vray 3.0 motion blur

[o-v]

Hello

I have a little an issue with motion blur quality in vray 3.0 using the physical camera.

1) i can't find the "subdivisions" setting. the are not (as suggested by the help file) in the vray camera rendering settigns, nor in the camera settings itself.

2) the quality is controlled by the image sampler - which is stated in the help file and seems to be so, but I have to setup an insane min shading rate (like 3645) and still having some grain in the motion blur.

the case is I'm rendering light trails... fast moving star-like object

rendering isn't that slow at all per frame (2.43 min) but as I have to add more complex and textured geometry into the scene, it may skyrocket that. I guess.

so how can I improve the quality without killing the rendertimes?

EDIT: @shader:

its a vray light shader with a ramp texture in color. no lights at all in the scene yet, but will be required later on. the intensity is at 10 yet. rising the intensity to 60 kicks the rendertime to 7:51 min. not good. the effect is much better though.

an example:





thank you very much in advance.

[joconnell]

It's not the shading rate that'll sort out the smoothness of the motrion blur, it's more your max AA settings. If you pop in to the adaptive subdivision settings which are min -1, max 2, it's the max AA setting which you want to look at.

[o-v]

thx a lot

got it.

[o-v]

Now I have a different issue: alpha chanel is pitch black...

where the glitch in my logic?

thx for any hint.

[joconnell]

See if you can use the colour picker on pixels that are filled in the rgb - it might just be very weak.

[o-v]

yes they are very weak, which is completely useless.

[joconnell]

Right - what do you intend to do with this in the end? For something like a light trail, you can just additively blend this over any bit of footage and it'll be nice and bright. The alpha will likely always be weak since you've a very small object that only takes up a small amount of screen space for a short amount of time. For example if you didn't have a bright light on the object you probably wouldn't see a lot in the rgb either.

[o-v]

yes - exactly thats my intention. but the object has a vray light shader assigned. therefore its pretty bright in the buffer (intensities from 1 to 90 tested). It seems that the alpha ignores the RBG values, which is logical but confusing a little... so I'd have to compute the alpha based on RBG in post, which needs a little creative work an combine it with alpha of the other geometry in the scene...

[Neilg]

render in passes, ignore alphas & use additive blending modes.

[joconnell]

yes - exactly thats my intention. but the object has a vray light shader assigned. therefore its pretty bright in the buffer (intensities from 1 to 90 tested). It seems that the alpha ignores the RBG values, which is logical but confusing a little... so I'd have to compute the alpha based on RBG in post, which needs a little creative work an combine it with alpha of the other geometry in the scene...

Yeah indeed. What's happening is that you've got a white alpha for a solid object, but if your white alpha is only appearing in part of the frame for maybe a tenth of the motion blur duration for the entire frame, it doesn't have enough time to "build up" into solid white, and you end up with a tenth of the alpha value instead. For your colour part, if you had a normal white material (no vray light shaders) of colour (1.0, 1.0, 1.0) then again you'd have white moving through your frame but only being in each part of the frame for a tenth of the total duration of the render so your white would be dulled to a dark grey. With light materials, if they're way brighter than normal white, they'd burn out if they sat in the same place but again if they get spread over the entire frame and motion blur, they get dulled down a bit. The difference between your RGB and your alpha is that the alpha can only ever be a max value of pure white. Your RGB can be way way brighter than that so even if the motion blur is spreading out that colour over the distance the object moves over, it can still be so bright that it shows up.

[DanielWichterich]

coming back to the original question. is there really no option other than raising the max aa setting? in an animation you are wasting a lot of render time on frames which happen to have not so much motion, right?

[o-v]

well actually you don't have to rise the max min settings that much, but the DOF/mblur subdivs... and yes. you max expect skyrocketing the rendertimes.

but you will have still the huge problem of alpha. the prob is - it needs a background. even calculating the alpha out of RGB values will have huge issues. as soon as the blur occures over some other geo, it will look different than over "nothing".

[DanielWichterich]

what mblur subdivs do you mean?

[o-v]

those:

[DanielWichterich]

ok, thanks. sorry for stupid questions, i am not at my pc. i wonder, is there something equal for dmc?