Strange motion blur with rotor blades ?

[anthonyh]

Hi,
I`ve got motion blurred helicopter blades, but when the main rotor renders in front of the rear rotor you get a strange stripe. Is this right ? It might be correct I don`t know but it just looks weird.
2016 with Vray 3.4.0.03 but I`ve also tried 3.6 latest nightly as well.
cheers
anthonyh

[Morbid Angel]

hmm interesting, a few questions - is this shape in alpha? or perhaps its specular / reflection? Can you check the aovs and see if it shows up in any of them. Also if main rotor is rendered on its own does it have that issue, same for small one?

[anthonyh]

Hi,
thanks for replying.
I checked and it does affect the alpha(see below), it`s more transparent along that strange curve.
I checked each rotor individually and they work fine, no anomalies. This only happens when rendered together so that would rule out reflections/specular I`d think ?
I tried a different view and the same thing happens. I`ve also tried without lights/shadows/reflections/glossy effects, override material, bucket/progressive. Turning everything I can think of off/on, reset Vray too.
Here`s the view of the alpha with faster rotation that shows the anomaly a bit better.

Luckily the client hasn`t noticed so it`s not a big issue but it still looks weird. I don`t know if this is rendering technically correct but just looks odd or a bug or something in my scene setup is janky.
anthonyh

[Morbid Angel]

So this is interesting, I got the same effect as you did in few minutes of testing. I'm not sure, perhaps the devs can check out this scene it appears to be shading anisotropy but I don't think its correct.

For the devs, I've also experienced a bug with noise dots in motion blur when shutter efficiency was lower then 1, see attached scene and image. This is with vray next.

[Morbid Angel]

So then I tried this setup in redshift and arnold, both produce those kind of artifacts so I suppose its correct

[anthonyh]

Weird, although I like that it looks like a smiley face ! This effect probably has a reason I guess ? Odd because it just doesn`t *seem* like that would happen, I`m going to try and find some real footage and see what that looks like. As for the dots I often get missing chunks on the edges of motion blurred areas not sure it`s the same thing though,
I tried to have a go with Arnold a couple of days ago but it just instantly crashes when clicking to add materials, not sure why. it renders ok but I can`t apply materials to anything. Maybe my machine is too old for it, I know it recommends drivers Geforce 39.xx and up for Gpu rendering and mine are Quadro 36.xx since my gfx card is so old.

[Morbid Angel]

the missing stuff on the edges is min samples in dmc, just set that to 2 or 3.