • Could you post a .blend? – Ben Jul 20 '19 at 16:52
  • I can easily reproduce this bug when replacing the default lamp in the default cube scene in Blender by an area light and scale it down. The smaller the light the bigger the issue. So for an light of about 1x1cm you can only throw the result away. When its bigger (e.g. 90x90cm) then you maybe only notice it in darker regions/shadows. I hope this bug will be solved soon. I have a scene of a short film project with small floor lights that produce this artifacts when combining CPU with GPU and I really like to use the power of both. – AtoMedia Design Sep 04 '19 at 17:51
  • I am having this exact same problem with 2.92 (and I think 2.83 LTS). I tried everything and my next step is to try CPU only. But this suggests that the bug is not yet fixed. I had the same problem with OPTIX and CUDA. – DrIgnatiusCole Feb 23 '21 at 13:22

5 Answers5

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Figured out the cause thanks to @Rich Sedman, so I guess this is a temporary "solution", as it doesn't really solve the problem, just finds a way around it.

The tiles appear in the render due to CPU and GPU handling the output differently for some reason. Deactivating the CPU in the CUDA settings not only solved the issue but also gave me 30 seconds faster render times per frame.

Not sure if that's an issue of the current 2.8 release candidate or just something that comes with combining two pieces of hardware for the same process. (Maybe my Geforce GTX 1080 ti doesn't work well with my AMD Ryzen 7 2700X?)

Robin Betts
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chribit
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The opposite can happen too. My animation had bad tiles on three frames. I ran the frames over again with the exact same errors. Following the advice in this string, I turned ON CPU and GPU and bingo, problem solved.

Glenn Smith
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Something quite similar has happen to me when rendering a complex scene on both CPU and GPU, but running only on GPU didn't solve the case. It wasn't darker squares that were appearing, but we could see transitions between tiles, a thing that generally is due to too tiny render tiles, but this time I tried with huge tiles, and the problem persisted. The only way I found to clean this was to set tile size to fill the entire screen.

BarryCap
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True! Problem solved disabling CPU from CUDA selection (Intel Core i5 9400F - Nvidia Asus ROG Strix 1060 6GB) and seems faster too! Not sure why, but not complaining lol

Arisyn ILY
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This constantly happens to me. I can't render on GPU only, since my GPU memory is too low. So it's either CPU only or completely unpredictable results. In some images, it works fine in "mixed" mode. Others look like Tetris gone wrong. Someone blamed the denoiser, but I also turned denoising off, same result.

A few samples are attached! Reflections on metal & glass

dark surfaces right, sofa left

without denoiser

with denoiser

Markus Schlögl
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