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Cycles Render. I have a simple scene, with a plane as ground, and objects on it. It is lit by a HDR background texture and one sun lamp, and being rendered to 16-bit TIFF individual frames. The ground plane color begins to flicker a darker version of the same hue after about 240 frames, and then eventually goes to the darker color after a dozen or so flickers over the next 120 frames. The ground material is simple Diffuse BSDF ... What is causing this flicker?

See flickering animation at: https://youtu.be/QSf4CFDx6Zk

DrStrik9
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    Could be z-fighting, make sure you don't have any coplanar overlapping geometry on the ground. Could you upload the .blend? – PGmath Mar 06 '16 at 15:56
  • There are no coplanar polys anywhere in the scene. Blend uploaded. – DrStrik9 Mar 06 '16 at 17:37
  • This morning I am seeing this same bad rendering behavior on a different scene. At Fm 262 onward, the ground plane is rendering darker, with a dividing line between darker values at a 45-degree angle, with half of the plane color rendering even darker. This is RUINING the render. I tried rendering the offending frames again, but always get the same horrible result on those particular frames. :-( Why, why, WHY? – DrStrik9 Mar 13 '16 at 13:41
  • Here is a visual comparison between GOOD frames and BAD frames: https://s-media-cache-ak0.pinimg.com/originals/62/fd/60/62fd607846e707a81f07a140311abd8c.jpg These are rendered as 16-bit TIFF, if that makes a difference ... – DrStrik9 Mar 13 '16 at 14:10
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    could you upload the scene? – diramazioni Mar 13 '16 at 14:57
  • @ diramazoni -- It's 201.1 MB (baked rigid-body) ... I uploaded a simpler scene that had the same problem before, same ground plane asset, no changes ... (see above) ... but I'll try ... NOPE, upload size limit is 30 MB. – DrStrik9 Mar 13 '16 at 15:45
  • @Mr Zak - I tried your suggestions: no change. I'm noticing that the lower-res (25 samples) preview renders do NOT have this problem, only the large full-res (150 samples) renders do. – DrStrik9 Mar 13 '16 at 22:47
  • Rendered 262 frame of your animation, I don't see anything bad (HDR is another one because yours wasn't packed in file). Still if it persists and is present only on final render then the culprit might be in differences between them. See technical differences for details. Try disabling Motion Blur, changing camera's settings to default ones, using Clipping values as low as possible, change HDR to another one (though I don't think it can be reason), in world material set HDR to Non-Color data. – Mr Zak Mar 14 '16 at 16:42
  • @ Mr Zak - In that earlier scene which I uploaded, the same errors happen at difference times. Please try seeing if you get a difference in ground-plane value between rendered frames 0276 and 0277. I will also try your suggestions on the newer/larger scene. On technical diffs, I get the same errors with F12 as with ctrl-f12. – DrStrik9 Mar 14 '16 at 17:15
  • So it appears that disabling Motion Blur doesn't really solve the problem ? (btw thank you for your letter, I'm glad to be of help). Unfortunately I can't proceed to testing as I couldn't reproduce the problem (frames mentioned rendered fine for me, but of course I didn't render whole animation). I'm really curious to learn what's wrong with this scene and whether this is a bug. Try importing exact these objects with exact this lighting into another scene and rendering it there. The only thing - what version of Blender do you use ? I don't think I know what's going on there as for now. – Mr Zak Mar 21 '16 at 23:08
  • @ Mr Zak: Sometimes turning MB on or off and re-rendering a bad frame can correct the darkened objects, but most of the time, this is of no help. It is a great disappointment, and a hugely time-wasting frustrating mystery. – DrStrik9 Mar 22 '16 at 15:57
  • did you find solution? I have the same problem on Blender 3.6 .... Wtf is this? – Никита Харлов Jul 20 '23 at 11:10

1 Answers1

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It is most likely Z-fighting. Break down the scene and look if there are any planes in the exact space of orientation. 1 - Could be a hidden object in viewport but still enabled in rendering enter image description here

2 - Maybe it is an object that is hiding in a different layer. 3 - It could also be 1 object with 2 overlapping faces in the exact same location. (go into edit mode and pull away some edges to check)

Delagone
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  • It's not z-fighting, as stated before. No hidden objects. Nothing in any layer except layer 1. Nothing duplicated in the same space. -- I hate to report this, but on yet another scene (for the third time, with all fresh objects) this is happening again, but the darker frames also include ALL objects, not just the ground plane. The only thing that is not darker on the offending frames is the HDR background. The single lamp (sun) in the scene is NOT keyframed, and does not move or change during the scene. I'll post this render on YouTube with a link when it's finished. Blender 2.77. – DrStrik9 Mar 21 '16 at 00:36
  • Please see the new scene https://youtu.be/dviikkFAsRQ at around 7:20. The render was aborted after several bad frames. The darker frames include ALL objects, not just the ground plane. But the ground plane has that telltale 45-degree angle darker triangle, as before. I'd love to share the scene but it is too large to upload. I am stumped, and VERY frustrated. – DrStrik9 Mar 21 '16 at 01:28
  • Here is a side-by-side frame comparison between good and bad: https://s-media-cache-ak0.pinimg.com/originals/76/43/f6/7643f653d7f87c4a0ba2c70859eed3fa.jpg – DrStrik9 Mar 21 '16 at 01:44
  • BTW, this is CPU rendering (not GPU). I'm continuing to render this 880-frame animation, and it continues to flicker ... – DrStrik9 Mar 21 '16 at 03:37
  • On what scale did you modeled the scene? – Delagone Mar 21 '16 at 09:26
  • Scale: The dimensions of each plank is exactly X = 6.5, Y = 0.5, Z = 1.0. – DrStrik9 Mar 21 '16 at 11:18
  • The only thing I can then come up with is that the uv's are possibly generated? Try ncluding a texture coordinate node in the material and set it to uv.(if it's unwrapped) – Delagone Mar 21 '16 at 15:14
  • There are no UV's. All surfaces are simple mix nodes with diffuse and gloss. Alternatively, could this be a bug with CPU render? It's on a 2013 MacPro with AMD video cards (no GPU). I've seen other threads about the differences between CPU and GPU renders. – DrStrik9 Mar 21 '16 at 17:03
  • Mr Zak solved this, but I got side-tracked and didn't try his suggestion a week ago to turn MOTION BLUR off. I don't know why, but turning motion blur off has solved this problem which has been plaguing me for several weeks. Thank you, Mr Zak! I'm sorry I didn't try your suggestion before. Now my question is: WHY? And of course, I need to be able to corner this bug in a super-simple scene and report it well ... – DrStrik9 Mar 21 '16 at 19:39
  • I guess I spoke too soon on the solution. MOST of the offending frames have been re-rendered OK with motion blur off, but there are still a few hold-outs which render DARK. I don't get it. This is a bizarre mystery, which makes no sense to me ... still searching for the solution. :-( – DrStrik9 Mar 21 '16 at 20:40