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I'm having problems with a scene I'm trying to render for animation. I'm using HDRI and two emissive planes for lighting. When the figure walks towards the emissive plane it seems to cause a grainy effect in the lighting of the figures head and neck the closer it gets to the plane. The lighting on the rest of the body is fine with no graininess.

Is this graininess caused because the figure's head is too close to the emissive surface? Or is it caused because the emissive power is set too high? The lighting of the rest of the figure is fine - it's just the head and neck that cause this grainy effect when the figure walks close to the emissive plane.

At first I thought this might be a resolution problem so I increased max samples but this didn't help. I think this might be caused when the figures head gets too close to the emissive surface. I'm trying to find a way to achieve the same lighting set up but without the graininess.

is the emissive plane in the frame of the camera? I tend to avoid that myself.

but yeah, sounds like it may be too close. but i can't tell. I tend to keep lights at ceiling height and if they are any closer I still keep them out of the frame.

Thanks for your reply. The emissive plane is in the frame but the opacity is set to zero so they aren't visible. Does having them in the frame, even when opacity is set to zero, cause graininess? I'm also wondering if this is a resolution problem. I've got max samples set to 1000. Is this normally enough resolution to render emissive lights fully? I've applied IES spotlight files to the emissive lights. Do IES lights require greater resolution to render fully?

Spectralis wrote:I'm having problems with a scene I'm trying to render for animation. I'm using HDRI and two emissive planes for lighting. When the figure walks towards the emissive plane it seems to cause a grainy effect in the lighting of the figures head and neck the closer it gets to the plane. The lighting on the rest of the body is fine with no graininess.

Is this graininess caused because the figure's head is too close to the emissive surface? Or is it caused because the emissive power is set too high? The lighting of the rest of the figure is fine - it's just the head and neck that cause this grainy effect when the figure walks close to the emissive plane.

At first I thought this might be a resolution problem so I increased max samples but this didn't help. I think this might be caused when the figures head gets too close to the emissive surface. I'm trying to find a way to achieve the same lighting set up but without the graininess.

I think I may have seen this, myself, but I can't be sure.
I tried changing a few things, which ended up fixing it or at least making the undesired effect less noticeable.
One thing I tried was lowering the power of the emission (and then raising the exposure value slightly in the renderer to compensate).
The other thing I tried, I saw mention of in here, and didn't think it would work -- I decreased the "hotpixel removal" value from 1 to about 0.5 or less. You would think it should have the reverse effect, but it actually helped quite a bit in removing the graininess.

I can imagine the effect you describe is something about the light bouncing back and forth between the subject/object and the emitter, and getting amplified each time it travels, but I'm no Physics expert.

leblancd wrote:

Spectralis wrote:I'm having problems with a scene I'm trying to render for animation. I'm using HDRI and two emissive planes for lighting. When the figure walks towards the emissive plane it seems to cause a grainy effect in the lighting of the figures head and neck the closer it gets to the plane. The lighting on the rest of the body is fine with no graininess.

Is this graininess caused because the figure's head is too close to the emissive surface? Or is it caused because the emissive power is set too high? The lighting of the rest of the figure is fine - it's just the head and neck that cause this grainy effect when the figure walks close to the emissive plane.

At first I thought this might be a resolution problem so I increased max samples but this didn't help. I think this might be caused when the figures head gets too close to the emissive surface. I'm trying to find a way to achieve the same lighting set up but without the graininess.

I think I may have seen this, myself, but I can't be sure.
I tried changing a few things, which ended up fixing it or at least making the undesired effect less noticeable.
One thing I tried was lowering the power of the emission (and then raising the exposure value slightly in the renderer to compensate).
The other thing I tried, I saw mention of in here, and didn't think it would work -- I decreased the "hotpixel removal" value from 1 to about 0.5 or less. You would think it should have the reverse effect, but it actually helped quite a bit in removing the graininess.

I can imagine the effect you describe is something about the light bouncing back and forth between the subject/object and the emitter, and getting amplified each time it travels, but I'm no Physics expert.

Thanks! I'll try the hotpixel removal because I'd rather not increase the exposure of the whole scene. I'm not sure what's causing it because I also noticed some graininess on one of the feet when the figure is stationary for awhile and that foot is quite a distance away from the emitter.

hi,
please, could you share a rendered image and a couple of orthographic screenshots in order to better understand the emitters dimensions and position?
I would like to reproduce the scene for helping you but I need more infos
ciao beppe

bepeg4d wrote:hi,
please, could you share a rendered image and a couple of orthographic screenshots in order to better understand the emitters dimensions and position?
I would like to reproduce the scene for helping you but I need more infos
ciao beppe

Thanks for trying to help Beppe. Here's a link to a section of the animation.

http://www.videosprout.com/video?id=f76 ... 2a40557ae5

If you look closely at the neck area and top of the head of the figure there's a graininess in the light areas. Also some graininess on the figure's left foot at certain points in the animation. One of the emitters is situated top left just above the face and the other is slightly behind the figure to the right. The upload is more compressed than the original. In the original the graininess is much more obvious.

are you rendering with coherent ratio on by any chance?

Kinda sorta, but not exactly reminds me of what I saw when i rendered a turntable animation with coherent ratio on.

larsmidnatt wrote:are you rendering with coherent ratio on by any chance?

Kinda sorta, but not exactly reminds me of what I saw when i rendered a turntable animation with coherent ratio on.

Where can I find coherent ratio and how do I switch it off?

Spectralis wrote:

larsmidnatt wrote:are you rendering with coherent ratio on by any chance?

Kinda sorta, but not exactly reminds me of what I saw when i rendered a turntable animation with coherent ratio on.

Where can I find coherent ratio and how do I switch it off?

I think by default it is off, so may not be your issue. Unless you use final render mode. Also it is not available for PMC mode but not sure you mentioned that or not.

This setting can greatly speed up renders, but works best for stills or low speed, well lit animations. It may not be at all the case for you. but may be useful one day. The issues you are seeing are not exactly what I saw when I used this setting anyway, but was worth a shot.

I attached where the setting is for the final render menu and rendering settings just in case.

0 is off. 1 is full blast. Terrible to use during previews! Not a bad option for final renders(great speed increase, but has quirks and strange artifacts for animations at times).