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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

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    $\begingroup$ Could be z-fighting, make sure you don't have any coplanar overlapping geometry on the ground. Could you upload the .blend? $\endgroup$ – PGmath Mar 6 '16 at 15:56
  • $\begingroup$ There are no coplanar polys anywhere in the scene. Blend uploaded.<img src="http://blend-exchange.giantcowfilms.com/embedImage.png?bid=1086" /> $\endgroup$ – DrStrik9 Mar 6 '16 at 17:37
  • $\begingroup$ 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? $\endgroup$ – DrStrik9 Mar 13 '16 at 13:41
  • $\begingroup$ Here is a visual comparison between GOOD frames and BAD frames: s-media-cache-ak0.pinimg.com/originals/62/fd/60/… These are rendered as 16-bit TIFF, if that makes a difference ... $\endgroup$ – DrStrik9 Mar 13 '16 at 14:10
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    $\begingroup$ could you upload the scene? $\endgroup$ – diramazioni Mar 13 '16 at 14:57
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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)

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  • $\begingroup$ 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. $\endgroup$ – DrStrik9 Mar 21 '16 at 0:36
  • $\begingroup$ Please see the new scene 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. $\endgroup$ – DrStrik9 Mar 21 '16 at 1:28
  • $\begingroup$ Here is a side-by-side frame comparison between good and bad: s-media-cache-ak0.pinimg.com/originals/76/43/f6/… $\endgroup$ – DrStrik9 Mar 21 '16 at 1:44
  • $\begingroup$ BTW, this is CPU rendering (not GPU). I'm continuing to render this 880-frame animation, and it continues to flicker ... $\endgroup$ – DrStrik9 Mar 21 '16 at 3:37
  • $\begingroup$ On what scale did you modeled the scene? $\endgroup$ – Delagone Mar 21 '16 at 9:26

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